POI shift

[Robbie Wheaton Jr]

The gas adjustment screw on my gasblock backed out while shooting Sunday? As the screw backed out I noticed a huge POI shift. When the screw finally came all the way out the POI shifted over a foot @ 300yds. When I reinstalled the screw and re-zeroed at 100yds everything worked fine again. I never realized how much the POI could shift because of the gas adjustment screw. Has anyone ever shot a group then backed the screw out a turn shot another group? I need to do more testing but if the screw moving a little could cause a POI shift I will probably replace the adjustable gas block with a standard gas block.

[Charles Bond]

The gas adjustment screw on my gasblock backed out while shooting Sunday? As the screw backed out I noticed a huge POI shift. When the screw finally came all the way out the POI shifted over a foot @ 300yds. When I reinstalled the screw and re-zeroed at 100yds everything worked fine again. I never realized how much the POI could shift because of the gas adjustment screw. Has anyone ever shot a group then backed the screw out a turn shot another group? I need to do more testing but if the screw moving a little could cause a POI shift I will probably replace the adjustable gas block with a standard gas block.

It is always nice to get information such as this from folks like you who have have the ability and the time and the equipment to do this test. I can not wait for the results and I of course am counting down the days until the Ft. Benning Match.

[00bullitt]

Yep.....happened to me before. I was told I was crazy.....that impact would not change with a gas adjustment. I knew it was the reason. It makes sense to me that impact could change with adjustment.

[Sterling White]

It's makes sense that it would because of the pressure change.

[lefty556]

Makes perfect sense to me. If you minimize or shut off the gas port completely, the gas has to go somewhere. The only place it can go is out the muzzle. By minimizing or closing the gas port, you have increased the volume and pressure of the gas behind the projectile. That will affect velocity, which affects POI. It may also make a change to the barrel harmonics, which will affect POI.

[lynn jones]

i need to check my gas jp gas block. i haven't touched it, but all of a sudden i'm 6" high at 100yds.

lynn

[mpeltier]

The gas adjustment screw on my gasblock backed out while shooting Sunday? As the screw backed out I noticed a huge POI shift. When the screw finally came all the way out the POI shifted over a foot @ 300yds. When I reinstalled the screw and re-zeroed at 100yds everything worked fine again. I never realized how much the POI could shift because of the gas adjustment screw. Has anyone ever shot a group then backed the screw out a turn shot another group? I need to do more testing but if the screw moving a little could cause a POI shift I will probably replace the adjustable gas block with a standard gas block.

If you do more testing try it without the comp, then make adjustments to the gas block and see if POI changes with a bare bbl. What comp are you using anyway?

[Charles Bond]

It's makes sense that it would because of the pressure change.

And that does indeed seem to make sense and would make a lot of sense if the gas port were further down the barrel. The way I think about it is that by the time the projectile has any pressure change in the barrel due to a change in the gas block setting, the projectile has already exited the barrel. I have no science degree and can not afford Holiday Inn Express but if Robbie says it does, you can take it to the bank.

[Religious Shooter]

That's interesting.

1' @ 300 yards is 4" @ 100... that's a huge shift.

I'll go try it tommorow.

[Singlestack]

After mine shifted I opened it all the way and put locktite on it.

[dt1]

That's interesting.

1' @ 300 yards is 4" @ 100... that's a huge shift.

I'll go try it tommorow.

Are you sure about that?

[cold]

After mine shifted I opened it all the way and put locktite on it.

After mine came out at the last stage of the FNH USA match (went single shot, fun times :/ ), I got another screw from JP, and loctited that ITCH in place something fierce.

[Religious Shooter]

That's interesting.

1' @ 300 yards is 4" @ 100... that's a huge shift.

I'll go try it tommorow.

Are you sure about that?

Sure about what?

4 MOA = 3 x 4" = 12" = 1' @ 300 yards

[Religious Shooter]

I tried it. For 3 Gun I wouldn't worry about it.

I'm not quite 100% sure that it will "universally" cause a shift. For my uppers if I take out or fully screw in the screw the gun won't cycle. The cycling changes and the resulting follow-through can be different. It's like shooting the last round out of the magazine and the bolt locks back. That last round can open up the group. I also had to hand cycle the action for the extreme ends of adjustment.

I don't think one or two turns is going to do anything. If you are worried about it... just loctite the screw.

The range was fairly windy. If you like watching paint dry...