Mid-length ejection angle

[prepare]

It was doing that on my carbine lower but not on my A5 H2 lower.

If the carbine lower has a carbine buffer then I suggest an H buffer or an H2 with a Sprinco Blue spring.

[1168]

If the carbine lower has a carbine buffer then I suggest an H buffer or an H2 with a Sprinco Blue spring.

Why would a stiffer spring and heavier buffer help? Thats literally the opposite of what he needs.

OP, from your borescope pictures, it does look like your gas port is partially occluded. You say the barrel was pre-dimpled…. If you remove the rear set-screw while leaving the block cross pin in place, is the screw hole centered over the dimple? If it is not, you can remove the cross-pin, push the block back a hair until the dimple lines up, and install some set screws, properly. I’d suggest the toothed ones that BRT sells and some Rocksett. You’d be living without the cross-pin in this scenario.

I suspect your gunsmith effed up. Or the barrel maker effed up. Either way, someone effed up pretty significantly, because with the size of the hole in most gas blocks, a drunk Bonobo can get the holes to line up 99 times out of 100, with one hand on his pecker, not even using a jig.

You might be able to keep shooting it in whatever carbine RE config works and use full-pressure ammo, preferably 62 gr and up, and see if it still is reliable when it gets dirty and the temp is low. It probably is very close to the ragged edge if it won’t run an A5H2, though. The fixes I can think of if it ceases to be reliable would require some skill and access to tools, but it can be salvaged.

But I also think it would be reasonable to just bring it back to the gunsmith like Vicious CB pointed out, at this point. Because someone took your money and effed up, and it wasn’t your fault.

I feel your pain.



Edit: I just looked again at your pics…. Is the hole in the gas block ovoid and smaller than the gas port, or am I going blind?!? That would be pretty strange. Have you taken the gas block off and looked at that?

[opngrnd]

Would it be possible to enlarge the gas port hole in the gas block? Seems like that would let him keep the pinned gas block and solve his gas drive problem.

[lysander]

Would it be possible to enlarge the gas port hole in the gas block? Seems like that would let him keep the pinned gas block and solve his gas drive problem.

There is not enough mis-match between the two ports the to cause a problem.

[MistWolf]

Why would a stiffer spring and heavier buffer help? Thats literally the opposite of what he needs.

A stiffer spring may not be needed or even desirable (but blue springs have long been known to work) but a carbine buffer is too light with standard ammo, regardless of how the AR is gassed.

from your borescope pictures, it does look like your gas port is partially occluded...

I watched the video a few times. The gas port is not blocked

You might be able to keep shooting it in whatever carbine RE config works and use full-pressure ammo, preferably 62 gr and up, and see if it still is reliable when it gets dirty and the temp is low. It probably is very close to the ragged edge if it won’t run an A5H2, though.

Gas port size does NOT determine which buffer is to be used. Using an adjustable gas block, I performed experiments with Carbine, H, H2 and A5H2 buffers. Each buffer required the the same gas block setting to achieve full lock back, both unsuppressed and unsuppressed, using standard 5.56 ammo.

I just looked again at your pics…. Is the hole in the gas block ovoid and smaller than the gas port, or am I going blind?!? That would be pretty strange. Have you taken the gas block off and looked at that?

You aren't seeing the port in the gas block. The port in the gas block is larger than the gas port in the barrel. What you are seeing is the wall thickness of the barrel where the gas port passes through.

Of course the gas port is going to look oval. It's drilled through a circular tube.

The assembler didn't screw up the gas block installation.

[Curlew]

When I was using the A5 system it was the intermediate buffer tube with a green sprinco rifle spring. A5-H2 buffer.

You might try running the A5 with a standard rifle spring. The Sprinco green isn’t advertised as extra-power, but at least based on my sample, it is stiffer than baseline.

Also, the discussion so far has considered pretty much every possibility except the gas port itself. Any idea of the diameter? Maybe it’s just too small….

[Wow]

I sent my upper to criterion. They were nice enough to pay for shipping. Hopefully they find the issue if there is one.

@prepare stiffer spring and heavier buffer would only worsen my problem. If anything I'd need to get a lighter buffer and a yellow spring. But that seems more like a bandaid than a solution.

@1168 I also think the hole in the gas block is smaller than that of the barrel. Also a bit oval shaped.

@opngrnd probably possible but I'd just buy a new one at that point.

@lysander alignment looks good but the gas block seems to have the smaller hole.

@MistWolf Agreed with everything. Still not sure why it would look oval if it was drilled through a circular tube? A circular drill bit should leave a circular hole no matter the shape of the object it was drilled into, would it not?

@Curlew. I'll try that. My sprinco green rifle spring does feel a bit stiffer than my generic rifle spring.


Here are some pictures of the borescope down my BCM barrel and BCM gas block.

blob:https://imgur.com/219b7c86-c989-45c2-b034-773b05803987

[1168]

A stiffer spring may not be needed or even desirable (but blue springs have long been known to work) but a carbine buffer is too light with standard ammo, regardless of how the AR is gassed.


I watched the video a few times. The gas port is not blocked



Gas port size does NOT determine which buffer is to be used. Using an adjustable gas block, I performed experiments with Carbine, H, H2 and A5H2 buffers. Each buffer required the the same gas block setting to achieve full lock back, both unsuppressed and unsuppressed, using standard 5.56 ammo.



You aren't seeing the port in the gas block. The port in the gas block is larger than the gas port in the barrel. What you are seeing is the wall thickness of the barrel where the gas port passes through.

Of course the gas port is going to look oval. It's drilled through a circular tube.

The assembler didn't screw up the gas block installation.

Look past the inside of the gas port. It looks like you can see the edges of the gas block hole, but in both the front and the back. I could be wrong; I’m looking at it on a tiny phone.

Did you notice his gun won’t cycle with an A5H2, but it will cycle with his carbine buffer? I’d say thats pretty good evidence that more spring and weight are a poor plan.

[MistWolf]

Look past the inside of the gas port. It looks like you can see the edges of the gas block hole, but in both the front and the back. I could be wrong; I’m looking at it on a tiny phone.

@1168 I also think the hole in the gas block is smaller than that of the barrel. Also a bit oval shaped.

Looking at it zoomed in on a 12 inch laptop screen, I can see there is no edge of the gas block visible. If the gas block were blocking the barrel gas port at all, it would show up as a step at the bottom of the barrel gas port.

Did you notice his gun won’t cycle with an A5H2, but it will cycle with his carbine buffer? I’d say thats pretty good evidence that more spring and weight are a poor plan.

First, when using standard ammo, a carbine buffer is too light. Let me say that again- When using standard ammo, a carbine buffer is too light.
Second, when using standard ammo, an A5H2 is just right. It's not too heavy. It's not too light. It's the same weight as a rifle buffer.

Therefore, using standard ammo, if the AR cycles with a carbine buffer, but not with an A5H2 (assuming correct spring & receiver extension for both are being used), we can draw two conclusions-
-First, not enough gas is getting to the expansion chamber to operate the AR.
-Second, the AR is barely functioning with the carbine buffer.

So, sticking with a carbine buffer when using standard ammo is a poor plan. A better plan is tracking down the gas flow problem.

We know (at least I know) the gas block isn't blocking the gas port and therefore, isn't the problem.

My guess is the gas tube knob that fits in the gas key is too small and/or the gas key leaks at the carrier. I'm not going to go back and look because I've already wasted too much time on this thread, but I believe a different carrier was tried with the same results. That narrows it down to the gas tube knob.

A hole drilled through the sidewall of a round tube looks- let me emphasize the word looks- oval because the sidewall of a round tube is not flat.

Fun fact- Holes drilled at any other angle than 90 degrees to a flat surface, look oval.

The only part of a hole that's 90 degrees to the surface when drilled into the side of a round tube is the centerline running along the length of the tube. The further the diameter of the hole is from that centerline, the further from 90 degrees it is to the surface. It's gonna look oval.

I suspect my post on the matter is going to be dismissed. So from here, you guys are on your own.

Wow, Criterion should get you straightened out.

[Wow]

Got my upper back from Criterion.

They said the two BCGs I was using were bad. At least the bolts were. They gave me a free BCM bolt. Gas block, ports, etc was all fine. They said Sharp's BCgs are trash.