? barrel straightness - v blacks & indicator ?

[permatex]

Hi, hopeing to get some advice. Taken a rifle barrel, put a V block near each end, w/ dial indicator in middle, to check for straightness. Getting a consistant high and low difference when twisting barrel. Anyone done this, and what what be considered acceptable and not, or what were your results? The idea is straightness and accuracy. Thank you

 

[henrya]

There could be (and has been) lots written about this subject. Of course you’d want the barrel to be perfect inside and out, but its not. Some people index for straightness - have the barrel screw in, tighten and have the run out up or down. Really good barrels are generally on average better than poor barrels.
The generally agreed upon thought is that the bullet must be perfectly aligned with the bore, but that’s on the inside of the barrel. Outside will matter less. Buying your barrel from a top maker is the best way to get the finest accuracy. After that its a bit of a gamble, but much less of a gamble than a cheap barrel.

 

[L Vanice]

In the 1950's I read a book on one of the early 19th century American long gun makers. I recall that the barrel straighteners sighted through the bore on a wire stretched tightly across a window in the shop to detect bends in the barrels. That was long before dial indicators were available and is a reminder that there are often simple-seeming solutions to problems that were developed by practical mechanics working with what was available to them. Often, old ideas that worked before will still work.

Larry

 

[hawkfan9]

There is a lot of information to read about rifle barrels. They aren't straight. Neither are the bores. What matters is, as already stated above, the chambering of the cartridge in alignment to the bore. Great pains are taken when threading and chambering a barrel to align it in the lathe concentric to the bore, not the OD. The most accurate barrels are aligned to less than a tenth, and then actions are blue printed, given a diet, and the threads are cut in similar alignment to concentric of the bolt. This way, when the barrel is threaded into the action, everything is as aligned as it could be. Also, the better barrels are hand lapped so the bores are properly and equally sized the length of the barrel, so the rifling comes into contact and twists the bullets with equal pressure around all sides. This will give you your most accurate shooting barrel. I just purchased a carbon fiber barrel from Proof Research for a hunting rifle, and the bore is as smooth as a mirror, except for the rifling, of course. It appears completely polished. 3 shot groups at 100 yards are all touching, and it's not even broken in yet. In the neighborhood of 1/4 to 3/8's MOA. You get what you pay for.....lots of GREAT barrel makers out there, and plenty of also ran's, as well. Of course, it has to be chambered properly, with a reamer that isn't worn out, too.

 

[john.k]

Ive seen a great many barrels ,new and used ,that had runouts of the external form of as much as .012"TIR...........the simple way of checking the internal bore for straightness is with short rods ground to slightly under bore dia , maybe 1/2 thou under ......one rod will be 1/2" long ,the other 6" long .....the first rod checks for bore diameter regularity ,the second rod checks for straightness.......both rods should be a light,even push thru the bore..........From before WW2 ,the arms factories had electronic bore straightness gauges for finish rifled barrels............No doubt most here have heard of the famous "Star Gauge " used by Springfield Arsenal for checking bores .

 

[moosesgunsmithing]

Are you indicating off the bore or the OD? I haven't found a lack of straightness to really matter, just concentricity of chamber, threads, and crown.

Also, you may just have bad v blocks or the OD is just slightly oval.

 

[wood2steel]

Let the Premium barrel manufacturers worry about the barrel cocentricity. There are so many other variables out there that will make or break a good barrel once its in place. 35 yrs ago, Cryo Technology, floating barrels, glass bedded barrels and actions were the norm. Cannot imagine what new Technology exists out there today. Barrel stress and ammo selections are how we dialed in a most rifles to be consistent sub MOA shooters

 

[MilGunsmith]

What happens in the bore is more important than outer dimensions. You cant check for bore straightness by measuring the outside. If you go to one of the Benchrest Forums, you will see this discussed a lot. When setting up to chamber or crown, all measurements and indicating is done off the bore, the outer diameter is ignored. Good chambering and a good crown are what is important. Bent barrels have been known to shoot exceptionally well.

 

[neanderthal mach]

In general, the accepted and usual advise about barrels is to index any known bore run out so it's maximum tir is pointing either straight up or down at the muzzle end. For ultra long range shooting it's always up for obvious reasons. Whatever your trying to check using that method is about meaningless since you really don't know if the barrel O.D. is in fact concentric to the most important part, the bore. And I'd almost bet money it isn't. A Barrel could be straightened, but if you have to ask how to do it, then its way beyond what you should even be trying. That's what highly experienced pros are for. Buy from a known barrel maker, get it chamber, threaded and installed by a pro and forget about it after would be my advise.

Secondly, very few even knowledgeable shooters and reloaders have ever bothered to find out using proper facts and logic exactly why as they all like to say, a rifle "likes" this load or bullet combination, and might refuse to shoot well with any other combination. A rifle barrel is just about the same as a proper tuning fork, and even macro level vibrations from just the triggers components starting to move and before the sear even breaks, that barrel tip is moving more than enough to matter. Vibrations travel at upwards of 13,000 mph in steel depending on the exact physical characteristics that particular piece of steel happens to have.

As the sear breaks and the firing pin starts to move, those vibrations start to increase, the firing pin slamming into the primer increases them even more. All this is happening at low millisecond levels. Initial powder ignition and bullet movement down the bore then starts a literal low sine wave shape to the barrel that can be clearly seen with very high speed photography. Whatever load combination that rifle "likes" the best, is simply due to the particular vibration harmonics that barrel has and will replicate to very close limits during every shot. Calculate just how small a 1 moa or 1/60th of a degree really is. (1.0472" difference in 100 yrds) And you'll then understand just how important obtaining that exact same vibration frequency and barrel sine wave effect is. A .001" difference in muzzle position as the bullet exits the barrel between each shot vastly increases your group size. If you really want better accuracy, then start learning what effects will or will not produce it first.

And if your not already doing so and you do reload? Proper flash hole internal deburring, hole resizing, as well as re-cutting the primer pockets with the proper tool to a known size and flat pocket dimension will also help with shot to shot consistency. Then ignore about 90% of the total bull shit that's promoted on Youtube and the reloading forums as facts unless there from trained factory internal and external ballistics experts that do actually know what there doing.

 

[Toolmaker51]

In the 1950's I read a book on one of the early 19th century American long gun makers. I recall that the barrel straighteners sighted through the bore on a wire stretched tightly across a window in the shop to detect bends in the barrels. That was long before dial indicators were available and is a reminder that there are often simple-seeming solutions to problems that were developed by practical mechanics working with what was available to them. Often, old ideas that worked before will still work.

Larry

......a north window IIRC. Suspending a weight (vertically) is much easier. We examine telescopic square tubing for kinks this way.
V-blocks and indicator render only cosmetic results. Indicators have been around quite some time, the earliest were simple levers, not clockworks. What is newer, the increasingly finer increments.

 

[Road_Clam]

Ive seen a great many barrels ,new and used ,that had runouts of the external form of as much as .012"TIR...........the simple way of checking the internal bore for straightness is with short rods ground to slightly under bore dia , maybe 1/2 thou under ......one rod will be 1/2" long ,the other 6" long .....the first rod checks for bore diameter regularity ,the second rod checks for straightness.......both rods should be a light,even push thru the bore..........From before WW2 ,the arms factories had electronic bore straightness gauges for finish rifled barrels............No doubt most here have heard of the famous "Star Gauge " used by Springfield Arsenal for checking bores .

Heres an interesting vintage vid of the original Springfield Armory facility at about 3:00 you will see a very interesting barrel straightening fixture. I have no idea as to how it works but im guessing some type of refractive lighting to identify internal bore flaws ?

 

[john.k]

The reflection method of straightening is very well known,however it doesnt work with a rifled bore ,as the reflections are then very difficult to interpret ........consequently barrels are straightened before rifling.........after rifling,the close fitting rod,or an eletrical method are used to check straightness. .........I dont believe any premium maker straightens rifled tubes any more............they simply sell the rejects as seconds,gunsmith specials,unbranded bulk barrels etc.

 

[cyanidekid]

barrel straighteners were considered some of the most, if not the most, important of the skilled tradesmen in the arms factories of WW1 (and later as well). if you search, you'll find video of these guys sighting down the bore, rotating them, and spinning a hand wheel that bends the barrel truer. even given the mismatch of frame rate (what makes most old film look like everyone was on speed), they still seem to take about 10-15 seconds per barrel to straighten each one. I don't know what purpose these barrels were intended for, wether they were "sniper" or "general issue", but its clear that sighting down the bore was how they were trued.

 

[john.k]

During WW2 ,most governments determined that provided the muzzle 6" of a bore was straight ,the rifle would shoot to requirements..............the local deep drilling shop has state of the art machines and claims straightness and finish that make honing or finish reaming unncessary..........incidentally,the worst production barrels ive ever seen (this includes Chinese WW2) is the NEF break action guns.........the rifling is mainly gouges from trapped chips and broken cutters........they shoot acceptably.