gas tube variants
am building an upper with an Alexander Arms 16" barrel chambered 6.5mm Grendel.
surprise, the gas port's position is somewhere between the location for a full length rifle barrel of my Colt Sporter and that for the Bushmaster 16" barrel I have on a CAR.
I need a gas tube whose length is between these two, don't have one. A gunbroker seller lists a 'midlength' gas tube.
Are there standard nonstandard lengths of this tube?
Also, am using a one-rail gas block to connect this tube to the barrel. is there any part that must go between the gas port and the tube, or do I just clamp the gas block to the barrel (two setscrews) and pin in the gas tube?
Yr collective wisdom would be appreciated.
I think the mid length is the best compromise for the 16" barrel. I have an armalite 16" mid length and its as easy to shoot open sights as my full length A2, compared to my CAR upper. Eye balling my gas tube it looks like its about 11 3/4" or a little less, and the gas port is about 10" from the back of the barrel extension if that helps. Unless its a specialty item its probably the mid length setup. I have the same gas block setup on my bull barrel and you got it right. If its the 2 setscrew type thats all that holds it on. It should fit on snug so it doesn't leak gas. I used a block of oak to help drive the gas block into position. Make sure you test fire it before cranking down on the setscrews to keep them from wanting to return to where they were first set. My buddy puts locktite on the bottem half of the gas block (to keep it out of the gas port) for a little added security. I don't have anything mounted on my gas block rail so I didn't locktite it and I've had no issues with it.
My gas block is nominally .750" ID, the portion of the barrel around the gas port is nominally .750" OD. The block slips easily on the barrel, no gentle persuasion by tool was required.
This worries me a bit, but as you say, locktite it, that may hold it firmer. Don't want to shim it if that can be helped.
I see Rock River listing a midlength tube, in addition to gunbroker vendor listing. So they're out there. Thanks
if you can slide that block without much force, you will have a issue with gas leakage, unless you find one that fits better or use the locktite as stated above