Case mouth denting in gas gun

[Ron Blain]

Not really unless you start shooting under powered ammo which may result in short strokeing.. Almost every AR with a short gas system will benefit from tuning.... Knowing if the gun is overgassed or under would be a start..

Most of them are over gassed to shoot cheap crap ammo which is under powered.. You don't really run into over powered ammo but you do under.. Especially in .223 carbine length gas systems they are normally over gassed and beat themselves up..

Most manufacturers are not going to add an h1 or h2 buffer becouse of cost not to mention it would defeat their idea of running an enlarged gas port for reliability.. Along those lines they are not going to add an increased power recoil spring either.. In the m4 platform I run a heavy buffer and stock power spring.. Good companies run an h-buffer but I believe colt has started shipping with an h1 now which increases lock time and well buffers better..

If you want to shoot cheap ammo and it short strokes simply use the stock buffer and spring, it doesn't get any easier to change back but I don't know why you would.. Good ammo is always better than cheap ammo.. There's a reason federal GMM and black hills cost more than tula... Also yes those cases will reload no problem , just run them through the die..

I agree with that. Problem is I have seen people try and tweak a rifle to eliminate bent or dented cases on ejection only to later change ammunition and the issue returns. Looking at the above case mouths and the fact the original poster mentioned they were shooting sub MOA I would not worry about it, especially in .308 Winchester. That said, I absolutely agree with what you are saying, especially with under or over gassing. What I really strongly with is never get me started on cheap ammunition and yes, there is a reason the Federal GMM and Black Hills Match cost more and short of rolling one's own they perform well.

I guess the original poster could try a few other flavors of ammunition and see how it behaves and if the case mouths remain dinged.

Ron

 

[Rsadams]

I agree with that. Problem is I have seen people try and tweak a rifle to eliminate bent or dented cases on ejection only to later change ammunition and the issue returns. Looking at the above case mouths and the fact the original poster mentioned they were shooting sub MOA I would not worry about it, especially in .308 Winchester. That said, I absolutely agree with what you are saying, especially with under or over gassing. What I really strongly with is never get me started on cheap ammunition and yes, there is a reason the Federal GMM and Black Hills Match cost more and short of rolling one's own they perform well.

I guess the original poster could try a few other flavors of ammunition and see how it behaves and if the case mouths remain dinged.

Ron

Exactly , right now you can't really say what's wrong, actually nothing is wrong with the gun. There's to many variables at play. Is the gun brand new? How many rounds through it? I won't make a change until at least 200 rounds are through it , full power rounds. To me its not broke in till then and that may not be enough... The word milspec gets thrown around to much these days and has lost its meaning really.. Milspec does not mean best it means milspec and lets not forget that means normally cheapest bidder.

My knowledge is in the m4 platform not the sr25 I have not spent that much time behind the .308 version.. I would not think of changing anything till I knew the port size and what it should be.. And you don't have to change anything , the rifles working fine..

As you said maybe just try some different ammo. With the m4 you see this becouse companies know people are going to cheap out on ammo and they get tired of getting calls on why it won't cycle tula .223 plus they don't care if there's more wear.. They just say it's normal.. As people have stated this platform is real hard on brass and those cases are not that bad.. Altho there's ways to stop it , if you call the manufacturer and send them those pictures they will say its normal and not to worry about it..

 

[Richard Coody]

We all know ARs beat up brass. A pad on the shell deflector helps. They also mess up rims.

One thing about the picture of the cases has me curious. Can someone enlighten me as to why there is carbon all the way down past the shoulder on that brass.

 

[SheepDog]

You should be able to tune the ejector to stop the denting of cases. Carefully stone the ejector to shorten it slightly and radius back on the face of it to the outside. This moves the ejection later and puts less rotation on it. I've done this on 1911s and AR15s.

 

[Knotwild]

What length gas system does your rifle have? I see that Live Free Armory sells both mid length and rifle length in .308. The mid length is going to be harder on brass than the rifle length. I suggest putting an SLR adjustable gas block on it and tuning it for your load. It has detentes to make it repeatable when changed and it adjusts from the front with a long Allen wrench so you don't have to remove the hand guard to adjust it. I like it better than changing buffers and springs because it can be tuned to any load you use quickly.

 

[Bart B.]

Has anyone tried cutting a turn or two off the ejector spring?

I ask because that's how I've "tuned" Garand case ejection directions. Once fired cases go out at 1 o'clock there are no more dinged cases nor hot cases bouncing off your forehead.

 

[Liven The Dream]

I read enough jokes on this one ..
There is no reason this can not be repaired..
The glue on rubber on the upper is good.
Did for some or my AR's
The gas hole in the Barrel Size is important.
The ejector spring can be cut , remove a coil or two.
Caution: This works will if your shooting the same Ammunition. if you shoot a box of this then two of that will ????
The PSI will differ and the Rifle will function different .
Don't sell it they are great

 

[T-shooter]

Like Don said, as long as the gas system is working with a certain ammo, it will be fine once adjusted. But if you change ammo, the ejection path will also change. Slower ammo doesn't touch on my AR15 but hot loads used to hit the deflector hard enough to partially crush the shoulders. A cheap simple fix (with things I already had) was a piece of an old black mouse pad about 1/8" thick and glued it on with black silicone. Once it dried I could do any final trimming with a razor blade. Since I did this fix, I've never dented another case and the piece if pad has never come off.

 

[Ggmac]

Yup ! I bet that there's an indent in the primer , somewhere in the center ? What's that all about , is my gun OK ? Should it be on all the primers ?
Dang it's all so confusing !
Sorry I'm just having some fun . Oh shoot , the bullet is missing also , is that normal ?
I noticed that the bullet is missing ONLY on the cases with the indented primer , is that a coincidence ?

 

[Rsadams]

I am sorry glueing a piece of rubber on the shell deflector is not really getting to the root of the problem... But to each their own..There's no reason to let an over gassed gun beat itself to death over $100, if that much..And no don't sell it , its not that bad I have seen alot worse..

 

[hogan]

Has anyone tried cutting a turn or two off the ejector spring?

I ask because that's how I've "tuned" Garand case ejection directions. Once fired cases go out at 1 o'clock there are no more dinged cases nor hot cases bouncing off your forehead.

This +100.... Don't want your ejected brass flying all over the place anyway. Buy a few extra ejector springs and experiment. I like to be able to press the ejector in with thumb or forefinger. If your rifle is grouping well and you want to seek further improvement, keeping the case fully engaged with the boltface is important. Also important with bolt rifles.

 

[Bart B.]

If your rifle is grouping well and you want to seek further improvement, keeping the case fully engaged with the boltface is important. Also important with bolt rifles.

What keeps the case head against bolt faces?

I'm not aware of any mechanics in rifles that does that. Extractors don't do that. Excluding cases whose various dimensions are greater than those of the chamber; they'll make case heads press against bolt faces; a well known cause of accuracy problems. The bolt binds a little when this happens.

 

[DirtySteve]

Some one has already said it but the solution is an adjustable gas block. I have one on all my gas guns. It made my wives gun shoot much better groups. Cutting coils and heavier buffers may help but the gas block fixes it for good.

 

[Richard Coody]

Some one has already said it but the solution is an adjustable gas block. I have one on all my gas guns. It made my wives gun shoot much better groups. Cutting coils and heavier buffers may help but the gas block fixes it for good.

Until it stops up from carbon.

 

[DirtySteve]

Haven't had it happen, yet...

 

[JarheadAZ]

As long as the rifle is shooting well, as you suggest, I don't think there's any really good reason to mess with the rifle's features. The Velcro trick should reduce/eliminate the problem without affecting accuracy in any substantial way.

I F/L resize with the sizer ball, and this produces loadable brass. Dents in the shoulder should blow out early in the firing cycle before peak pressure is attained, and I doubt the bullet and barrel will even notice they are there.

Yes, there are a bunch of more advanced steps to take; but I probably wouldn't bother. Semis and dented brass are a common, minor problem.

Greg

 

[hogan]

What keeps the case head against bolt faces?

I'm not aware of any mechanics in rifles that does that. Extractors don't do that. Excluding cases whose various dimensions are greater than those of the chamber; they'll make case heads press against bolt faces; a well known cause of accuracy problems. The bolt binds a little when this happens.

A minimal spring rate on the ejector assures full contact with boltface. Mostly applicable to a boltrifle with minimum oal chamber, but if you have a bolt with uniformed face, the higher spring rate on the ejector tends to cant the case. An autoloader needs .002-.003" minimum headspace to negate slamfire potential, and more is probably better.

 

[Bart B.]

What mechanics pull chambered round case heads back against bolt faces?

if you have a bolt with uniformed face, the higher spring rate on the ejector tends to cant the case.

How can that happen? Never heard of such chambered cartridge manipulation. If that's true, wouldn't the firing pin striking the primer with 25 pounds of force do that with a Mauser style ejector that's still under the bolt when the round fires?

I've never seen any rifle whose chamber and cases are within specs allow rimless bottleneck case rims stop against extractor lips from ejector or firing pin driving them forward. They all stop when their shoulder is hard centered in the chamber shoulder. A few thousandths inch or more clearance from case rim to extractor lip is normal and mandatory. Such ammo fires when full forward in the chamber with a little clearance from case head to the bolt face.

That clearance allows for easy chambering the round and allows the chamber shoulder to hold the case still from firing pin impact, not the extractor. The end result better centers bullets in the bore.

All rifles need one to a few thousandths minimum "head clearance" from bolt face to case head. Several thousandths head clearance average is normal with M1 and M14 service rifles shooting arsenal ammo. Almost that much with commercial ones. There is no commercial or military spec for head clearance; it's the difference between case headspace and chamber headspace, whatever each may be.

That clearance means nothing for firing pin tips that usually stick out at least .060" past the bolt face and most primers need dents at least .020" deep to fire.

The force firing pins put on bottleneck cartridges is enough to set case shoulders back .001" or more before the round fires. I've measured 308 Win case shoulder setback from .002" to .007" depending on spring force and case type. Measured empty primed case headspace before and after firing them. New Federal nickel plated cases with 15% reduced loads with 168's ended up with about .007" less case headspace; primers backed out .008" or so from case heads.