Educate me on gas tube length, gas block holes, etc.

[Fudmottin]

My barrel maker was kind enough to test fire my barrel so that it would cycle with the gas port in the pistol position and an adjustable gas block that has three positions: High, Low, Closed.

I haven't busted the cherry on it yet. Been too busy. But when I do, the first person to get feedback will be my barrel maker. I will probably also post here.

BTW, my barrel is threaded in the 5/8-24 standard for 30 caliber barrels. That makes getting a commercial can much simpler.

[steezo757]

I'm also trying to decide the proper gas port size. I have a Noveske 10.5" barrel with the gas port in the pistol position. And have not been able to work up a load that's accurate and cycles, so I had a local gunsmith in VA (when I lived there) open up the gas port to 0.107". I've read recommendations that anywhere from 0.085" to 0.125" will cycle with subsonic rounds.

First off, are there gas tubes with a I.D. of 0.125"? I thought the normal gas tube I.D. is around 0.110". I'm thinking about having a 3 postion gas block made by tp555. From what I understand I can select two gas port sizes with the 3rd position being off. I want to run only subsonic. Does anyone have any recommendation for the two gas port sizes? Again, I only want to run subsonic.

This AR platform is becoming a little fustrating. I'm also working on a .300/.221 bolt gun and am considering just focusing on that and deal with the AR later.

*Sorry for the hijack, but I didn't want to start another GAS PORT thread...

[rufracer]

I have a m1s 16" upper with a jp adj gas block on a cavalry arms lower, which has a rifle length buffer tube, and it works well with all supersonic loads ranging from 145gr w/18grh110 to 200gr w/17gr 1680, and subsonic loads 200gr w/12gr 2015. and 10gr 1680. The jp gas block works fine, if you get one, put a little teflon tape on the adjustment screw to keep it from backing out.

[grey2112]

Does anyone have the measured length of a pistol length gas tube for an AR? I need to cut down a mid-length to 7/8" less than a pistol length but need to know the length of the pistol length first before knocking another 7/8" off it.

[tp555]

Length is 6.7".You can cut down 3/4" and install to see how much slack you have.BC should not touch the tube and you can have 3/16" extra space.I once made barrels for a guy that was 3/16" farther away from the stock location.

[grey2112]

Thanks, TP - I had to drill out the hole in the gas block on both barrels to get the tubes to fit - VERY tight fit and hopefully I got them deep enough - will know soon when I test them out.

[tp555]

Shouldn't have to drill the blocks.They have a good no slop fit .I test with 2 gas tubes.Your gas tube would be the problem and could be too big.Gas tube is .180" dia.If you drilled it you will have gas leaks.A # 15 reamer is what I use for that hole.