Trying to diagnose a potential gas issue

[txgunner00]

There's no evidence of gas leaking from the key and it seems to be fastened well, at least I can't move it. Any chance the gas ports aren't lined up? A pipe cleaner passes through just like my other carriers.

I don't have a set of inside calipers but I'll try to measure the ID of the bolt channel tonight.

Here's some pics if they do any good.
IMAG2744.jpg
IMAG2739.jpg
IMAG2738.jpg
IMAG2740.jpg
IMAG2743.jpg
IMAG2745.jpg
IMAG2741.jpg

I took these with my phone so they aren't very good. I can get better ones if it will help.

[LRRPF52]

Did you say that this carrier causes the same problem in 4 other balsters? If so, that is weird. I can't see anything out of the ordinary with it, other than it appears that the key is not chrome-lined, but that is just the appearance in the pics. When clean, it is easy to tell a chromed carrier key from a non-milspec carrier key. It is chromed on the inside where the gas tube inserts on a milspec key. I didn't know this for a long time.

[Drifter]

At a glance, the wear at the base of the key doesn't look the same on each side. Perhaps normal, as I'm not looking at any of mine at the moment, but might be something to double check.

[txgunner00]

Did you say that this carrier causes the same problem in 4 other balsters? If so, that is weird. I can't see anything out of the ordinary with it, other than it appears that the key is not chrome-lined, but that is just the appearance in the pics. When clean, it is easy to tell a chromed carrier key from a non-milspec carrier key. It is chromed on the inside where the gas tube inserts on a milspec key. I didn't know this for a long time.

Yes. My 6.5, and a 20", 16" and two 10" .223 uppers. Would it be worth trying to replace the key? I'm pretty sure the key that's on it is not CL.

[txgunner00]

At a glance, the wear at the base of the key doesn't look the same on each side. Perhaps normal, as I'm not looking at any of mine at the moment, but might be something to double check.

Noticed that too but my other carriers are the same way.

[LRRPF52]

I would try replacing the key with a chrome-lined, TiN, or entire hard-chrome key, as long as the bolt recess chamber is chrome-lined, and within spec for ID. That is one of the most critical dimensions on the carrier.

Another problem that was encountered with a certain maker's carriers was that they were too wide at the raceways, and had a lot of drag in the upper, leading to sluggish cycling, reliability problems. Check the OD of your raceways (the only places where the carrier actually rides in the upper) against the OD of your other carriers.

Those are the 3 areas I would look at first:

Bolt recess ID
Raceway OD
Then carrier key replacement

[txgunner00]

Just following up on this...

Turns out one of the cap screw heads was torqued off but staked in place so it didn't come loose. I used an easy-out to remove the broken screw and replaced the key and screws with mil spec parts and it works just fine now.

[noone]

Whenever I think there is an issue with a gas system on a direct impingement rifle, the first thing I do is replace the gas rings just to make sure that isn't the problem. That little idea has rescued me from frustration many times.

[txgunner00]

That's one of the first things I looked at, but this bolt had fewer than 1000 rounds on it. This problem did remind me to check my 5.56 SBR and there wasn't much left of those. Replaced them before they became an issue.

[XcountryRider]

Anyone know what size hole should a 18in barrel have for a rifle length gas system?

[Drifter]

Anyone know what size hole should a 18in barrel have for a rifle length gas system?

~0.095" + or - 0.002" dependent upon other variables (ammo, buffer weight, buffer spring length & strength, BCG weight, etc).

An 18" w/ RLGS can be finicky when port size is down around 0.091"

[NugginFutz]

~0.095" + or - 0.002" dependent upon other variables (ammo, buffer weight, buffer spring length & weight, BCG weight, etc).

An 18" w/ RLGS can be finicky when port size is down around 0.091"

+1 on the potential for being finicky. That combo is one of the most finicky, due to dwell time being so short.

But then again, XC, you wouldn't be asking about gas port sizes if you didn't already suspect this.