New build buffer and gas block question

[Bill257]

[LRRPF52]

Welcome aboard. It depends on what gas system length and port diameter you're getting with the 18". PF uses an intermediate length gas on the 18" supplied with the custom gas tube length for that, so I suspect a carbine or H2 buffer will work best, depending on the load range. If shooting 123gr and higher, I would stick with the H2. You will not need adjustable gas with the way that Intermediate GSL and port is set up.

I personally use H2 in 16" and 18" MLGS with .076 and .078 ports, which eject correctly at a 3:30 clock position.

For your gas block, make sure it's steel, and a low profile unit with .750" journal will do well, properly aligned. I would seal the gas system up front, as that will give you optimum gas delivery back into the Stoner internal expansion system.

Measure your gas port locations and know exactly how to endure Center to Center alignment of the ports. After torquing on the barrel nut (and a list of other thinsg) I test fit, then seal the block with Red Loc tite. I also seal the gas tube into the gas block. I just checked two 18" builds that I've done while we were up hunting in the mountains, and there was zero gas leakage from around the gas blocks or gas tubes. Both guns run like tops, no malfs to date in either.

Aligning the gas tube is also critical for longevity of the gas system, as any clipping of the tube will wear it away until gas leakage starts to cause short-stroking, and I have seen that happen, especially on longer gas system lengths shot in high volume.

I also bed the barrel to the upper, after ensuring a square receiver face with a lapping tool. Before I do that, I de-edge, blend, and polish the feed ramps to the upper if the chamber passes a cartridge fit test.

[Bill257]

Thanks LRRPF. I will get a H2 on order. I am familiar with aligning the gas port and tube and tightening in the barrel. But, I have not previously used locktite on the gas block or tube - I will be sure the front end is sealed up. Agree with lapping the upper, cleaning up any areas that need polishing on the chamber end of the barrel, and bedding the barrel. Much easier to take those small steps when it's apart the first time rather than troubleshooting or wondering if accuracy would be better if I saved some time during assembly.
Plan is to shoot factory 123 gr ammo for brass. If that works out, it can stay on a diet of hand loads with similar weigh bullets.
Still a few weeks out on the barrel so I have time to prep the upper.

[jim_bob]

LRRPF52,

By sealing the fron of the gas block do you mean putting a bead around the front where it meets the barrel after it is on the barrel? (Like caulk?)

[LRRPF52]

LRRPF52,

By sealing the fron of the gas block do you mean putting a bead around the front where it meets the barrel after it is on the barrel? (Like caulk?)

After I measure and test-fit the block, troubleshoot the gas circuit, I note the location and record that measurement (longitudinal/rear to front distances from barrel shoulder).

I slide the block off, then apply Red Loc tite 271 around the journal up front so the gas block will smear it to the rear. I make a ring leaving a space for the gas port so none gets in it, but put a little behind the gas port so there is a full circumferential application of the adhesive.

I then seat the gas block over the journal to the correct location previously measured so that I have center-to-center alignment of the ports, checking for TDC.

Once that sets up, I put Blue Loc-tite on the gas tube where it goes into the block, behind the tube's port, and install the tube. You can also dab LT on the back of the tube and block once the tube is installed to seal it there. I get no leakage this way.

[jim_bob]

Thank you very much for the clarification and instructions, I greatly appreciate it!