Overgassing?

[The Heretic]

So, as stated above, stick with ammo that your rifle likes.
Sell off the F&S ammo.

Or get another rifle that likes the ammo.

There is also benefit in having a self-defense rifle that works with as much ammo as possible. If SHTF you may not have the ability to pick and choose ammo.

 

[11Charlie]

That certainly can be a bit obnoxious Shooting next to a suppressed gun is much more fun! As is shooting a suppressed gun!

Sounds to me like you need a can!

 

[DirectDrive]

So what dose the chamber look like?
Is it smooth and well shaped. Or are there obvious machine marks or some other flaw.

It seams strange to be both over gassed and not extracting?

It was working with other ammo.
With hotter ammo, it's conceivable that the extraction process is starting too soon and before the fired case contracts slightly.
I think this was mentioned above somewhere as well.

 

[The Heretic]

So what dose the chamber look like?
Is it smooth and well shaped. Or are there obvious machine marks or some other flaw.

It seams strange to be both over gassed and not extracting?

If the gas is too much and/or too soon, the timing can be off, causing the bolt to move to the rear before the case has had time to shrink while there is still pressure holding it against the chamber walls, causing the extractor to chew up the rim and ride up over it, causing a failure to extract.

A stronger buffer/recoil spring, i.e., increased resistance to the bolt moving rearwards initially, can help.

 

[HB of CJ]

I do not know anything about the AR10. First thing that would be universal is to check the head space. If correct then contact the barrel maker. Possibly the gas port diameter is not correct. Also possible you have some specification or precision error with the bolt head and extractor.

You are plowing fresh ground with your AR10. Not a factory variant. Over gassing is a specification and precision problem: it is NOT a situation quickly or easily addressed by changing out other stuff like the buffer or spring. Not going to help. An adjustable gas block may or may not help either.

If you decide to go to an adjustable gas block get a high quality STEEL clamp on version using at least 2 and preferably 3 high grade Allen screws. A taper pin version would be best but probably non doable in your situation. Crank down the gas until the gun cycles reliably but not force ably Good luck.

Linux Spell Check Is A Hoot.

 

[etrain16]

Sounds to me like you need a can!

a can? No, I need several cans!

 

[Greenbug]

The primer is flattened out indicating a pretty hot load. Probably that ammo is the problem especially since you mentioned that it shoots other ammo just fine. Ditch the F&S ammo or shoot it in a different gun.

 

[Grimm]

All the clues are in post #1

1) You reported that the rifle works fine with "other" ammo
2) That indicates that you have an AR308 compatible buttstock system
3) It's your ammo

It is general consensus that civilian 308 ammo is loaded hotter than military 7.62x51
This is another topic with lots of disagreement, but there are differences in the 2 types of ammo.
(and in the chambers)

So, as stated above, stick with ammo that your rifle likes.
Sell off the F&S ammo.

I need to go shoot it again with different ammo and double check that it actually looks fine with it. The last few times I've shot I haven't paid much attention. I know its maiden voyage though it was fine.

So what dose the chamber look like?
Is it smooth and well shaped. Or are there obvious machine marks or some other flaw.

It seams strange to be both over gassed and not extracting?

I'll take a look at the chamber. It seems to me, Heretic has it right based on it symptoms. It's trying to rip the casing out before it has the opportunity to fully contract and that friction is what gave me the FTE/bent brass.

If the gas is too much and/or too soon, the timing can be off, causing the bolt to move to the rear before the case has had time to shrink while there is still pressure holding it against the chamber walls, causing the extractor to chew up the rim and ride up over it, causing a failure to extract.

A stronger buffer/recoil spring, i.e., increased resistance to the bolt moving rearwards initially, can help.

I'm leaning in this direction. I'm going to try to head out somewhere maybe today and put some Federal through it. Ill report back with what it looks like. Even if the different ammo looks okay, I still may consider going with a heavier buffer. I'd like to be able to shoot anything that says .308 on it...

Could the fact that my nibo bcg is "slicker" have anything to do with it moving any faster?

 

[Medic!]

It was working with other ammo.
With hotter ammo, it's conceivable that the extraction process is starting too soon and before the fired case contracts slightly.
I think this was mentioned above somewhere as well.

If the gas is too much and/or too soon, the timing can be off, causing the bolt to move to the rear before the case has had time to shrink while there is still pressure holding it against the chamber walls, causing the extractor to chew up the rim and ride up over it, causing a failure to extract.

A stronger buffer/recoil spring, i.e., increased resistance to the bolt moving rearwards initially, can help.

I know.
Some brass is soft. Some harder. And steel case ammo is least likely to grasp a rough chamber.



Guys it's not rocket science. Just look at the chamber and find out.

 

[Grimm]

I know.
Some brass is soft. Some harder. And steel case ammo is least likely to grasp a rough chamber.



Guys it's not rocket science. Just look at the chamber and find out.

Like I said, I'm new. I should look down in there at the chamber/inside of the barrel and see how smooth or not it is?

 

[Grimm]

Thanks for your help guys. I'll screw with it and report back. I know you're all at the edge of your seats!

 

[DirectDrive]

Guys it's not rocket science. Just look at the chamber and find out.

A worn reamer will produce a rough chamber, BUT it was working with other ammo so I wouldn't suspect a rough chamber to be the cause. The change in extraction/ejection happened with the F&S ammo.
A headspace check is good advice.

 

[Medic!]

A worn reamer will produce a rough chamber, BUT it was working with other ammo so I wouldn't suspect a rough chamber to be the cause. The change in extraction/ejection happened with the F&S ammo.
A headspace check is good advice.

Heavy projectile creating more back pressure? Softer brass in one load?
These and other things can bring the finish of the chamber more into play.

So you wouldn't suspect a rough chamber?

Why? It takes nothing more than a light, your eyes, and one minute to find out.

 

[Tomahawk67]

A quality adjustable gas block will make this right. Most .308 ar barrels are severely overgassed from the factory.
Adding a suppressor to the rifle will increase internal gas pressure even more which is why dedicated suppressor barrels have smaller gas port sizing, and people that run a dual role(can & no can) usually also run an adjustable gas block.

 

[Grimm]

Checked the chamber. Very dirty and dry but looked well machined/smooth.. Ran a snake through it and some oil. I might head out the wolf creek road with the wife in a bit and give it a go.

I'm probably going to get a adjustable block at some point just to have it. I almost got one starting the build but I sent the money in another direction instead. At least if I get one, it'll be one step closer to my can

 

[DirectDrive]

Checked the chamber. Very dirty and dry but looked well machined/smooth.. Ran a snake through it and some oil. I might head out the wolf creek road with the wife in a bit and give it a go.

I'm probably going to get a adjustable block at some point just to have it. I almost got one starting the build but I sent the money in another direction instead. At least if I get one, it'll be one step closer to my can

You're doing the right thing sticking to 308 Winchester ammo according to Faxon's statement below :

7.62x51 NATO is not the same round as .308 Winchester, though it will fit within chamber. 7.62x51 technically requires deeper headspacing to meet the military specification and is known to function in Faxon .308 WIN barrels under most circumstances. However, due to the variation of components in the .308 AR world and variations between loadings, Faxon cannot guarantee or warrant function with 7.62x51, especially with bolts with tight ("match") .308 WIN headspacing.

When/if shopping an adjustable GB, make sure it will fit under/inside your handguard.
Often they will be taller than a conventional GB.

Good luck

 

[The Heretic]

You're doing the right thing sticking to 308 Winchester ammo according to Faxon's statement below :

7.62x51 NATO is not the same round as .308 Winchester, though it will fit within chamber. 7.62x51 technically requires deeper headspacing to meet the military specification and is known to function in Faxon .308 WIN barrels under most circumstances. However, due to the variation of components in the .308 AR world and variations between loadings, Faxon cannot guarantee or warrant function with 7.62x51, especially with bolts with tight ("match") .308 WIN headspacing.

This issue has been going around for decades for both 5.56x45 and 7.62x51.

I have yet to encounter/shoot a rifle that had safety problems with either NATO or SAAMI or CIP spec ammo, regardless of whether it was chambered for 5.56 or .223 or 7.62 or .308

I think most of the warnings the manufacturers give are CYA statements for liability.

 

[campwilde]

First off, the 3 o'clock position is the correct spot for brass to land. Under gassed is 4 and 5 when the bolt comes back slower and late letting the ejector and ejection pin/spring to fling it to the rear. Over gassed is 12,1 & 2 as the casing comes out to hard and will bounce off the rear of the upper ejection port bouncing it forward. A suppressor will make an over gassed situation even worse as it holds pressure in the barrel longer with that pressure going all the way to the BCG making gassed higher than without the suppressor on the end of your barrel. Yes the guy that said you can use a Adj. gas block to fine tune it but you will probably have to make changes when removing the suppressor or it will be under gassed. I did put a flat wire buffer spring in my CA-10 and it holds close to the 3 o'clock position whether the suppressor is on or off. It seems pretty smooth as well. It is a pretty high end Ar but the spring seems to have enhanced it quite a bit. Just my experience.

 

[campwilde]

An Ar10 should function like a kicking mule if you put an ar15 spring in it. An ar15 buffer is a whole different ballgame and is iffy at best. A 5.56 cartridge is more powerful than the .223 and the 308 is more powerful than the 7.62. In both instances it is small but different.

 

[campwilde]

The 3 o'clock position is the correct landing spot for brass. Under gassed is 4, 5 and 6 when the BCG is moving rearward slower and late letting the ejector along with the ejector pin/spring to fling it to the rear and sometime not picking up the next round, and not locking open on the last round. Over gassed is 12, 1 and 2 o'clock positions when the BCG is moving back to hard and fast causing the casing to hit the rear of the ejection port and bouncing forward. A suppressor will take an overpassed situation and make it worse because it holds the pressure in the barrel longer all the way back to the BCG. The person who said an ADJ. gas block is correct (Many other options too). The drawback sometimes with the adj. block is you many times have to change the adjustment when switching between suppressed and non-suppressed firing. I solved mine by going with a flat wire buffer spring and get a 3 position on my CA-10 with and without the suppressor. The spring also had a side effect on mine of a much smoother shooting gun. It is all about bolt timing. by the way, a 5.56 is more powerful than a .223 and a 308 is more powerful than the 7.62 fo your info.