RattleAkAk Wrote:I have a 16" BA Hanson Midlength Gas 6.5 Grendel barrel that has always ran like a sewing machine since I got it. The rifle has gone through a rebuild and I replaced the pinned gas block that it came with, with a Geissele Super Gas Block. Took it to the range today and short stroke city, no lock back, refused to strip a fresh round from the mag etc. I swapped lowers, bolts, mags, ammo etc. to isolate the issue, its definitely being choked out. I am meticulous in my rifle building and am 100% confident that the gas block was aligned properly, gas tube installed correctly and not obscured. I broke the rifle down and compared the Geissele gas block with the BA Hanson one and the gas port on the Geissele is noticeably farther from the "shoulder" than the BA one. I have since reinstalled the BA Hanson gas block and will take it to the range ASAP. I just wanted to see if anyone else has had issues running a non BA Hanson gas block on these barrels. I have attached a crude illustration of what I observed, as I didn't write down the measurements I took with my calipers.
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If all things are equal it sounds like your gas block port and barrel gas port are not lined up. Some gas blocks are made to fit against the barrel shoulder and others to fit with the hand guard retainer. This is why gas block ports can be drilled differently.. In any case it is best to measure for proper port alignment. It is easy to get the measurement from the gas port to the barrel shoulder and the same for the inside gas block port to the outside of the gas block to get proper alignment. If the gas block port and barrel port are lined up and it continues to short stroke, then the barrel journal could be undersized for the new gas block or vise versa. The barrel journal and gas block needs a fairly tight fit to prevent gas leakage.. Leakage can occur with a different gas tube, the gas tube fit in the new gas block or the gas tube fit to the gas key..If your Geissele gas block is the screw type, I would recommend dimpling the barrel under the gas port for your set screw. SLR makes an excellent jig for dimpling the barrel for proper gas block alignment. You have to order the correct size for a standard .750 barrel journal or the .625 used in many pencil barrels.https://slrrifleworks.com/750-dimpling-jig/ If the new gas block uses a pin, then the pin channel in the barrel and gas block pin hole may be different. This can cause the gas ports to not align properly.. The best and sure way to verify port alignment is with a bore scope.