Correct length of gas tube for CMMG pistol position??

[eastern_hunter]

Guys,

Have begun to get an 8.5" 300 BLK upper running on an RR M16 lower.

Barrel is a pistol gassed 1:7 CMMG Wasp 8.5". Is threaded 5/8x24 from the factory.

Am using a YHM low profile steel gas block. Block appears to be properly centered over the gas port. I think I bought the pistol length gas tube from either Brownell's or BCM.

In initial firings with handloaded 225 gr Hornady OTMs, the rascal appears to be under gassed. Ejection is beyond 4:30. Being an M16, is not an option to go to a lighter carrier.

If I compare the exposure of the gas tube within the upper to the exposure of a carbine length tube inside the usual 11.5" upper ... the BLK tube currently in the upper appears to have 0.090 less exposure. This could cause the apparent undergassing.

Can any one please measure the OAL of a CMMG pistol length gas tube for me?

Thank you!

[Jim Timber]

What's the port diameter in the barrel?

[eastern_hunter]

Found a longer vernier caliper and was able to get a better measurement of the exposed gas tube inside the upper of the 8.5" ... is 0.936". Compares to 0.950" for a different upper. So I don't think that's likely to be the problem.

A rough measure of the gas port diameter is 0.096"

Will find a set of number drills to check it with.

Seems likely the gas port is too small. Is the nitriding of the barrel going to make it a challenge to redrill the port?

[tfbit]

NM. Didn't read original post well enough.

[Dolomite_Supafly]

What I did to correct a similar issue was take a carbine length gas tube and cut it down to where it was a little longer. And because it doesn't have the "bump" on the end it seems to help it seal better.

The way I did mine was I cut the carbine length gas tube about 1/4" longer than the pistol tube. The I loosely installed the gas block onto the barrel with the tube going through the receiver like normal. After making sure the gas tube will align with the key I let the bolt carrier go forward. I made sure to apply a little pressure to the gas block to ensure the end of the gas tube goes into the key as far as possible. When the bolt locks up the distance between the gas block and shoulder on the barrel is what needs to come off the end of the gas tube. Then I just take a die grinder and shorten the gas tube the rest of the way. I also radiused the edge like on a tube that hasn't been cut.

This ensure the gas tube is as far into the key as possible. This also makes sure you have a good seal.

My gun's specs are below in my signature.

Dolomite

[eastern_hunter]

I have a 16" Paladin bbl made from Douglas stock with his 3 way pistol position gas block. His tube is shorter and the barrel much, much longer after the port. Works beautifully w subs on the open setting and supers on the low gas flow setting. Has its own lower. Shoots subs to <1 MOA at 100 yards. I use it for hunting.

The 8.5" shorty for the M16 is the one currently being "birthed." I do not plan to use supersonic ammo with it and do plan to load separately for it.