Please help. My AR10 is short stroking.

[fatelvis]

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.

Here are two pics of the gas port. It’s hard to see into the hole and see if it’s aligned.

 

[GaryL1959]

Just a thought...too much gas, buffer too light, spring too light / underpowered. Sounds backwards, but these will cause the bolt to out run the magazine. In other words, the bolt cycles faster than the magazine spring can push the next round up to be stripped and fed into the chamber.

 

[Richard Jones]

Will it lock back on an empty mag by hand? Buffer too long/spring too long/thick.

Tried different mags?

 

[dantiff2]

Keep it simple. My first go would be to pull the bolt assembly out and lube the snot out of it. grease on the cam pin and bolt lugs. Cycle the weapon by hand a bunch and then to do as you said and try some factory ammo to verify that it does in fact function correctly. These guns NEED broken in! If it doesn't run (lock back) with factory stuff then I'd contact Aero and see where they suggest to start diagnosing the problem. They may want it back before you even try to "fix" anything. My first inkling would be to lower the bolt carrier mass or in your case a lighter buffer weight. If that still doesn't work, try a different buffer spring.
Dan

 

[shoobe01]

People say this, but I have seen tons of guns that run like a swiss watch and do not conform to this.

Personally, my SBR is a 2:00 ejector but runs with the same spring and buffer for any upper at all. 9 mm, 300, 5.56, suppressed or not, etc. For years, many thousands of rounds. Cold and sandy and after immersion and everything. Why? Shrug. I have been advised by armorers:

Running is running.

Take the W when it happens and don't ask too many questions or you'll jinx it

 

[Steve morgan]

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

Be careful, my ar10- 6.5 c factory ammo was not crimped. When it stripped out of the mag,trying to load the bullit pushed back into the case.

 

[338 Mollett]

Pull the charge handle all the back to see if the bolt clears the release catch. If it does you have a gas issue. If you have an adjustable gas block close it half way so you can see it through the port as to alignment .If no bores scope use a piece of spaghetti to line it up.

 

[shoobe01]

Here are two pics of the gas port. It’s hard to see into the hole and see if it’s aligned.

Normally is pretty easy to see up there, shiny and stuff.

Try light from outside? Not too hard or destructive to remove the gas tube, then shine a light and it should reflect enough you can see with the borescope and get an idea if lined up or not.

(Somewhere I have photos of several of these, even on other gas operated guns but I cannot for the life of me find any to use as examples of how it should be easy to see!)

 

[Twdmar]

Just a thought...too much gas, buffer too light, spring too light / underpowered. Sounds backwards, but these will cause the bolt to out run the magazine. In other words, the bolt cycles faster than the magazine spring can push the next round up to be stripped and fed into the chamber.

I had a similar problem with a 308, using an aero BCG. A lot of the 308 barrels are over gassed and because there is a lot of gas, the bolt is trying to move out of battery before the brass case has had a chance to let go of the chamber walls.
I cannot speak to the creedmoor bolt(if it's different) but that's is part of the reason the extractors have such heavy springs and have a tough time going into battery as well.
If the rifle is overgassed, and I'm assuming it's a rifle length gas system, different powder may be a good choice.
The OP used Re 15.5 and I don't know if that would be the right powder or not. For 20" 223 ARs, Re15 was great, but AR comp caused short stroking in a lot of them. They are supposed to be very similar powders but gas pressure is obviously different. It may be at play here too. AR10s are definitely not as plug and play as the little ones.

 

[RussellJ]

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!

My first AR rifle was a DPMS 6.5 Creedmoor and had the same issue. Long story short is that the bolt gas rings need to be seated, aka broke-in. If you remove the bolt carrier unit and cycle the bolt by hand, if feels gritty or not smooth. Place it in a Ziploc bag with lots of oil and cycle the bolt head by hand while watching tv for a few evenings or you can shoot a couple of hundred rounds though the rifle. It fixed my rifle.
Added note: Back when this happened, I called DPMS and was told that that I could send the rifle back to DPMS for service and he explained that an AR-10 vrs AR-15 is like comparing an F150 pickup to a F350 HD Truck. The rifle just needed to be shot. Being a cheap ass, I came up with the bolt carrier in the bag with lube concept.

 

[jelenko]

I'm still on it's a brand new rifle => the vendor should sort it out.

 

[Fast14riot]

I'm not an AR10/LR308 guy, but I've built several unconventional AR15 and have had some nagging tune issues. These are areas I have found to be of concern on any new build with issues. I now check each of these on any new or existing build with issues.

First thing I would do, remove gas block and look for evidence of misalignment (is the carbon ring nearly centered over the gas port).

Strip the upper of all lube, cycle it dry a few hundred times while sitting in front of the TV. Clean the BCG and upper and do it again. Anodized aluminum doesn't run very smooth on like material. This will pre-wear/break in the moving parts.

Check for excessive round height from the magazine, may need to tweak feed lips to raise or lower next round.

I alway put a drop of blue loc-tite where the gas tube enters the gas block. This is a significant source of gas leakage. When building, I use a couple drops on the gas journal to bed/seal the GB even better.

If using a BAD lever, is it hitting the inside of the trigger area when cycling?

Remove the upper, check the gas tube entering the gas key, when cycling slowly by hand is it pushing the gas tube in any direction? If so, its misaligned. Can carefully tweak it by hand for proper alignment.

Running a mag or two of factory ammo is always a good idea to get a known baseline.

Do not start switching buffers/springs until all of this has been checked and confirmed. It'll save you the money.

 

[Coyotefurharvester]

Since it fires but will not cycle the next rd or lock open on empty mag, gas bolt(bcg) needs to be checked that it was torqued and staked correctly. Gas tube, block must be installed correctly.

 

[Old Navy]

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

Right on!

 

[chop house]

The OP used Re 15.5 and I don't know if that would be the right powder or not. For 20" 223 ARs, Re15 was great, but AR comp caused short stroking in a lot of them. They are supposed to be very similar powders but gas pressure is obviously different. It may be at play here too.

some time ago i posted a question regards muzzle pressure of faster vs slower powders and varying bullet weights. the issue was vaguely similar. i won't muddy up this thread, for me the best way to work out the problem was test the rifle with the intended factory ammo. only then start experimenting with what i could control in the reloading process.

btw, that project is what bumped me off the fence in downloading and 'learning' gordon's reloading tool...

 

[DocBII]

fatelvis,

An inexpensive solution may be to add 1 piece rings in place of the 3 piece rings. Fixed similar problems in AR10s and AR15s. 3 piece rings would align the gaps and allow too much gas pressure drop.

HTH,
DocBII

 

[Woofie]

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

I use my borescope. The light lets you see whether everything is lined up very well.

 

[dantiff2]

fatelvis,

An inexpensive solution may be to add 1 piece rings in place of the 3 piece rings. Fixed similar problems in AR10s and AR15s. 3 piece rings would align the gaps and allow too much gas pressure drop.

HTH,
DocBII

 

[Fast14riot]

Oh, one step I forgot to add, if you have a modern smart phone, film the action cycling in slow motion. You would be amazed how much you can see going on that way. Also, try a different magazine. Sometimes the spring might not be enough to push the bolt stop up fast enough after last round.

 

[asquared19]

I had a similar issue. Ended up being 2 things. One was alignment on the upper and lower. Second was conflict on the cheek weld riser and charging handle.

1) remove buffer tube and spring. Hold the rifle with the barrel up. Charging handle should freely drop to full back position. Mine would bind up part way back. If I tapped it, it would drop. Ultimate fix was a replacement lower.

2) my cheek riser would conflict with my ambi charging handle. Fix will be cutting about 1/4" off the front of my cheek riser. Temp fix is just having it set a little lower then I prefer.