Gas Block to Barrel "Step" Gap

[freedom-lover]

I believe I read on here somewhere when installing the gas block it should be shoved up against the adjacent barrel "step". What should the appropriate gap be, 0.010", 0.030"?

[nicoroshi]

Ar or ak?

[FMJBT]

On an AR, it's going to be dependant on the gas port location. Best way is to measure how far the port is located away from the rear step as well as how far the port inside the gas block is from it's rear face. The difference in those measurements will be the amount of gap you need between the gas block and shoulder/step of the barrel. The port in the gas block is typically oversized when compared to the port in the barrel, so there is a bit of wiggle room for error. Most of the builds I've done end up with about 1/16" gap behind the gas block.

[finyllw]

You need to measure were the hole is on the barrel (from the step) then measure the hole in the gas block from the edge were it touches the barrel step. They need to be very close to the same measurements.

[freedom-lover]

AR, sorry. There was already a single dimple on the bottom of the barrel, but when tightening the set screw, the dimple size allows quite a bit of movement of the gas block along the axis of the barrel. So, it could be anywhere from up against the barrel step (0" gap) to perhaps 0.050" gap.
So, what you are saying is the two holes should be as concentric as possible? Isn't the gas block hole bigger than the barrel hole?

[FMJBT]

AR, sorry. There was already a single dimple on the bottom of the barrel, but when tightening the set screw, the dimple size allows quite a bit of movement of the gas block along the axis of the barrel. So, it could be anywhere from up against the barrel step (0" gap) to perhaps 0.050" gap.
So, what you are saying is the two holes should be as concentric as possible? Isn't the gas block hole bigger than the barrel hole?

The gas block hole is typically a bit larger than the gas port in the barrel, unless you are running an odd gas system configuration like a dissipator that needs a very large gas port. Barrels that are dimpled make alignment kind of a non issue as long as the dimple lines up with the gas port. The set screw hole on the gas block itself should align with the hole for the gas port at the top of the block. If machined correctly, the setup is self aligning and all you really need to do is torque down the screw in the dimpled hole first before tightening the second set screw over the non dimpled barrel surface.

[freedom-lover]

The gas block hole is typically a bit larger than the gas port in the barrel, unless you are running an odd gas system configuration like a dissipator that needs a very large gas port. Barrels that are dimpled make alignment kind of a non issue as long as the dimple lines up with the gas port. The set screw hole on the gas block itself should align with the hole for the gas port at the top of the block. If machined correctly, the setup is self aligning and all you really need to do is torque down the screw in the dimpled hole first before tightening the second set screw over the non dimpled barrel surface.

It is a YHM gas block (0.750") going on a Bravo Co barrel. The dimple lines up with the gas hole, and on the gas block the set screw lines up with the hole. What I am saying is that when tightening down the set screw there still is a little bit of wiggle room (before the set screw is fully tightened) that allows one to move the gas block 1/32" or so back and forth along the axis of the barrel. On the rearward extreme travel it will hit the step. On the forward extreme travel, a gap of 0.050" or so is possible.

[FMJBT]

1/32" either way should be within the area that the hole in the gas block covers. If you want it to be perfectly centered, you'll have to take the measurements for the port locations and line them up manually and then tighten the non dimpled screw first. With higher quality parts like BCM and YHM, I'd just torque it down centered on the dimple and run with it.

[ar15barrels]

It is a YHM gas block (0.750") going on a Bravo Co barrel.

You want a 0.025" gap between the rear edge of the gas block and the step on the barrel with those parts.

[cbt engr]

remember that the gap is for the handguard cap