AR10 gunsmith questions.

[Jack506]

Just to be clear on your problem:

You fire, the empty case stays in the chamber, the bolt picks up a live round from the magazine, and attempts to feed it into the back of the empty case?

Usually it is the last round that fails to extract, bolt locks back but the round is still in the chamber. Sometimes hand cycling works, sometimes it take several tries for it to strip the casing out of the chamber.

I'm curious OP. What brand upper and bcg are you using?

Barrel also?

The upper is a Gibbz side charging, bcg is an unmarked dpms pattern, has a 18” Faxon pencil barrel with the superlative arms bleed off gas system.

 

[cmshoot]

What is primary cause of this type of function?

My first guess would be a weak extractor spring, or out of spec extractor.

-Weak spring allowing the extractor to slip off.

-Out of spec extractor groove that is either too shallow, or not "square" enough to keep a good purchase on the cartridge rim.

It's weird that it's usually the last round that does it. Can't figure out what difference that would make, for this type of malfunction.

Opening the gas port will not change your issue, and may cause other issues. If your bolt is locking back consistently after firing the last round, then you are getting enough gas to do what needs to be done.

It's possible that you could have an out of spec chamber/too tight/rough chamber that is causing the failure to extract.

What ammo are you having this issue with? Have you tried more than one type of ammo in it? Issue could be the ammo.

Depending on what your answers to the ammo questions are, my recommendation is to look at the extractor/extractor spring first. Install new extractor springs. That doesn't work, replace the extractor.

Start with the cheapest/easiest fix first and work your way up from there.

 

[Jack506]

The ammo has been a mix, old surplus, ppu soft points, even some milspec-ish reloades.

My first guess would be a weak extractor spring, or out of spec extractor.

-Weak spring allowing the extractor to slip off.

-Out of spec extractor groove that is either too shallow, or not "square" enough to keep a good purchase on the cartridge rim.

It's weird that it's usually the last round that does it. Can't figure out what difference that would make, for this type of malfunction.

Opening the gas port will not change your issue, and may cause other issues. If your bolt is locking back consistently after firing the last round, then you are getting enough gas to do what needs to be done.

It's possible that you could have an out of spec chamber/too tight/rough chamber that is causing the failure to extract.

What ammo are you having this issue with? Have you tried more than one type of ammo in it? Issue could be the ammo.

Depending on what your answers to the ammo questions are, my recommendation is to look at the extractor/extractor spring first. Install new extractor springs. That doesn't work, replace the extractor.

Start with the cheapest/easiest fix first and work your way up from there.

 

[Allsmiles]

Not me, buddy with 243 AR10 that he yote hunts with.

 

[Dirty J]

Sounds like an old PSA 308 barrel I had where they apparently machined the chamber with a brick…

 

[Jack506]

Sounds like an old PSA 308 barrel I had where they apparently machined the chamber with a brick…

It’s a Faxon, so in would expect that to be the problem.

 

[Dirty J]

It’s a Faxon, so in would expect that to be the problem.

Good luck with it. cmshoot is pretty much all over the troubleshooting progression… less expensive to most.

1) test fit some different ammo just to rule that out
2) extractor tension/geometry
3) barrel/chamber

One (or more) of those will get it sorted.

 

[Jack506]

Thanks for everyone’s input! Replacing the extractor fixed the issue.
On another note, anyone have an idea what would cause it to over run the round on only half the magazine? My ASC mag works fine. It the Magpul jams every other round.

 

[Dirty J]

Thanks for everyone’s input! Replacing the extractor fixed the issue.
On another note, anyone have an idea what would cause it to over run the round on only half the magazine? My ASC mag works fine. It the Magpul jams every other round.

You’re saying it jams for 1/2 the mag (top or bottom)? Or when it’s always feeding from the left or right side of the mag?

If the latter… probably an issue with the feedramp.

 

[Jack506]

You’re saying it jams for 1/2 the mag (top or bottom)? Or when it’s always feeding from the left or right side of the mag?

If the latter… probably an issue with the feedramp.

It’s the latter, however it jams by the bolt over riding the rounds thus partially feeding before crush’s the side of the round. Happens while charging or firing.