I am having a failure to chamber a round. I can shoot 5, 6 or even 10 with no issues but then a round get stuck and the bolt actually bends it. I clear this and it is good far a few more rounds.

I have another 308 AR that works flawlessly. I swapped the lower half from my good gun and the problem stays with the upper. So I am sure it is not with the lower, buffer or buffer tube.

I am using commercial ammo. I have tried .308 PMC bronze 147gr FMJBT and 7.62x51 PMC X-TAC 147gr FMBT.

Here is the build:
Upper receiver - Aero precision
Barrel - Criterion M110
BCG -  AIM Surplus
Gas Block -  ODIN works low profile

I have:
Swapped lower halfs and BCGs with a functioning gun. Problem was still present.
Removed the ODIN works adjustable gas block and replaced with a standard low profile ODIN works gas block. No change in function
Tried Magpul Pmag 20 and 25 round magazine. No change in function.
Tried Pro-Mag 20 round magazine. No change in function.

I see the barrel has much deeper feed ramps than the upper receiver. I am thinking of matching them. I have a mill so this is not hard to do. The only thing holding me back is my other gun's upper is the same and does not do this. I bought them at the same time.

I have it narrowed down to one of 3 things:
Feed ramps.
Magazine.
Ammo

Any ideas from the group would be helpful. Thank you.

That's called a bolt over base malf, where the bolt carrier is actually pushing the cartridge, not the bolt.

It normally happens when you don't have enough gas, but can also be when there is too much gas and cyclic beats the cartridge stack lift capability of the magazine spring.

Since it isn't present in your other gun, and is present on the working gun's lower, that points to your gas system most likely.

Check that your gas tube is long enough.

What is the port diameter on your M110 barrel?

Criterion/Fulton are higher quality than most and they use correct gas ports in my experience.

Check that your carrier key isn't loose.

Seems like you're not getting enough gas to cycle fully to the rear, then the BCG is coming forward without getting the bolt behind the cartridge head.

What extension tube (buffer tube) length and what buffers are you using?

Are they the same?

The barrel is a 20" barrel with a rifle length gas system. I did check the length of the tube and it measures just over 15". I did not measure the gas port. I do know it is clear because I checked with a drill but did not check for size.

I will check the carrier key but I tried the BCG from my other gun and had the same issue so I pretty much ruled out a BCG issue.

I am running an A2 stock. I bought the setup from KAK Industries as a 308 kit. It has A2 receiver extension and supposedly a 308 rifle buffer and spring.

I am pretty confident that my gas system is not the issue unless the port is too small. I check port alignment and made sure the tube hole lined up with the hole in the gas block.

When I had the adjustable gas block on I adjusted the gas until it would lock the bolt open on the last round. I usually do 5 single round checks to make sure the bolt holds open. So it was going back far enough. I did not try it today thought.

My other gun has an 18" barrel with mid-length gas and a collapsible stock.

I have a slow motion video of the gun firing. I can post it to drop box if you want to watch. Send me a PM.

Is there such a thing as a heavy buffer for 308 rifles?

One other thing of note. In the slo-mo video after a round was fired there was some flame in the upper receiver. Not sure it means anything. We did not see it when shooting but it is in a few frames of video.

I'm saying it's feed ramps

I had that same issue a few weeks ago, opened up the adjustable gas block a few more clicks and issue went away. I think too little gas will cause this.

@TBone556 - I will remove the gas block and verify the gas port in the barrel is the correct size. If this is good then I will match the feed ramps on the upper to the barrel. I can do this pretty easily on my mill.

@rock_star - The adjustable gas block was replaced with a standard gas block for test purposes.

You are not getting enough gas.
Bolt-overs are usually a sign of slipped gas block, or low power ammo.  The "Big" platform AR's have heavier carriers that need to move further back, ANY loss of the essential gas will give you that textbook Bolt-over

Wouldn't a gas issue be repeatable with every round?  If there is not enough gas there shouldn't be enough gas with every round fired no?  Why would 5, 6, or even 10 rounds fire without issue and then all of sudden a round gets stuck if it was a gas issue?

Just curious how the not enough gas meshes with the fact that he can shoot 5, 6 or even 10 with no issues but then a round get stuck.

Increasing friction as the gun warms up and throws off its lube. If it's barely cycling from the get go, then it's going to be very sensitive to that. And the chamber being a little rough. Or any number of other issues.

Mine did the exact same thing, problem was i set the adj. gb using remington ammo then when i switched to pmc (lighter charged ammo) problems occured.

When you are using the standard gas block will the bolt lock back every time on an empty mag?

Also, I see some fouling on the top of your bolt. Have you checked the gas key thoroughly? Look for leakage at the gas key.

I did not look at the BCG for gas leak because I swapped a BCG from a fully functioning gun into this one and had the same issue. Next time I go out I will triple check the gas key.

With the standard gas block I verified the hole lines up and the tube is clear. I double checked the length and it is correct for rifle length gas.

With the standard gas block I loaded one round in 4 different magazines and the bolt locked back on each one. I did this test twice.

I was using PMC Bronze 147gr .308 and PMC X-TAC 7.62x51 147gr. I plan to grab some different ammo to try. Maybe the PMC is just under-gassed and does not always push the BCG back far enough when hot?

I did finally get some time this week to check the feed ramps. The tip of the bullet actually hits the tiny ramp on my upper. I did open them up a little bit more. My other gun has the exact same upper receiver. I bought them at the same time from Brownell's.

I hope to get to the range in the next week or so.

Lastly the only things different between my functioning gun and this one are the barrel and the receiver extension/buffer combo. My functioning gun has a 16" mid length gas barrel and carbine receiver extension/buffer, this has a 20" rifle length and A2 receiver extension/buffer..

I finally had time and co-operative weather to go to the range and test my gun.

I opened up the gas port from .093 to .096. The gun still has the bolt over round feed failure.

I have another gun with rifle length gas I built for my son. His gas port is .101" and it works with any ammo I feed it. I am going to open up the port to .101". I will then run 200 rounds through it regardless if it still has a feed issue just to rule out break in as the cause.

I am going to pick up some different ammo this week to try and see what happens.

This picture is a frame grab from a slo-mo video. This is the point at which the bolt is furthest back before the feed failure. You can see the bolt is not far enough back

I opened up my gas port to .102". I was able to shoot 100 rounds of M80 ammo with not one issue. I am happy.

Thanks to all who provided ideas.

That top pic with the round jammed at an angle is EXACTLY what I was getting with a way under-gassed rifle. Still working on the problem, but too little gas (in my case due to a bad tube) gave precisely this.