Tensile Strength of AR-10 and/or AR-15 Between Barrel Nut and Upper Receiver
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    Default Tensile Strength of AR-10 and/or AR-15 Between Barrel Nut and Upper Receiver

    I'm not a person inclined to "leave well enough alone". (However, I do believe strongly in "Don't fix what ain't broke".)
    I'm also not stupid or foolish. (I have made it to 64 with all my parts and faculties in spite of starting to reload when I was 16, and starting to making rifles when I was 50.) So...

    While building another AR-10-based wildcat (this one chambered in 8mm-08), I came to some understanding that one doesn't usually get if one simply "assembles factory parts". One of tidbits of information that 'came' to me was that the bolt actually locks up "in" the barrel, not the receiver. Of course it's not really the barrel in a technical sense, but since the barrel extension is conceptually the "barrel", the bolt does lock up in the barrel.

    That illustrated clearly that the barrel nut does NOT have to 'hold' any of the pressure generated by the firing of a cartridge. (Probably. I'm still mulling over the "push me/pull you" of the bolt lockup/barrel extension assembly.) However, that realization quickly lead to "What if the barrel nut did in fact "hold" the pressure"?

    There is more to the question that simple curiosity. I was considering, (but abandoned at this point), making what is essentially a 'Savage-type' barrel attachment mechanism on a milsurp Mauser action - (Turk '38). However, unlike the Savage, the idea was to make the barrel stub 'slick' and cut a flange (slick and flanged like the barrel extension on an AR); thread the OD of the Turk rcvr to accept an AR barrel nut (1 7/16"-18); slip the barrel in the rcvr, screw on the barrel nut and matching handguard, and achieve what I want which is a completely cantilevered barrel. Thinking that process through is what got me to the realization of "in-the-barrel-lock-up" which then lead to "Uh oh, the barrel nut threads are going to have to 'hold' the barrel on, and I don't think that's 'good'". I suspect that Savage's barrel nut attachment assembly maintains the threaded barrel BECAUSE the bolt does not lock up IN the barrel, but that's just speculation on my part. It could simply be for "lawyer" reasons.

    Considering all of the several factors involved, I have essentially abandoned the idea for the Mauser receiver. Even making a custom, steel "barrel nut" does not give me sufficient confidence that the fundamental design is sound in the context of STRENGTH. HOWEVER, I CANNOT FIND THE SPECS TO PUT THAT IDEA COMPLETELY TO REST AND I HATE "GUESSING". So I come here asking for information on:
    1) the tension strength of the "screw joint" between the barrel nut and upper receiver specifically, and
    2) the tension strength between a 1 7/16 - 18, STEEL thread (like the aluminum receiver of an AR-10), and its mating female STEEL nut, (like the aluminum AR-10 barrel nut).

    Here's another important detail: The steel-on-steel joint would only get 0.5" of that 18-pitch thread.

    Let me make some things clear:
    1) Spare yourself the trouble of advising me not to do this for "safety's sake". I have no intention of "doing" this at this point. That does not change my curiosity about the strength of the joint, AND it does not show me where to go to get the information I need.
    2) Spare yourself the trouble of advising me about the "inherent weakness" of Turk '38 Mauser actions. I know better from considerable personal, first-hand experience.

    My real interest is in finding out just how strong the "connection" is between a "real" AR-10 upper and the barrel nut; how much stronger that connection would be if it were steel on steel instead of aluminum on aluminum; and where I can go to either find the information in a table, or calculate it.

    Thanks in advance,
    Paul

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    Overthinking and wasting time.

    Tension strength of threads can be found/calculated in various tables. Google it.. Aluminum thread will most likely be the weaker, on a mixed material connection.

    AR's (and some quick change barrel bolt guns)are made, that simply clamp barrel and barrel extension in upper, with 2 Allen head bolts. No threads at all.

    Robinson M96 barrel and locking extension, is retained by a small spring loaded latch pin, for quick barrel change. Pin engages hole in barrel extension.

    Connection to upper, needs only to handle cycling force of action (low on bolt gun) and keep barrel steady.. And with military rifles... the abuse Bayonet drill, puts on barrel nut to upper interface.

    I have seen several hundred M16's with loose barrel nuts.. Rifle still functions fine.. Front sight tends to flop a bit side to side though.

    Not a big fan of AR barrel assy system. I have seen barrel extensions loosen on barrel, on a FEW M16's.

    More important is HOOP strength of barrel around chamber.

    AR barrels are threaded like normal barrels, the barrel extension is screwed on and pinned

    After working on thousands, I have not seen any fail (in normal use, a cleaning rod left in bore is different).. Even a 800 ft drop during a Parachute incident only bent barrel and upper.

    All the barrel nut on a Savage does, is lock barrel in place (to keep headspace correct). You could ( I would not ) shoot the rifle with no nut. Barrel would be free to twist, and floppy in receiver.. Yes the barrel threads alone are ample. Dan Wesson revolvers use only a very fine shallow thread, to retain .44 revolver barrels.

    Back to hoop strength.. Too thin of a chamber, will swell or burst.. One reason small ring Mausers are considered weaker. Smaller thread, thinner chamber wall..

    The weak point on all actions is the cartridge case, ~62,5 kpsi... yields ~52.5 kpsi brass, which is not fully supported at base.

    Cartridges grip chamber walls during firing, reducing back pressure on bolt.

    Powder gases can only push backwards the inner diameter of case. (for calculating sq in) Shoulder thrust (fairly small amount)has to be added if applicable.

    Rimless cases have an extractor groove. No pressure being applied across groove to speak of...

    I have seen quite a few rifles and belt fed machineguns ruined, when primer pocket split to outside of case, dumping large amounts of gas into action. Bolts held just fine, side of receivers...not so well

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    Quote Originally Posted by abarnsley View Post
    Overthinking and wasting time.
    It's my time, and I'm not particularly 'responsive' to any police, especially thought police.

    Tension strength of threads can be found/calculated in various tables. Google it.
    I did. Instead of snarky answers that aren't answers, how about some links. THAT would be helpful.

    Aluminum thread will most likely be the weaker, on a mixed material connection.
    Duh. That's precisely why I pointed out that I wouldn't be doing that.

    AR's (and some quick change barrel bolt guns)are made, that simply clamp barrel and barrel extension in upper, with 2 Allen head bolts. No threads at all.
    I am, as are many, aware of that. That wasn't the question.

    Robinson M96 barrel and locking extension, is retained by a small spring loaded latch pin, for quick barrel change. Pin engages hole in barrel extension.
    Again, I'm not looking for "another solution", and I thought I made that clear.

    Connection to upper, needs only to handle cycling force of action (low on bolt gun) and keep barrel steady.. And with military rifles... the abuse Bayonet drill, puts on barrel nut to upper interface.
    Doesn't address the question(s), only offers your "solution" to your problem, not mine.

    I have seen several hundred M16's with loose barrel nuts.. Rifle still functions fine.. Front sight tends to flop a bit side to side though.
    I have too, but not "several hundred". "Loose barrel nuts" are neither a concern nor any part of the question.

    Not a big fan of AR barrel assy system. I have seen barrel extensions loosen on barrel, on a FEW M16's.
    Exactly what does that have to do with the question of the strength of the threads in aluminum and steel?

    More important is HOOP strength of barrel around chamber.
    Couldn't agree more, but still doesn't answer the question of thread strength.

    AR barrels are threaded like normal barrels, the barrel extension is screwed on and pinned.
    It is NOT pinned. That pin DOES NOT extend into the threads. It is SOLELY for indexing gas system components and sight. Ida thunk someone that has "worked on thousands" would have known that.

    After working on thousands, I have not seen any fail (in normal use, a cleaning rod left in bore is different).. Even a 800 ft drop during a Parachute incident only bent barrel and upper.

    All the barrel nut on a Savage does, is lock barrel in place (to keep headspace correct). You could ( I would not ) shoot the rifle with no nut. Barrel would be free to twist, and floppy in receiver.. Yes the barrel threads alone are ample. Dan Wesson revolvers use only a very fine shallow thread, to retain .44 revolver barrels.
    Which was my point, but doesn't answer the question.

    Back to hoop strength.. Too thin of a chamber, will swell or burst.. One reason small ring Mausers are considered weaker. Smaller thread, thinner chamber wall.
    "Considered" being the operative word.

    The weak point on all actions is the cartridge case, ~62,5 kpsi... yields ~52.5 kpsi brass, which is not fully supported at base.
    I didn't really ask for a lesson on firearm construction. There was a specific question about thread strength.

    Cartridges grip chamber walls during firing, reducing back pressure on bolt.
    Ditto.

    Powder gases can only push backwards the inner diameter of case. (for calculating sq in) Shoulder thrust (fairly small amount)has to be added if applicable.
    Ditto.

    Rimless cases have an extractor groove. No pressure being applied across groove to speak of...
    Ditto.

    I have seen quite a few rifles and belt fed machineguns ruined, when primer pocket split to outside of case, dumping large amounts of gas into action. Bolts held just fine, side of receivers...not so well
    I'd say thanks for your time, but there was lotsa wasted time and overthinking, (see your first sentence), since the question asked wasn't answered and a lotsa 'stuff' unrelated to the question and some of which was wrong, ("pinned" barrel extensions), was added.

    "Answering" a question with "go look it up" is NOT answering the question, and assumes a great deal about the person asking the question.

    You will probably be offended by my response to your response. I'd say turnabout is fair play.

    Paul

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    My real interest is in finding out just how strong the "connection" is between a "real" AR-10 upper and the barrel nut; how much stronger that connection would be if it were steel on steel instead of aluminum on aluminum; and where I can go to either find the information in a table, or calculate it.

    You can probably find the math in Machinery's Handbook. It's filled with that kind of info.

    As you know, the barrel extension retains the bolt and the firing forces and the barrel nut retains the barrel assembly in the upper. It gets tightened to 70 ft lbs (?). That joint is subject to handling forces and recoil forces of barrel/bolt against the upper but that does not tend to open the joint.

    In a Mauser, the receiver threads perform both functions. In a Savage, the barrel nut is simply a lock nut to keep the barrel from unscrewing while making headspacing easier.

    With a steel upper and a steel nut, you could torque it tighter but why would you need to do that unless you change the design?
    Last edited by GGaskill; 07-11-2018 at 08:33 PM.

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    That illustrated clearly that the barrel nut does NOT have to 'hold' any of the pressure generated by the firing of a cartridge. (Probably. I'm still mulling over the "push me/pull you" of the bolt lockup/barrel extension assembly.) However, that realization quickly lead to "What if the barrel nut did in fact "hold" the pressure"?
    The bolt is 'captured' by the breech of the barrel nut. Therefore, upon firing, the force of expanding gas and the movement of the bullet cause different parts of the rifle to move in different directions. The force of the expanding gas "pushes" in every direction. Some of that force pushes the bullet into the barrel and down the bore. Some of that force pushes the case back into the bolt face. The force pushing the bullet down the barrel also pushes the barrel INCLUDING THE BARREL EXTENSION "out" (FORWARD) of the upper receiver. HOWEVER, because the barrel extension captures the bolt head, the rearward pressure of the back of the bolt on the front of the breech of the barrel extension "pulls" the barrel and extension REARWARD. It cannot be assumed that these forces are "equal" because of different surface areas upon which those forces work: i.e. the case head vs the base of the bullet are only TWO that are not of equal area.

    Ignoring the "push me/pull you" dilemma for a moment, let's assume that there was no barrel nut AT ALL. Would the 'captured' bolt head (remember, this is NOT A GAS OPERATED ACTION) prevent the barrel from "shooting off"? I think so, and here's the reason why: The barrel is threaded into the barrel extension and the bolt is "holding on" to the barrel by virtue of being "captured" by the barrel extension. Therefore, for the barrel to "shoot off", 1) the bolt would have to fail, or the threads between the barrel extension and the barrel would have to strip.

    NOW, given the assumption that the barrel nut does NOTHING to hold the barrel onto the upper when the rifle is fired, (I don't believe it does "nothing" during firing, but for this discussion, we'll assume that), the strength of the barrel nut/upper receiver 'joint' is relatively immaterial and it can therefore be "weak", at least in the context of firing an AR and 'worrying' about shooting the barrel "off".

    JUST HOW WEAK IT IS, is the question.

    Now to the Mauser: I know that the nut on a Savage is only for ease of setting headspace. I know that the threads on the barrel, into the receiver, hold the barrel on the receiver during firing. THAT'S NOT THE QUESTION. The question is: WHAT IS THE STRENGTH OF STEEL THREADS OF SIZE 1 1/16 - 18 WHEN CONTACT IS ONLY 0.50"? The question is NOT derived from trying to imitate the Savage. The question derives from SLIPPING a barrel INTO the Mauser receiver ala an AR, WITHOUT CAPTURING THE MAUSER BOLT HEAD, and holding the barrel ON during the firing process. I'M NOT GOING TO DO THAT, BUT I would like to know the strength of the threads to "hold" the barrel on in the face of AT LEAST 60,000 PSI. There's no "headspace" issue. There is no "I am going to do this". There is no question of how an AR "works" nor how a Mauser "works". I thought the question was simple:

    WHAT ARE THE STRENGTHS OF THE THREADS IN ALUMINUM AND STEEL FOR 1 7/16 -18 with 0.50" of thread contact?

    If this was "so easy" to find/calculate, why is it 6 days after the original post and hundreds of views, and still no answer other that "look it up"? Clearly, it is NOT "so easy" to find or calculate, or someone would have done the "easy" thing. And that is precisely why I started this thread.

    My intention is neither to be rude or insulting. However, I am reminded of so many of my college classes in which the professors explained grand theories, but when pressed for PRACTICAL details, responded with "the rest is just algebra", or "we'll ignore air resistance" (or whatever detail he COULDN'T account for), or the response I hated the most: "look it up", which was both arrogant and lazy.

    Paul

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    We have test fired M16/M4 uppers without the barrel nut in place. If the gas tube is removed there is no movement. With an operating gas system, the barrel assembly will try to move forward slightly. This is all done on high speed video.

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    Quote Originally Posted by gitano View Post
    If this was "so easy" to find/calculate, why is it 6 days after the original post and hundreds of views, and still no answer other that "look it up"? Clearly, it is NOT "so easy" to find or calculate, or someone would have done the "easy" thing. And that is precisely why I started this thread.
    Took me about 5 min to find this data:
    https://www.fastenal.com/content/fed...s%20Design.pdf (thread stripping formula on page 6)

    Unified Screw Threads, Standard Series (thread info required for above formula)

    The only thing missing is the shear strength of the material you want to consider, which you then multiply by the answer to the formula in the fastenal pdf. Is that good enough of an answer, or do you want me to do the math for you? I'm not being sarcastic... give me the exact material that you are considering and I'll do the math.

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    Quote Originally Posted by MilGunsmith View Post
    We have test fired M16/M4 uppers without the barrel nut in place. If the gas tube is removed there is no movement. With an operating gas system, the barrel assembly will try to move forward slightly. This is all done on high speed video.
    Cool! Nothing beats hands-on testing!

    Thanks!

    Paul

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    Quote Originally Posted by Royldean
    Took me about 5 min to find this data:
    https://www.fastenal.com/content/fed...s%20Design.pdf (thread stripping formula on page 6)

    Unified Screw Threads, Standard Series (thread info required for above formula)

    The only thing missing is the shear strength of the material you want to consider, which you then multiply by the answer to the formula in the fastenal pdf. Is that good enough of an answer, or do you want me to do the math for you? I'm not being sarcastic... give me the exact material that you are considering and I'll do the math.
    No-thanks, I can do the math myself. That was precisely the simple answer I was seeking.

    Thanks!

    Paul

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    Just to close the loop:

    Using this calculator (https://www.engineersedge.com/calcul...shear-area.htm) I get a factor of 1.19911 for 1 7/6-18, class 2b EXTERNAL threads.
    Using this calculator (https://www.engineersedge.com/calcul...shear-area.htm) I get a factor of 0.84862 for 1 7/6-18, class 2b INTERNAL threads.

    From this page: ASM Material Data Sheet I read a value of 83 kPSI for 7075 aluminum.
    From this page: AISI 4140 Chrome-Molybdenum High Tensile Steel I read a value of 135 kPSI for TEMPERED 4140 steel.

    Assuming the "weak link" to be the smaller of the two values, I get 0.84862 * 83000 = 70,435 PSI for 7075 aluminum, and
    0.84862 * 135000 = 114,564 PSI for TEMPERED 4140 steel.

    1) Does anyone see a math error or get different numbers?
    2) Assuming my results are correct, the 'safety factor' for tempered 4140 steel is almost a factor of 2 based on the ANSI standard of 60,191 PSI for max chamber pressure for the .308 Win. This has been my experience with engineering specs when "life and limb" are a consideration.

    I know that the AR-10 upper receiver is not 4140 steel. I know that a Turk '38 Mauser receiver is PROBABLY not 4140 steel. Again, I am NOT "building" this. My use of the .308 Win "yardstick" was to put the failure values in the context of a common rifle cartridge and its ANSI max chamber pressure in the "average" bolt action rifle.

    Thanks for the assistance.

    Paul

    PS - Just realized that the above calculated numbers use the diameter and pitch values of an AR-10 upper, not a "regular" bolt action rifle. Therefore, the safety factor will be different. Whether that difference is significant I will leave to those interested in that information to calculate.

    Paul

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    Paul

    I looked at the calculator page, but my ad blockers put warning notices all over the page, so I didn't use the interactive program.

    May we assume that the "factors" are in square inches of metal that would need to fail? (Thread shear area) That combined with shear strength of the materials (in psi) would be
    pounds /inch X inch, all over inch X inche. The result is a POUNDS term rather than the psi term you have posted.

    so

    70,435 lbs load for the alu
    114,564 lbs for the Steel.

    Calculating the chamber pressure in psi X the cartridge base area (pi xR^2) would be in units of psi / square inch. for a compatible LOAD value in lbs.
    (Note the chamber pressure is NOT applied over the entire shell base, only the internal area.)

    The area terms must fall out, and the load terms (lbs) may be compared and any safety factor be applied.

    eta

    Also note this comment:
    "First, unlike tensile and yield strengths, there are no published shear strength values or requirements for ASTM specifications. The Industrial Fastener Institute (Inch Fastener Standards, 7th ed. 2003. B-8) states that shear strength is approximately 60% of the minimum tensile strength."

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    Default Calculating Threaded Connection Barrel Assembly on the AR10

    Quote Originally Posted by gitano View Post
    I'm not a person inclined to "leave well enough alone". (However, I do believe strongly in "Don't fix what ain't broke".)
    I'm also not stupid or foolish. (I have made it to 64 with all my parts and faculties in spite of starting to reload when I was 16, and starting to making rifles when I was 50.) So...

    While building another AR-10-based wildcat (this one chambered in 8mm-08), I came to some understanding that one doesn't usually get if one simply "assembles factory parts". One of tidbits of information that 'came' to me was that the bolt actually locks up "in" the barrel, not the receiver. Of course it's not really the barrel in a technical sense, but since the barrel extension is conceptually the "barrel", the bolt does lock up in the barrel.

    That illustrated clearly that the barrel nut does NOT have to 'hold' any of the pressure generated by the firing of a cartridge. (Probably. I'm still mulling over the "push me/pull you" of the bolt lockup/barrel extension assembly.) However, that realization quickly lead to "What if the barrel nut did in fact "hold" the pressure"?

    There is more to the question that simple curiosity. I was considering, (but abandoned at this point), making what is essentially a 'Savage-type' barrel attachment mechanism on a milsurp Mauser action - (Turk '38). However, unlike the Savage, the idea was to make the barrel stub 'slick' and cut a flange (slick and flanged like the barrel extension on an AR); thread the OD of the Turk rcvr to accept an AR barrel nut (1 7/16"-18); slip the barrel in the rcvr, screw on the barrel nut and matching handguard, and achieve what I want which is a completely cantilevered barrel. Thinking that process through is what got me to the realization of "in-the-barrel-lock-up" which then lead to "Uh oh, the barrel nut threads are going to have to 'hold' the barrel on, and I don't think that's 'good'". I suspect that Savage's barrel nut attachment assembly maintains the threaded barrel BECAUSE the bolt does not lock up IN the barrel, but that's just speculation on my part. It could simply be for "lawyer" reasons.

    Considering all of the several factors involved, I have essentially abandoned the idea for the Mauser receiver. Even making a custom, steel "barrel nut" does not give me sufficient confidence that the fundamental design is sound in the context of STRENGTH. HOWEVER, I CANNOT FIND THE SPECS TO PUT THAT IDEA COMPLETELY TO REST AND I HATE "GUESSING". So I come here asking for information on:
    1) the tension strength of the "screw joint" between the barrel nut and upper receiver specifically, and
    2) the tension strength between a 1 7/16 - 18, STEEL thread (like the aluminum receiver of an AR-10), and its mating female STEEL nut, (like the aluminum AR-10 barrel nut).

    Here's another important detail: The steel-on-steel joint would only get 0.5" of that 18-pitch thread.

    Let me make some things clear:
    1) Spare yourself the trouble of advising me not to do this for "safety's sake". I have no intention of "doing" this at this point. That does not change my curiosity about the strength of the joint, AND it does not show me where to go to get the information I need.
    2) Spare yourself the trouble of advising me about the "inherent weakness" of Turk '38 Mauser actions. I know better from considerable personal, first-hand experience.

    My real interest is in finding out just how strong the "connection" is between a "real" AR-10 upper and the barrel nut; how much stronger that connection would be if it were steel on steel instead of aluminum on aluminum; and where I can go to either find the information in a table, or calculate it.

    Thanks in advance,
    Paul
    I believe the basic formula would be (("pi" 3.14159)x(minor diameter of thread in inches)x(1/thread pitch)x(material allowable shear stress in psi)x(number of threads that are fully seated))/(safety factor, I would use 10 min.). This will get you close to a working load limit. Someone verify my math before loading up the battery and firing...LOL...

    So an example calculation would look like this: (3.14159)x(1.41" approx. minor diam. of 1-7/16" threads I think)x(1 inch/18 threads per inch)x(say 24,000 psi allowable strength)(say 8 threads or so)/(10) = 4,724 lbs. working capacity

    From here you would have to transform the working pressure in the system into a force on the barrel connection by working up some sort of active "area" that the pressure gases would push against in the breech. That could be tricky and not sure about the proper technique in obtaining the correct working area. Perhaps that working area would be simply the cross sectional area of the bullet. So pressure in psi x area in sq. inches = a force in lbs. to compare to the calculated strength of the barrel connection from before.

    This is my opinion, and this should get you close enough for research purposes. Any fabrication would need a bit of safe and hopefully "non-destructive" testing in the lab. haha...

    Good luck with your quest for information.

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    Thanks for taking the time to reply, pantherpaw9. That looks like a good place to start. I'll let you know what I come up with.

    Paul

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    okay, probably demonstrating my ignorance here, but when I rebarrel a Mauser, I cut the thread shoulder so that it contacts the C ring about 0.002 before the shoulder contacts the receiver. Then, when I torque the barrel, the shoulder/receiver has zero clearance, the barrel face is fully seated on the C ring, and the threads are essentially loaded in both directions.

    At this point, when the weapon is headspaced correctly, the only significant forces it should be seeing are radial and largely contained in the receiver/barrel, and, to a far lesser extent, longitudinally on the bolt face.

    Ackley showed eloquently that one could pretty much cut the lugs off of a well-chambered rifle, and because of the engagement of the cartridge with the chamber, there were pretty negligible forces exerted on the bolt.

    It seems to me, that trying to use the Savage model of adjustable headspacing, (where there's also not a C ring in the way) is likely to be difficult on a Mauser action...

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    "the Savage model of adjustable headspacing..." isn't the goal or even desireable. (Don't get me started on "headspace". A bigger paper tiger is not known to Western civilization.)

    I have Ackley's books, and I don't recall him experimenting with "cut off lugs". Doesn't mean he didn't. I just don't remember that. If you could supply a chapter, I'd appreciate it.

    That said, standard physics says that pressure will be uniform per unit area on the "wall of the case". The wall of the case includes the "head end" of the case. The area of the head (in square inches) times the max pressure (in pounds PER square inch) is the max "bolt thrust" in pounds. (The "other end" of bolt "thrust" is the "thrust" on the butt of the bullet.) The actual force on the bolt can vary due to poor "case grab" (as you point out in the converse), or by 'lubing' the case. The case does indeed "hold" about 10,000 PSI (according to current opinion), of the max pressure, BUT... the most common reason for head separation is that the case walls actually DO "grab" the chamber wall, and the bullet goes out the front and the head HAS to move "backward" until it meets the bolt face (taking up the head SPACE). If the headspace is too large, the case can't stretch enough and it separates in front of the web. A good (proper) fit of the reloaded case to the chamber minimizes case stretch, BUT... the case still has to "hold" the max pressure up to its yield strength (which is about 10,000 PSI). Beyoind that point, the chamber, including the bolt, HAS to hold the rest of the pressure. The bolt is just the other end of the "system" from the bullet.

    "It seems to me, that trying to use the Savage model... is likely to be difficult on a Mauser action..."
    Fair enough.

    Paul

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    Sure: Here's a quote referencing the experiment I'm talking about (I'm at work and the anti-gun firewall is up, of course)


    ...Parker Ackley was a well known gunsmith located in Salt Lake City in the late 50's and into the 60's. He wrote several books, one of which was "Volume One: Handbook for Shooters & Reloaders". His specialty was the development of wildcat rifle calibers which he created and tested and built rifles for. He was also a contributing gunsmithing editor for "Guns and Ammo Magazine" for a number of years. In the handbook I mentioned above in a chapter entitled "Pressure" (page 138 and following), he talks about an experiment he did with an old Model 94 Winchester. Briefly, he removed the locking lugs from the action. Then he rechambered the barrel for his 30-30 Improved (less taper to casing walls than a standard 30-30). With the lugs removed from the action, he fired two standard factory .30-30 cartridges. Prior to shooting, he made sure that the chamber was clean and dry. The rounds he fired formed to the Improved chamber perfectly with no primer back out. Then he unscrewed the barrel one turn and fired two more rounds. The primers backed out equal to one barrel thread, but the cases did not back up against the bolt, which means that the brass case withstood the pressure. Two more factory cartridges were lightly oiled. The primers did not back out, but the shoulders of both rounds were blown forward the distance of one barrel thread. Thus the oiled cases did not adhere to the chamber walls but backed up against the bolt face. Last, he unscrewed the barrel two full turns and cleaned and dried the chamber. He fired two more factory rounds. The 1st casing remained tight in the chamber but the primer fell out. (He lengthened the firing pin to fire the rifle). He then oiled the case of the second round and fired it. The casing stretched and separated just above the base, indicating that it again did not grip the chamber walls and expanded back to the bolt face until it separated. He felt that this experiment proved that a clean, dry chamber will allow a cartridge case to grip the walls of the chamber and not move back against the bolt face in most cases, making the actual back-thrust pressure on the bolt face itself little or none. I think it is the back thrust of the casing on the bolt face, then to the toggle lock-up, that is the pressure we should be concerned about. The actual chamber pressure means nothing (if it is a safe load to begin with) as the barrel and receiver ring area contains all of that pressure itself.
    If that's inadequate, I can get chapter and verse when I get back to my library.

    This is from the Brownells website which, for some reason isn't blocked:

    ...On the average bolt rifle, you establish correct headspace by lathe-turning the shoulder on the barrel. However, with the Savage, all you have to do is remove the firing pin and ejector from the bolt, insert a GO Headspace Gauge into the chamber, screw the barrel into the receiver until the gauge bumps up tight against the bolt face, tighten the barrel lock nut and you have a barrel that is set up to minimum headspace.
    That would be the Savage headspace adjustment that isn't the goal, or even desirable...

    Regards,

    JJK

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    Thanks for the reference! That's perfect.

    I'm just not interested or concerned about headspace.I own a couple of Savages with that design and I don't bother to use it to set the headspace except 'close enough'. I make minute ("my noot") adjustments for headspace with my reloading dies for all my rifles, including the Savages.

    Paul

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    Happy I could help.

    I build a lot of 22-250s, and, especially with big bullets and fast twist, headspace really seems to mean a lot off the bench.

    I have a bunch of uncut bolt face Mauser bolts, a plethora of Steyr actions, and I'm thinking of expanding my horizons into other little (but heavy) bullets with big shoulder-indexed cases...

    I'm very interested in your perspective and experiences.

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    My 'issue' isn't technically with headspace per se. More correctly put, it's with people that think headspace is in any way associated with "safety". Those people that essentially say that civilization as we know it will end if you shoot a rifle with "excessive" headspace. While, at the same time extolling the 'virtues' of "fireforming" cases for wildcat chambers.

    Back at the turn of the 19th century, when bolt actions were first becoming widely used, AND following an era where "cartridge" cases were fabricated by wrapping strips of brass and copper around a mandrel, "gasses" were important. In military firearms especially, if a case came apart in the chamber, the soldier shooting the rifle could be harmed and the rifle could be taken out of commission. (Let's not get confused that the powers that be were concerned about the soldier in any other way than "reduced firepower".) When original military rifles started using cartridges loaded with "nitro-cellulose" (meaning higher chamber pressures), if the case head separated due to excessive headspace, the gasses usually went directly into the soldier's face. The military "learned", and CHANGED THE DESIGN OF THE ACTION so that "escaping" gasses were directed down or sideways out ports built into the action FOR THE PURPOSE of deflecting "errant" gasses. That put an END to ALL DANGER associated with cases coming apart and gasses coming BACK TOWARD THE SHOOTER. THE END. PERIOD. OVER. DONE. NOT AN ISSUE.

    Now, when I bother to get up on my hobby horse about the DANGER of "excessive" headspace, I usually get called names and accused of being "The kind of person that is a danger to everyone at the rifle range". At best. Let me be clear:

    1) There's no good reason for owning a rifle with INCORRECT headspace - excessive or otherwise.
    2) PROPER headspace is the sign of a properly skilled machinist or gunsmith.
    3) PROPER headspace increases case life. For those that don't reload, this is a COMPLETELY MOOT issue.
    4) "Excessive" headspace is TRIVIALLY addressed (and ELIMINATED) at the reloading press.
    5) The VAST majority of fear-mongering associated with headspace is either ignorant people parroting BS that is 100+ years old, OR (and this is the more common circumstance), IT IS SIMPLY A WAY OF PARTING PEOPLE FROM THEIR MONEY BY DEMANDING THAT THEY TAKE THEIR RIFLE TO A "QUALIFIED" GUNSMITH TO "CORRECT" THE DANGEROUS SITUATION. THAT INFURIATES ME!

    There ARE a VERY FEW circumstances where, in MODERN arms, headspace is an "important" issue. With the widespread love affair by young American shooters with semiautomatic rifles of military design, (yes, I mean AR-15s etc.), proper headspace is critical to proper funcioning of the rifle in semi-auto or automatic operation. And STILL, it's NOT an issue of DANGER to the shooter OR to anyone near the shooter.

    I shoot most of my cases until they ALMOST separate their heads. Occasionally, a head separates. Since I NEVER "load hot", I have NEVER stuck a case, with a separated head, in a chamber. Furthermore, NEVER has a rifle of mine been "harmed" by "escaping gasses" from a separated head. NEVER. In fact, I once accidentally fired a .338 Mauser Ackley Improved cartridge in a .338 Win Mag chamber. There is hardly a way to create more EXCESSIVE headspace than that. "Gas" went "everywhere", EXCEPT my face. It didn't tear up my rifle. It didn't harm the stock of the .338 Win Mag. The x57 Ackley case was severely ruptured from stem to stern in 3 or four places. (I still have a picture of that case if you'd like to see it.) It did NO HARM. I am NOT a competitive target shooter. Were I, I would PROBABLY not run my cases quite as long as I do. But that has NOTHING to do with SAFETY, only COMPETITIVE TARGET SHOOTING precision.

    I'm not inclined to "argue" about the matter. It's too straightforward an issue. There is NO danger, PERIOD, and that is the ONLY "thing" with respect to "excessive" headspace that I give a tinker's damn about. EVERYTHING else associated with headspace (like precision, or "good machining practices",) are a PERSONAL matter as far as I'm concerned.

    I do not concern myself with impressing anyone. Therefore, I add the following information ONLY in the interest of allowing those that read my above comments to have an idea about the person writing them.

    1) I'm 67 years old.
    2) I started reloading at my 16th birthday when I received my first Lee Loader for my .270 Win.
    3) I started making rifles (not assembling parts) when I was 49 years old.
    4) I have all my fingers and toes and eyes and have never needed to go to the emergency room for anything associated with civilian firearms shooting.
    5) No one has ever been harmed by my reloading.
    6) No firearm has ever been harmed by my reloading.
    7) I have personally built (not assembled parts) about 2 dozen rifles, all but one or two of them chambered for wildcat cartridges.
    8) All the rifles I have built have functioned as designed and no one has ever been harmed in any way by shooting them or the ammo I have reloaded for them.
    9) Every rifle I have built, except one, has shot better than 1 MoA out to 300 yards. 300 yards is my personal maximum range for hunting, and better than 1 MoA is my personal precision standard.

    You asked for my perspective and experiences - there ya go.

    Paul

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    Quote Originally Posted by gitano View Post
    My real interest is in finding out just how strong the "connection" is between a "real" AR-10 upper and the barrel nut; how much stronger that connection would be if it were steel on steel instead of aluminum on aluminum; and where I can go to either find the information in a table, or calculate it.

    Thanks in advance,
    Paul
    Isn't there a "rule of thumb" that suggests that 5 full threads of any "good" threaded assembly EXCEEDS the tensile failure of the threaded material? Or was that 3 full threads? I forget.


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