Effect of USGI bolt on accuracy?

[Joel]

I've got a question I figured the collective here could help me with.

Picked up an old import M14 and it headspaces quite long (I know, shocker right?) With a 1.636" gauge in the barrel and the bolt closed on it, I can slip a 9 thou feeler gauge behind the bolt lug between it and the receiver, and its just enough to say I can't with a 10 thou gauge, so I am calling it approx 1.645" hillbilly headspace check.

Its averaging around 4" groups with both some Hornady and Fed. blue box ammo. Some a bit smaller, some a bit bigger. I feel like it should be doing better.

Now I can tell it has a bit of room to move in its Chu wood stock both side to side and slightly front to back in its stock liner as well. No es bueno, I know. Not like SKS bad but still, its enough to say it can move. And the gas cylinder lock can rotate past index.

What I want to know is, how much does lapping in a USGI bolt affect consistency of shooting? I know it helps brass life, etc to have the shorter headspace, but does it come with any accuracy gains? How does that compare to, say, a properly fitting stock and tight gas system?

 

[Alpheus]

Won't lapping the lugs increase the headspace?

 

[Joel]

When you add a USGI bolt to a Chinese receiver, your headspace has a good chance of being smaller than "Go" dimensions.(In fact, it may not even be able to close) So you really do have to lap them in, and it still results in much smaller headspace than with your Chinese bolt.

So yes it does increase headspace, but like the old Yiddish fellow with the crazy hair said, it's all relative. I could very well end up going from 1.645" to 1.632" or thereabouts.

 

[just having some fun]

You can also reload brass (shoulder not neck) on the long side..

as long as you keep ammo separate for the one rifle as it might jam on a different rifle

 

[Joel]

I only have the one 308 (for now...addict that most of us are) so thats kinda what I am planning. Screw in the die to bump the shoulder back enough for it to chamber easily, but thats about it.

Thinking the better stock and tighter gas system are easier, cheaper solutions. But if its always gonna shoot like a dog, might as well swap the bolt too.

Not lookin for a match rifle here. Would be happy with a consistent sub 3" performer. Say repeatable 2.5"

 

[Claven2]

Changing bolts, by itself, won't do much unless the lugs on your chinese bolt are not bearing evenly.

Foremost, I would either bed your stock or get a better one. Then shim your gas system and see what that does before shelling out for an expensive replacement bolt.

 

[Joel]

Thanks Claven2, I appreciate the feedback.

Think I'll try finding a tighter stock, or bedding if I can't. And looking for a different gas cylinder lock, if possible.

 

[Claven2]

Try flipping the lock around. But cheaper than a new lock would be some shims. Most guys just use the shims.

 

[Joel]

Will do!

I have a few of the shims, from Brownells. How long do they last?

Looks like the flash suppressor has already been removed on this rifle too, should help

 

[cr5]

Once you bed the stock and shim the gas system I'd try some different ammo before investing in a new bolt.
Sometimes you just need to figure out what ammo the barrel likes, could end up being same weight just a different brand that hits the right harmonic.
What are you using for optics and mount? If you're shooting with the irons you may not get much tighter groups unless you're pretty good with them. What I'm doing with my cheaper more original M305 is using a scope during load testing then once I find a good load for it I plan to go back to irons.
Good luck

 

[Claven2]

Will do!

I have a few of the shims, from Brownells. How long do they last?

Looks like the flash suppressor has already been removed on this rifle too, should help

They are steel and should last forever. Its just to get the gas lock timed by taking up space to the barrel shoulder.

 

[1-trident-1]

bullet, barrel, bedding for accuracy. ditch the chui wood, get a fiberglass stock. I have worn out a shim, but that's ok, it's the cheapest part. at 45 you are at the max. not good. bolt must be stripped to measure head space.

 

[Claven2]

bullet, barrel, bedding for accuracy. ditch the chui wood, get a fiberglass stock. I have worn out a shim, but that's ok, it's the cheapest part. at 45 you are at the max. not good. bolt must be stripped to measure head space.

You wore out a shim? You realize you are not supposed to touch the gas lock for normal cleaning, right?

 

[1-trident-1]

You wore out a shim? You realize you are not supposed to touch the gas lock for normal cleaning, right?

the shim takes a pounding, it is not a permanent solution, proper gas lock, unitized band and cylinder is. you do have to shoot a few thousand rounds to do it. once bedded, disassembly is kept to a minimum. no need to undo the gas lock to clean the cylinder and plug.

 

[Pr589]

You wore out a shim? You realize you are not supposed to touch the gas lock for normal cleaning, right?

I also have worn out a shim. It took 800+ rounds to do it but all that was left was dust and a sliver of the old shim. Found the issue after groups started to open up.

 

[Joel]

That is why I was asking, not the first time I've heard of the shims ending up loosening or compressing over time, but at least it is cheaper than welding the gas system! The bolt was stripped when I measured headspace. Interestingly, putting in a different Chinese bolt brought it to below 1.630! Would have to lap it in. But I am selling the rifle that bolt came with, so...

CR5, thanks for the suggestion on the ammo. I plan to! The problem is not the loose nut behind the butt...this time

Today I'll try it in a Chinese synthetic stock that it fits tightly, and with the shims.

 

[Claven2]

That is why I was asking, not the first time I've heard of the shims ending up loosening or compressing over time, but at least it is cheaper than welding the gas system! The bolt was stripped when I measured headspace. Interestingly, putting in a different Chinese bolt brought it to below 1.630! Would have to lap it in. But I am selling the rifle that bolt came with, so...

CR5, thanks for the suggestion on the ammo. I plan to! The problem is not the loose nut behind the butt...this time

Today I'll try it in a Chinese synthetic stock that it fits tightly, and with the shims.

No two chinese bolts are alike. So that's not unusual.

 

[Claven2]

the shim takes a pounding, it is not a permanent solution, proper gas lock, unitized band and cylinder is. you do have to shoot a few thousand rounds to do it. once bedded, disassembly is kept to a minimum. no need to undo the gas lock to clean the cylinder and plug.

To be honest, I use unitized gas systems and no shims in my own guns, but never had a shimmed gun come back to me after someone requested a shim install. Interesting.

Fwiw, I have generally found the most important thing to clean is the inside of the piston. Cylinders are somewhat self-cleaning and the plug is less critical.

I cleaned a used IDF piston last week that was literally plugged from the tip to the port and the diameter forward if the port was reduced by half. Near as I can tell the gun must have seen lots of full auto and nobody ever bothered to clean the gas system. It should not have been running well when it was scrapped and sold to wolverine.

Some of the IDF guns were clearly run very hard and were essentially worn out when surplused. Others weren't too bad.

 

[Joel]

Yikes, sounds like that one has had some hot suppers.

I'd picked up from Gus Fisher a few years back that just swapping pistons can significantly effect accuracy, likely on account of dwell time.

 

[1-trident-1]

the Pandora's Box of pistons. U.S. armorers tried by experimentation, measuring to see why a rifle preffered a certain piston. after all the measuring and trials, they couldn't find a relationship. new , used or beat up, had little bearing. My guess is harmonics. After your smith has accurized your rifle, buy a handful of pistons, and try each one, keep the best, sell the rest. my best turned out to be a used old GI piston. TiN coated didn't work for me, it has for others. chicom pistons for chicom cylinders, USGI, for USGI. don't mix, the bores are different. do this after accurizing, not a cure to shrink groups, just a refinement. enjoy the journey, the destination isn't guaranteed.