Tell me what I'm overlooking.

[amac]

Gas starts with the ammo/round that’s fired. I second the opinions of don’t drill until you’ve tested full factory ammo.

I’m having a similar issue and was using UMC ammo. Before buying anything, I’m going to try quality ammo.

[26 Inf]

Gas starts with the ammo/round that’s fired. I second the opinions of don’t drill until you’ve tested full factory ammo.

As I indicated in my OP - I've shot a lot of this ammo over the years - it was out training ammo at work, since I retired I've had to buy my own, but I'm well on my way to filling a second five gallon bucket with brass from this manufacturer.

I don't plan on using the rifle for 5.56 or suppressed, so I'll figure it out and get it to run.

[amac]

As I indicated in my OP - I've shot a lot of this ammo over the years - it was out training ammo at work, since I retired I've had to buy my own, but I'm well on my way to filling a second five gallon bucket with brass from this manufacturer.

I don't plan on using the rifle for 5.56 or suppressed, so I'll figure it out and get it to run.

Understood. However, for $5 and 20 rounds, you can rule ammo out of the equation.

Good luck.

[amac]

As I indicated in my OP - I've shot a lot of this ammo over the years - it was out training ammo at work, since I retired I've had to buy my own, but I'm well on my way to filling a second five gallon bucket with brass from this manufacturer.

I don't plan on using the rifle for 5.56 or suppressed, so I'll figure it out and get it to run.

Understood. However, for $5 and 20 rounds, you can rule ammo out of the equation.

Good luck.

[jsbhike]

Understood. However, for $5 and 20 rounds, you can rule ammo out of the equation.

Good luck.

I vote for trying full power 5.56 first too. I am betting you get proper cycling, but if not then you likely rule out port size as the issue.

[jpmuscle]

Mil spec gas tube and not something undersized and out of spec?


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[26 Inf]

Thanks all for your suggestions.

Fixed it.

The BCG I was using was a semi-auto one I built from a kit provided from Brownell's years ago. As I mentioned in my OP, it functioned fine in the 16inch carbine length upper I tore down to get my favorite MI rail off of for this build.

When I first had problems I did the standard 'will the bolt carrier descend upon it's own weight' check for the gas rings and examined the gas/carrier key for signs of venting - nothing.

Anyways, I thought maybe the miniscule difference in weight might make a difference, so I took a new Toolcraft out of the parts hoard and it works fine - did numerous lock back checks, did a rapid fire mag dump, and then zeroed the rifle at 100 yards and shoot the rest of 3 mags at 100 and 200 yard plates.

I did not take another rifle out to see if the BCG worked in it, but this BCG came out of the first rifle I built, and it has one my heaviest used rifles. It functioned fine.

Oh, well. I'll check tomorrow with the semi-auto carrier in another mid-length to see if it functions.

[26 Inf]

.0748" is a standard drill size (1.90mm), so that's probably what it is now.

Sometimes a brand new barrel can have a little bit of a sharp edge or burr on the gas port entrance that slows down the flow a little.

Some shooting usually smooths this out and increases gas drive slightly.

This may only be notable when the port is on the small side of the normal range, as it is in this case.

Clint, this may have been what is going on.

What brand barrel?

It is a Rosco PureBreed 13.7 in stainless. It is pinned right at 16.1.