Looking to Build a Bolt Action From Scratch

Hello everyone. I am looking to build a bolt action rifle from scratch off of a custom built action I am designing based off of the Mosin Nagant action to allow me to use my Mosin Nagant parts. :P The rifle will be chambered in 7.62 NATO and will feature a Bartlien or Krieger barrel. My question is what material should I make the action out of? I am planning on 4140 chrome moly. I am curious though, what kind of hardness should I be looking for? Should I buy prehardened 4140 and do all machining from there? I will be EDMing my bolt raceways and was thinking of buying non prehardened material, doing all rough machining and then getting it heat treated and then finalizing the job by EDMing the raceways and finish machining located from the EDMed raceways. I am looking for the highest possible accuracy while still remaining fairly affordable. Any ideas, suggestions or opinions? I appreciate it and am very excited for this build.

What is your Goal? What you are attempting will not be reasonable in price and what accuracy are you wanting to achieve?

Butch Lambert said:

What is your Goal? What you are attempting will not be reasonable in price and what accuracy are you wanting to achieve?

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My goal is to build a modernized Mosin Nagant tactical bolt action that can achieve .5 MOA or better accuracy. I think I should be able to build the rifle for ~$1000. I have access to wire EDM machines and see no reason why this job wouldn't be doable. I am intending to make a new bolt head for the rifle with a .308 bolt face. As long as I make an accurate action with true face and threads as well as accurate bolt races fitted to a high quality barrel hand threaded and chambered in an indicated barrel chambering fixture within .0002 inches I see no reason why this cannot be done. I know the Mosin Nagant design is outdated but there are WWII rifles out there with good bores that get 1 MOA. With a match barrel and everything true as well as a newly machined precision bolt head, I see no reason why .5 MOA is not doable. I like that the Mosin Nagant design is simple and easily field stripped and my version will feature a stronger "hex" receiver design and an integral picatinny rail as well as a Timney trigger and match barrel like a Krieger or Bartlein. Even if the project ends up costing a little more than $1000 I can't imagine it being more than $1200.

As they say, there's no explaining taste. I can think of at least 6 military bolt actions I'd consider making a 'match grade' version of, including a Krag, before a Mosin. Every single one of them I've handled HAD to have the bolt handle smacked with your palm to get them open. Awful, clunky things IMO. Yeah, I know good ones are amazingly accurate, but so are Swede's and Swiss K-31's.

Now, a Krag ... there'd be a project. I was looking at a bare receiver the other day. Stared at it for probably 20 minutes trying to think of how they made that thing back in the 1890's. Awesome piece of work.

The Russians and the Finns both made international 300m target rifles off the Mosin action using the 762x54 round, in addition many people have put good barrels , even surplus heavy machine gun barrels on surplus mosins and achieved sub moa so what your proposing is doable, even without machining your own receiver. However there are other reasons that if your going to build your own action , use other designs. If it were me and I was looking to machine my own action I'd do something that takes a Remington bolt, aics mags, and anschutz triggers with an integral circular lug on the front face of the action that has it's od threaded to accept ar15 free float handguards. Also an integral mount for ar15 buttstock .

akajun said:

The Russians and the Finns both made international 300m target rifles off the Mosin action using the 762x54 round, in addition many people have put good barrels , even surplus heavy machine gun barrels on surplus mosins and achieved sub moa so what your proposing is doable, even without machining your own receiver. However there are other reasons that if your going to build your own action , use other designs. If it were me and I was looking to machine my own action I'd do something that takes a Remington bolt, aics mags, and anschutz triggers with an integral circular lug on the front face of the action that has it's od threaded to accept ar15 free float handguards. Also an integral mount for ar15 buttstock .

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Now that is an interesting idea right there.

wesg said:

As they say, there's no explaining taste. I can think of at least 6 military bolt actions I'd consider making a 'match grade' version of, including a Krag, before a Mosin. Every single one of them I've handled HAD to have the bolt handle smacked with your palm to get them open. Awful, clunky things IMO. Yeah, I know good ones are amazingly accurate, but so are Swede's and Swiss K-31's.

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The reason for that bolt stick is almost always caused by residual cosmoline inside the chamber that every time the rifle is fired melts a little and then hardens slightly and essentially glues the casing into the chamber. If you clean you gun really well this will not happen. When I bought my 91/30, the first time I shot it, it was fine for a few minutes and then started doing exactly what you describe. Took it home and cleaned it really, really well and the next time I shot it, it was smooth as silk the entire time. It is very difficult to remove all of that cosmoline inside the chamber but that is almost always the cause for a sticky bolt. I have only handled about three Mosins personally and only actually shot mine but I have never seen one that had a true stiff bolt. Mine isn't even a nice one. It is a 1942 Izhevsk round receiver with a crappy barrel but it still works flawlessly.

I've built wood stocked hunting rifles with Mauser '98 actions that will quit easily meet your 1/2" accuracy criteria (3 shot groups w/ handloads). I did nothing more than square the face of the action, weld a new bolt handle on and accurately drill and tap for scope mounting, when it came to the metal work. I'd feel like I was wasting my time "making" a Mosin receiver from bar stock or any other method for that matter. But, I guess we used Mausers and Sringfields, back in the day, because they were low priced and good ones were available. I never considered "making" one, not even for fun. There are still many '98s used for custom rifles, today. I've always considered the Mosin to be a good trot line weight as there are so many other actions available that are much more suitable for me to spend my time on. As a human being, I realize I have 'limited time' on this earth and choose to spend that 'time' as wisely as I can. I waste enough of it (time) as it is! Do as you please as your "time" is yours.

tarboxb said:

The reason for that bolt stick is almost always caused by residual cosmoline inside the chamber that every time the rifle is fired melts a little and then hardens slightly and essentially glues the casing into the chamber. If you clean you gun really well this will not happen. When I bought my 91/30, the first time I shot it, it was fine for a few minutes and then started doing exactly what you describe. Took it home and cleaned it really, really well and the next time I shot it, it was smooth as silk the entire time. It is very difficult to remove all of that cosmoline inside the chamber but that is almost always the cause for a sticky bolt. I have only handled about three Mosins personally and only actually shot mine but I have never seen one that had a true stiff bolt. Mine isn't even a nice one. It is a 1942 Izhevsk round receiver with a crappy barrel but it still works flawlessly.

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That's a good thing to check, thanks. But these were unloaded, just dry firing them. My Finn M-39, and a Polish (or Romanian) M-44. And a friend had a couple. All the same. Maybe part of it is the short bolt handle.

Compare to a M-96, Lee-Enfield, or a Krag that open with one finger. Granted, the M-96 and L-E cock on closing. But the Krag cocks on opening, with a long striker fall like every other military bolt action.

Actually, the more I think about it, it was maybe just the last 1/4" of travel where it would hang up. And the easy way past that was to yank them open. I'll have to do some major digging to get to one to try it again.

I suggest that anyone looking for sub-MOA performance do a bit of shooting with a cock-on-closing rifle to see how well these stay on their shoulder when cycling rounds. There's the key to a consistent hold, by golly.

I'm not positive uber-accuracy is a sure bet just because bolt & action faces are trued to .000x", lugs lapped within a micron or two, and "I made it myself" to get everything 'perfect' (, Butch). btw, don't forget mag or follower mods for rimless ammo if not to be single loaded, action bedding, barrel harmonics, etc and your new hobby of reloading. (MNs are 'simple' Krags and SMLEs are smooth.)

Oh, just DO IT!

Most of the Mosin's vertical raceway is easily done with an end mill; the short section in the receiver ring can be pecked out by hand with the tailstock or quill. Beats the heck out of using a rifling head, custom broaches, or EDM.

The traditional horizontal Mauser raceway can't be done with and end mill, which means it's that much more hassle just for the basic receiver.

The Mosin's lower bolt lug assures plenty of area to grab the next cartridge without nosing it down into the front of the magwell. If you copy the Mosin interruptor system, you get a clean feed of any rimmed or rimless cartridge without tedious twiddling of feed lips and internal receiver cuts. Or use a single-stack magazine from an existing rifle. Make sure your donor mag actually has feed lips; some designs are just boxes, with the lips in the receiver.

The basic Mosin receiver approaches a round tube, and can be functionally duplicated with a round bar. Just hang the trigger group off a bracket, weld or clamp a recoil lug, and boogie. Pick a Mauser or Remington 700 trigger pattern and choose complete assemblies from the aftermarket, or take-offs from a gun shop or auction site.

The Mosin's vertical raceway means the bolt lugs turn and lock into the sides of the receiver ring, with solid metal all the way back on the left and the full length of the ring on the right. Horizontal raceway designs generally have the magazine, lower lug, and feed ramp trying to occupy the same space, generally to the detriment of the lower lug. No way that can be as strong as a Mosin's fully-backed lug seats.

The Mosin bolt is a relative of the 1871 Mauser / Vetterli / Lebel designs, and way more complex than it needs to be by modern standards. Some of that was likely due to the "disassemble without tools" requirements various militaries had, and the shape, though complex, had been done several times before and the tooling requirements were well-known. Heck, the Russians probably bought Mauser or Lebel surplus tooling to make them with. I'd just make up an ordinary Remington 700 style bolt and weld the handle on.

Just because the bridge is split doesn't mean you *have* to guide the cocking piece in the slot. Guide it on the bottom as normal and save a bunch of weight.

Cover the bridge slot with a screwed or soldered on cap to contain the rear sight or scope base. Then you don't have to weeble around with three-legged or sidemount scope brackets.

Unless you have some special requirements, there's no reason to use anything other than 4140. Reported Rockwell hardnesses for production rifles are all over the place. Otteson vol.II has figures for some.

- TRX "looked a Mosin once or twice, on a cloudy night"


edit: part of the Mosin bolt's complexity is due to the non-rotating guide lug on the bottom. That could be functionally approximated by making a clip-on lug using Mauser extractor collars. That's basically how some Sako designs add a guide lug.

The desire to spend one's time on such a project is a mystery to me. But, the OP only asked for a recommended steel for his project. Surely, someone can give some guidance on the best , or a suitable material? Regards, Clark

Questions like this frequently appear on these forums. Usually from a low post count or first time poster. I sometimes wonder if the poster is actually looking for a specific answer or just shopping his idea to see what viability it has. The answer to his question is not as simple as naming a steel and hardness number but goes into much deeper knowledge of tha application.

If anyone is so bold as to put forth an answer, the chances are very good that three other posters will immediately reply with counter information, insulting the responder's and each other's intelligence and parentage, leaving the OP with four opinions, none of which may be of any value. From the little time I spend on this forum, I suspect that two or three gents are just waiting for someone to step forward.

There is a lot of basic engineering information on design and material strength and the parameters involved in the building of rifle actions. I recommend any with intentions of designing and scratch building an action to seek this information and run the numbers for himself. He will be dealing with tens of thousands pounds of pressure a few inches from his face and eyes and will be better served to actually learn how to calculate and specify the materials himself than to count on some guy on the internet.

precision tools said:

The answer to his question is not as simple as naming a steel and hardness number but goes into much deeper knowledge of tha application.

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Yeah, so 4140 Ph would be perfect. Or how'bout 8620 with a color case. What the hell, some say 7075 t6 is as strong as mild steel; M4 does it, so use that!

All kidding aside, sign up for homegunsmithforum and you will see some examples from others that have put in the 500 hours that you are proposing.

tarboxb said:

Hello everyone. I am looking to build a bolt action rifle from scratch off of a custom built action I am designing based off of the Mosin Nagant action to allow me to use my Mosin Nagant parts. :P The rifle will be chambered in 7.62 NATO and will feature a Bartlien or Krieger barrel.

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Not what I would choose... But not my project either! Moving on...

tarboxb said:

My question is what material should I make the action out of? I am planning on 4140 chrome moly.

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Based on the specs. of 4140, the wide selection of conditions it is available in and the overall availability, 4140 is the only alloy steel I have ever used. That is not to say there aren't other good choices... There are.

tarboxb said:

I am curious though, what kind of hardness should I be looking for?

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High 20s to mid-30s Rockwell C works well. Much harder than that can lead to ductility issues. I used to use Rhc 35 for everything and have never had a problem. However, after some people suggested that there was a risk of galling using steel of the same hardness for the action and the bolt head I switched to using Rhc32 for the bolt head and Rhc35 for everything else.

tarboxb said:

Should I buy prehardened 4140 and do all machining from there?

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I do. I find annealed 4140 to actually be more difficult to cut and provides a sub-standard finish. Further, I don't see the point of roughing the part, having the piece hardened and then setting up the part a second time to finish it. Setup is a BIG part of firearms work. Why do it twice unless there is a good reason?

tarboxb said:

I will be EDMing my bolt raceways and was thinking of buying non prehardened material, doing all rough machining and then getting it heat treated and then finalizing the job by EDMing the raceways and finish machining located from the EDMed raceways.

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Although you can do it this way, see my comments above, I see no point to it. I have ZERO issues working pre-hardened (Rhc35) 4140. In fact I the Rhc35 for even the parts that don't "require" hardening. Bolt shrouds, trigger guards... They come off the machines with a better finish than if U had used annealed 4140. HSS tooling works very well with good coolant flow to the cutter. I use TiAlN coated carbide cutters and NO coolant for faster cutting on the mill. But I am also working with a CnC Bridgeport. On a manual machine, mill or lathe, HSS w/ coolant and slower feed rates would be a better combination.

tarboxb said:

I am looking for the highest possible accuracy while still remaining fairly affordable.

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LoL! Building your own will cost you more than you think! And by orders of magnitude! There are lots of reasons to build your own bolt action. By the time you get done with the tooling, fixtures, jigs, and equipment you need to build a proper bolt action you could buy a very nice action pre-made by someone how is far better at it than you will be your first time out. I'm not trying to discourage you. I'm just trying to help you walk in to such a project with your eyes wide open.

tarboxb said:

Any ideas, suggestions or opinions? I appreciate it and am very excited for this build.

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My "suggestions" ARE "opinions"... The same as anyone and everyone here. Use opinions at your own risk. Research EVERY THING for your self from as many different sources as you can. Thous who have done this more than once have found things that work for us. That does not mean that my way is the best way. I'm just in a place where I know I can get the results I want repeatably. You will find what works best for you.

If you decide to move forward with 4140... McMaster-Carr has several flavors of 4140 ranging from annealed to Rhc35 and an ETD-150. Any of them could find it's way into a well executed design.