09-16-2013, 10:01 PM
I have the JP gas blocks too and if all else fails, read the directions. (they come with the GB's) It says to leave the gap as LRRPF52 just said, I think it is .025. I measured the center of the gas port on the GB to the shoulder of the GB and use a feeler gauge between the barrel shoulder to get the exact measurement. Some times the .025 is not correct.
Also on set screw GB's, the one rear screw lines up with the gas hole in the block. Use that as the measurement and check the bottom of the barrel set screw dimple, they line up with the gas port in the barrel. Then no measuring for the set back, just line up the dimple to the set screw hole and tighten the front screw first.
anyhow, DIRECTIONS, I hate them too...
Also on set screw GB's, the one rear screw lines up with the gas hole in the block. Use that as the measurement and check the bottom of the barrel set screw dimple, they line up with the gas port in the barrel. Then no measuring for the set back, just line up the dimple to the set screw hole and tighten the front screw first.
anyhow, DIRECTIONS, I hate them too...