Please help. My AR10 is short stroking.

[fatelvis]

I just bought an AR10 lower and 20" M5 upper in 6.5 Creedmore, both from Aero. It has a rifle length gas system. I assembled 20 rounds from components I had on hand, and the rifle will fire, eject the brass at 3:00 smartly, but will not go back far enough to strip off the next round, or lock back the bolt on an empty mag. The ammo I loaded was Starline virgin LPP brass, 41 grains RL15.5 under a Hornady 123 match bullet to 2.71" OAL. What would be your first course of action in correcting this problem? Thanks!

 

[Bill Norris]

Do you have an adjustable gas block ?

 

[fatelvis]

Do you have an adjustable gas block ?

No, just the standard OEM gas block from Aero.

 

[Bill Norris]

No, just the standard OEM gas block from Aero.

Sounds like it may need more gas but there could be something else lurking somewhere. Have you check for a burr anywhere in the bolt mechanism ?

 

[Dave M.]

Wrong buffer spring???

 

[SKWERLZ]

Possibly easy fix is a lighter buffer.
What sping and buffer now?
You can check bolt head and carriers dimensions.
Pinned gas block?

 

[Mark M.]

Check your gas block alignment

 

[Twdmar]

Is the gas key tight? Is there evidence of carbon blowing out around the gas block? Are you using a powder that doesn't provide enough gas pressure?

 

[fatelvis]

I’m going to check the gas block for evidence of a leak. How do you check alignment?

 

[fatelvis]

The buffer and spring are what came stock from Aero

 

[Lone Hunter]

My money is on the gas block misaligned. That is what was always my problem. But, I have lost money before too…

 

[jelenko]

My first course of action would be to ask the seller. Although, they will probably want you to try some factory ammo.

New AR10 should just cycle - period.

 

[fatelvis]

I am going to waste my money and try one box of factory ammo, just to use it as a baseline

 

[shoobe01]

I’m going to check the gas block for evidence of a leak. How do you check alignment?

Best today is a borescope. Just look. Otherwise... I dunno without removing and doing every every step as carefully as possible to assure it's correct.

One note as you start looking for every minor flaw, is that — unlike at the gas key — at the gas block minor blowby is NBD. Alignment matters but there's no gasket etc because it doesn't matter up there.

 

[shoobe01]

I am going to waste my money and try one box of factory ammo, just to use it as a baseline

This is also an important diagnostic. The most boring M80 mil ball similar stuff you can get, to be sure the gun is working at baseline or not.

 

[SKWERLZ]

My money is on the gas block misaligned. That is what was always my problem. But, I have lost money before too…

Pretty common problem
Many gas blocks are dimensioned to be spaced with a handgaurd sheet metal mount and if gas block is back tight to journal face without handgaurd mount they go back too far.

Some newer gas blocks have a bigger hole to accommodate this situation

If gas block comes off easily you can check the gas port dimensions as well as alignment

Sloppy bolt heads, carriers, gas key to gas tube fit are also common.

 

[Jeff Porter]

^^^*
This. The short stokes I had were related to the gas block being bored for a standard hand guard and using it on a floated barrel. The gas block was pushed back to the tenon on the barrel. When I gapped it about 0.025” it got enough gas to work.
Bore scope can show if it is line up or take some measurements and see if the center of the hole to the end of the gas block is the same distance from the tenon to the gas port on the barrel.
It also works the other way. If you are overgassed you can “turn down” the gas by moving the gas block off center and restricting the flow a bit. Poor man’s adjustable gas block.

 

[Old Navy]

I just bought an AR10 lower and 20" M5 upper in 6.5 Creedmore, both from Aero. It has a rifle length gas system. I assembled 20 rounds from components I had on hand, and the rifle will fire, eject the brass at 3:00 smartly, but will not go back far enough to strip off the next round, or lock back the bolt on an empty mag. The ammo I loaded was Starline virgin LPP brass, 41 grains RL15.5 under a Hornady 123 match bullet to 2.71" OAL. What would be your first course of action in correcting this problem? Thanks!

More powder or a different one. I had the same rifle you have. Mine shot 130 to 142s flawlessly with H4350. If you absolutely can't stand prosperity, install an adjustable gas block. Mine really really liked Berger 140 VLDs.

 

[Old Navy]

I am going to waste my money and try one box of factory ammo, just to use it as a baseline

Everyone that buys a gas gun should start with a box or two of factory ammo. I did and they all shot great.

 

[Lone Hunter]

I just bought an AR10 lower and 20" M5 upper in 6.5 Creedmore, both from Aero. It has a rifle length gas system. I assembled 20 rounds from components I had on hand, and the rifle will fire, eject the brass at 3:00 smartly, but will not go back far enough to strip off the next round, or lock back the bolt on an empty mag. The ammo I loaded was Starline virgin LPP brass, 41 grains RL15.5 under a Hornady 123 match bullet to 2.71" OAL. What would be your first course of action in correcting this problem? Thanks!

Here is a diagram I picked up years ago that is pretty accurate.