308 AR Jamming

[NJRaised]

Aero 308 AR. 18” barrel, carbine buffer system.

Ran it for the first time today. Accuracy was about 1” consistently.

Now, running heavier ammo (168, 178, 175gr) the gun ran like a sewing machine. When I ran lighter ammo 147, 150, etc, the gun choked up. Ejected casings anemically, but wouldn’t pick up next round. Bolt went home on empty chamber, it also wouldn’t lock back on last round.

I know ar10s can be a little finicky. Is it normal to see this? The ammo it didn’t like was pmc bronze 147, NOSLER 150 grain, and Aguila 150 grain.

It cycled the hornady 168, Walmart special deer ammo 175, and S&B 168 flawlessly.

 

[alamo5000]

Find a lighter buffer and/or spring.

 

[jb0311]

Gas isn't enough to cycle the bolt all the way back. So you likely will need to lighten up your spring/buffer combo, or increase the gas that is cycling your bolt. Find the ammo you want to shoot, and tune the system to that. O

 

[NJRaised]

Are you guys aware of any buffer/springs that are lighter than the standard M5 carbine kit?

 

[jb0311]

Your buffer is probably somewhere around 3.8oz (weigh it to confirm). You might look at either sprinco springs or something like the odin adjustable buffer. You can essentially "tune" your buffer by using different material weights (Aluminum, stainless, tungsten). Or just find a carbine buffer that weighs less than your standard 3.8.

Sprinco also has a good guide to read to see what you might need for a spring.
link odin buffer
sprinco springs

 

[Rancid Coolaid]

I have posted this at least 10 times here, will continue to: AR10s are notoriously unreliable at first use. The trick is to overlube the BCG on breakin. If you think you have too much lube, you have almost enough.

If you have ever frog lubed a BCG, that helps immensely too.

Start with an exceess of lube, that might solve it immediately. If it does not, start playing with buffer setup.

For me, the lube has solved almost every AR10 reliability issue.

They are also notoriously overgassed, especially if suppressed.

Hope that helps.

 

[MrMcCrackin]

Had a friend with the exact same issue- Aero told him the upper was designed for a Rifle buffer tube, not a carbine.

He swapped out every single part on the upper trying to make it run correctly.

Ultimately what fixed the issue was tossed everything Areo, all that remains is Aero lower and carrier all other functional parts: barrel trigger, bolt, firing pin, buffer system have been replaced with non aero parts

 

[Cr1775]

Had a friend with the exact same issue- Aero told him the upper was designed for a Rifle buffer tube, not a carbine.

He swapped out every single part on the upper trying to make it run correctly.

Ultimately what fixed the issue was tossed everything Areo, all that remains is Aero lower and carrier all other functional parts: barrel trigger, bolt, firing pin, buffer system have been replaced with non aero parts

The upper has nothing to do with what spring and buffer you use,it's what length stock you use that determines whether you use rifle or carbine spring and buffer.

 

[Cr1775]

Any way another option is to use a JP silent capture spring and buffer.

 

[jb0311]

I have posted this at least 10 times here, will continue to: AR10s are notoriously unreliable at first use. The trick is to overlube the BCG on breakin. If you think you have too much lube, you have almost enough.

If you have ever frog lubed a BCG, that helps immensely too.

Start with an exceess of lube, that might solve it immediately. If it does not, start playing with buffer setup.

For me, the lube has solved almost every AR10 reliability issue.

They are also notoriously overgassed, especially if suppressed.

Hope that helps.

You're right there. I always assume people are properly lubing their AR's but that's a wrong assumption more times than not. I've got AGBs and JP SCS on all mine and never had an issue with large frames cycling suppressed/unsuppressed. They just require a bit more forethought when building your own vs small frame.

 

[Hecouldgoalltheway]

There are about 3 of these "my new ar10 won't cycle" posts a week.

Is it dripping with oil? New ar10's often require a bit of wear on the bearing surfaces before they will function well. Don't start tearing off parts yet. Do you have an adjustable gas block?

 

[PBWalsh]

There are about 3 of these "my new ar10 won't cycle" posts a week.

Is it dripping with oil? New ar10's often require a bit of wear on the bearing surfaces before they will function well. Don't start tearing off parts yet. Do you have an adjustable gas block?

I noticed this too on my new build. I have only dry fired it as of now, but the gun has lube literally seeping out of the cracks. But is smoothing in with the more I rack the bolt and continue the lube. Crazy how much more it needs than any small frame I’ve built.

 

[stanley_white]

I have posted this at least 10 times here, will continue to: AR10s are notoriously unreliable at first use. The trick is to overlube the BCG on breakin. If you think you have too much lube, you have almost enough.

If you have ever frog lubed a BCG, that helps immensely too.

Start with an exceess of lube, that might solve it immediately. If it does not, start playing with buffer setup.

For me, the lube has solved almost every AR10 reliability issue.

They are also notoriously overgassed, especially if suppressed.

Hope that helps.

In your experience, is this condition more prevalent in AR-10s using parts from different companies that are user assembled or AR-10s with all parts produced by one company or both?

-Stan

 

[Rancid Coolaid]

Because large format ARs aren't standardized, I usually buy complete guns rather than build. And with purchased guns, it is always an issue. I don't think it is as much about fit as the core long BCG design.

Someone that builds can chime in, maybe it is different.

For me the process is:
thorough clean when new
frog lube the bolt
lube with CLP or the like till it seems too much, then add a little more.
throw lead
be happy

 

[TonyTheTiger]

Doesn't sound like the gun is jamming at all.

 

[Cr1775]

Sounds like not enough gas, maybe friction with the bcg, raised bur or something to heavy buffer or to strong of spring, hell can't remember did he have a agb maybe he has to open it up, or maybe like someone else said he needs to clp the shit outta it.

 

[mtrmn]

New large frame AR. Pull the BCG and SUBMERGE it in Mobil 1 overnight. Pull it out of the oil and allow it to drain the excess runoff. Re-assemble and run a couple hundred rds of ammo through it. This is the only way I know to get the message across that these things need to be over-lubed until they get broke in. The internals (where the gas rings live) of the BCG need oil just as much as the external rails. Put at least 2-300 rds through it before you start throwing more parts at it. And report back with results and ask questions too.

 

[kriller134]

Sell it and get a seekins or JP

 

[Jsp556]

Lube the bcg.

Even after the gun is broken in, the AeroM5/DPMS Carbine set up is the most problematic buffer setup to use on a large frame. Swap it over to the Armalite AR10 carbine RE kit.

If you’re running an agb, open it up until it functions with the weakest ammo you’re going to use.

Good luck.

 

[NJRaised]

It’s actually my friends rifle. We put about 100 rounds through it today.

Will soak the bcg in lube and run it again.

Will report back.

Ar10s are a new animal to me, I have a ton of experience with ar15s, along with 6 different armorers certs from respected companies. This is large frame is new to me. Appreciate the help!

 

[PBWalsh]

Because large format ARs aren't standardized, I usually buy complete guns rather than build. And with purchased guns, it is always an issue. I don't think it is as much about fit as the core long BCG design.

Someone that builds can chime in, maybe it is different.

For me the process is:
thorough clean when new
frog lube the bolt
lube with CLP or the like till it seems too much, then add a little more.
throw lead
be happy

So I have a basic Aero BCG in mine, from the factory packing. It is shipped with no lube AT ALL. It is extremely dry and requires a pool of lube to cycle well. So to reiterate the above, dunk it in oil.

Hope it all works this Saturday during first shots.

Speaking of, I am running an SLR Sentry 7 block. Do y’all start fully closed to tube the gas or a few clicks open?

 

[bfoosh006]

As mentioned, lube it well.

And give it more time to break in.

 

[KYAggie]

Don’t have to read through all th responses, but in my experience, 2 AR10’s, a adjustable gas block is required on a AR10. In your case, you need more gas it seems, so a lighter buffer and spring combo or a lighter bolt carrier is also needed. Start there and get a AGB and tune to your load. For AGB’s look at SLR and Riflespeed. The Riflespeed ones do not need a tool to adjust which is very nice.

Mine are both lightweight builds so I have titanium bolt carriers, Tacom .8 oz buffer, heavy weight spring, and AGB. If I mess up and open the gas block all the way I would destroy something, I have to tune every load, but it’s as soft shooting as a 223 because I’m not slinging a bunch of mass.

 

[r.tenorio671]

So I have a basic Aero BCG in mine, from the factory packing. It is shipped with no lube AT ALL. It is extremely dry and requires a pool of lube to cycle well. So to reiterate the above, dunk it in oil.

Hope it all works this Saturday during first shots.

Speaking of, I am running an SLR Sentry 7 block. Do y’all start fully closed to tube the gas or a few clicks open?

....SLR advises to open fully for the 1st round, then adjust until lock-back occurs consistently....

 

[hlee]

Start with the block full open and work back until you get a failure to lock back, then open a couple of clicks. If you start at full closed on the first shots from a new gun, it is possible you may need to mortar the gun to get it to eject. This has been my experience on my last 2 rifles, adjusting the block starting at closed.

 

[RUTGERS95]

Had a friend with the exact same issue- Aero told him the upper was designed for a Rifle buffer tube, not a carbine.

He swapped out every single part on the upper trying to make it run correctly.

Ultimately what fixed the issue was tossed everything Areo, all that remains is Aero lower and carrier all other functional parts: barrel trigger, bolt, firing pin, buffer system have been replaced with non aero parts

shouldn't matter, it's weight of the buffer, not length. I always run heavy carbine buffer set ups with my aero builds and zero issues.
OP should play with buffer weights imho or put an adjustable block on there. I didn't see that he did that.

with 308 builds, i try to keep as much from same company as possible. I've been incredibly lucky with my aero builds, zero issues but we all know it's a tricky game with them

 

[mtrmn]

Lube the bcg.

Even after the gun is broken in, the AeroM5/DPMS Carbine set up is the most problematic buffer setup to use on a large frame. Swap it over to the Armalite AR10 carbine RE kit.

If you’re running an agb, open it up until it functions with the weakest ammo you’re going to use.

Good luck.

AR15 carbine buffer weights:
normal -- 3.0 oz
H or H1 -- 3.8 oz
H2 -- 4.6 oz
H3 -- 5.4 oz
These are for AR15s.--NOT 308s.
The minimum weight required to handle 308 recoil is normally H3 or 5.4 oz. Coupled with a heavier spring for 308, not 5.56. Most M5/DPMS 308 buffer setups come with an AR15 buffer tube and a shortened (2.5") buffer at 3.0 oz and they expect it to somehow handle the full recoil of a 308 when that setup is many times barely adequate for a 5.56. If you want to eliminate this glaringly inadequate recoil system in your quest for reliability, the above-mentioned Armalite kit, PN AR10REKT01, is the easy button.
The internal depth of the Armalite tube is 7-5/8" so it can use the NORMAL LENGTH BUFFERS WHICH ARE 3.25". It will come with the proper spring and H3 buffer.
The original buffer tube you have is most likely only 7" in internal depth for an AR15 and they had to shorten the buffer to give the 308 BCG enough travel. That's why the buffer is only 2.5" long. These buffer/tube combinations cannot be mixed/matched.

IF your gun still won't run after all the oil and breakin, then this would be my starting point. I'd go ahead and get the properly designed buffer system on the gun, then work from there, knowing the gun SHOULD RUN with your buffer setup. Remember that your objective is RELIABILITY at this point.

All that being said, They may have compensated for the light duty recoil system by drilling the barrel gas port too small. It may need to be opened up a tiny amount to get the proper amount of gas for good operation.
I'm assuming you DO NOT have an adjustable gas block, and if you do have one your running it wide open. Your problem sounds like it's undergassed right now.

This also reminds me, if you have a gas block that clamps on or attaches with set screws, check to make sure it has not moved out of proper position.

​

 

[PBWalsh]

....SLR advises to open fully for the 1st round, then adjust until lock-back occurs consistently....

Start with the block full open and work back until you get a failure to lock back, then open a couple of clicks. If you start at full closed on the first shots from a new gun, it is possible you may need to mortar the gun to get it to eject. This has been my experience on my last 2 rifles, adjusting the block starting at closed.

Thanks, I just went and opened it fully so I wouldn’t forget.

 

[Gustav7]

AR15 carbine buffer weights:
normal -- 3.0 oz
H or H1 -- 3.8 oz
H2 -- 4.6 oz
H3 -- 5.4 oz
These are for AR15s.--NOT 308s.
The minimum weight required to handle 308 recoil is normally H3 or 5.4 oz. Coupled with a heavier spring for 308, not 5.56. Most M5/DPMS 308 buffer setups come with an AR15 buffer tube and a shortened (2.5") buffer at 3.0 oz and they expect it to somehow handle the full recoil of a 308 when that setup is many times barely adequate for a 5.56. If you want to eliminate this glaringly inadequate recoil system in your quest for reliability, the above-mentioned Armalite kit, PN AR10REKT01, is the easy button.
The internal depth of the Armalite tube is 7-5/8" so it can use the NORMAL LENGTH BUFFERS WHICH ARE 3.25". It will come with the proper spring and H3 buffer.
The original buffer tube you have is most likely only 7" in internal depth for an AR15 and they had to shorten the buffer to give the 308 BCG enough travel. That's why the buffer is only 2.5" long. These buffer/tube combinations cannot be mixed/matched.

IF your gun still won't run after all the oil and breakin, then this would be my starting point. I'd go ahead and get the properly designed buffer system on the gun, then work from there, knowing the gun SHOULD RUN with your buffer setup. Remember that your objective is RELIABILITY at this point.

All that being said, They may have compensated for the light duty recoil system by drilling the barrel gas port too small. It may need to be opened up a tiny amount to get the proper amount of gas for good operation.
I'm assuming you DO NOT have an adjustable gas block, and if you do have one your running it wide open. Your problem sounds like it's undergassed right now.

This also reminds me, if you have a gas block that clamps on or attaches with set screws, check to make sure it has not moved out of proper position.

​

This ^^^ is the only info you need besides a lot of lube.

If you’d like even more info, go look around on 308AR forum. Those guys know AR10’s well and have a lot of experience fixing commons issues with home builds, Aero’s, PSA’s, etc

You need to look at your rifle as if it’s something completely different than an AR15.

1.) Correct Buffer setup for an AR10
2.) Lube
3.) Gas port size (should be around 0.93” depending on barrel type)

If you want to keep your ar15 buffer tube you can get the correct 2.5” buffer weights through heavybuffers.com . They special make the shorter ones to the correct weight and with correct 308AR springs.

 

[mtrmn]

This ^^^ is the only info you need besides a lot of lube.

If you’d like even more info, go look around on 308AR forum. Those guys know AR10’s well and have a lot of experience fixing commons issues with home builds, Aero’s, PSA’s, etc

You need to look at your rifle as if it’s something completely different than an AR15.

1.) Correct Buffer setup for an AR10
2.) Lube
3.) Gas port size (should be around 0.93” depending on barrel type)

That should read 0.093" obviously. And I agree with the 308AR forum. Just don't ask a bunch of questions before you do a lot of READING.

 

[Gustav7]

That should read 0.093" obviously. And I agree with the 308AR forum. Just don't ask a bunch of questions before you do a lot of READING.

Hahaha, big thumbs on a small phone. A 0.93” gas port is called an SBR.