10-08-2015, 03:08 AM
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.
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.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com