Gas system issue. I need some help

I have an 18" Grendel upper that I put together using an AA barrel. The barrel is bedded with 242. Barrel nut is torqued to 70 ft lbs.

When shot completely assembled, the gun shoots 1-1/2" to 1-3/4" with handloads. If I shoot it with the gas block and tube removed, venting the gas out of the port, the gun shoots 3/4" to 1". I am going to hunt with the rifle so the 3/4" to 1" is fine, I just can't get there with the block and tube installed.

Alignment of the gas tube is fine. I'm using an EGW aluminum gas block. The gas block has not been "bedded" yet.

I have tried alot of different component combinations with out any luck.


Ideas????

Any help would be GREATLY appreciated!!!!!!!

Thanks,
Trilogymac

I have an 18" Grendel upper that I put together using an AA barrel. The barrel is bedded with 242. Barrel nut is torqued to 70 ft lbs.

When shot completely assembled, the gun shoots 1-1/2" to 1-3/4" with handloads. If I shoot it with the gas block and tube removed, venting the gas out of the port, the gun shoots 3/4" to 1". I am going to hunt with the rifle so the 3/4" to 1" is fine, I just can't get there with the block and tube installed.

Alignment of the gas tube is fine. I'm using an EGW aluminum gas block. The gas block has not been "bedded" yet.

I have tried alot of different component combinations with out any luck.


Ideas????

Any help would be GREATLY appreciated!!!!!!!

Thanks,
Trilogymac
Did you try dropping the powder charge? Did you chrono with and w/o the block?

That should be a blast to shoot, pun intended, without a gas block. Glane had a good question and the only thing I can add at this moment if it's not a velocity change issue, I'd say maybe the gas block is disrupting the barrel's harmonic vibrations.

Joe

That should be a blast to shoot, pun intended, without a gas block. Glane had a good question and the only thing I can add at this moment if it's not a velocity change issue, I'd say maybe the gas block is disrupting the barrel's harmonic vibrations.

Joe
Good point Joe, that would be about all I could come up with if not velocity changes. I wonder if he has access to a different gas block. Is that EGW adjustable? I doubt not having the GB loctited in would change things that much but I guess stranger things have happened. I guess I'd ask him what the groups are doing? Are they opening up just generally speaking or stringing vertically or horizontally?

I looked at that block on the web and it appeared to be a clamp type. I would think it clamps very tight and it's made of aluminum so it shouldn't be that heavy. Can't see it changing the barrel vibrations a lot being in the middle of the barrel.

Joe

I've tried up down in and out for loads. Have not chrono'ed it but have covered the spectrum with different components. I have a JP adj gas block
to try. That is my next attempt.

Any and all help appreciated!!

Trilogymac

I looked at that block on the web and it appeared to be a clamp type. I would think it clamps very tight and it's made of aluminum so it shouldn't be that heavy. Can't see it changing the barrel vibrations a lot being in the middle of the barrel.

Joe

I tend to agree with you on that. My best guess is a velocity problem. Now I'm not sure if that's with different bullets or not though. He really didn't elaborate besides saying he'd tried different combo's. I'd be more suspicious if it were several different types of bullets and/or powders, OAL etc.

I've tried up down in and out for loads. Have not chrono'ed it but have covered the spectrum with different components. I have a JP adj gas block
to try. That is my next attempt.

Any and all help appreciated!!

Trilogymac
What are your groups doing? Stringing or just getting bigger? Is that with different bullets also?

I've tried up down in and out for loads. Have not chrono'ed it but have covered the spectrum with different components. I have a JP adj gas block
to try. That is my next attempt.

Any and all help appreciated!!

Trilogymac
I've got a JP adj on my 18" and I like it better than the PRI it came with. It just feels smoother when it cycles with the JP vs the fixed orifice. It did take a few rounds to carbon up the set screw for it to seal off and cycle right so you might find the same thing happen. After I got it set, I screwed it in to count how far out from bottom it was. I then put some purple loctite on the set screw. it has an 8-32 set screw I believe. They could've gone with an 8-40 and tightened up the threads to help seal better.

I've got a JP adj on my 18" and I like it better than the PRI it came with. It just feels smoother when it cycles with the JP vs the fixed orifice. It did take a few rounds to carbon up the set screw for it to seal off and cycle right so you might find the same thing happen. After I got it set, I screwed it in to count how far out from bottom it was. I then put some purple loctite on the set screw. it has an 8-32 set screw I believe. They could've gone with an 8-40 and tightened up the threads to help seal better.

I'll bet it's a 10 32, that's what the adjustable gas tube valves are.

My PRI with the adjustable gas valve on the tube cycles just wonderfully.

Joe

I'll bet it's a 10 32, that's what the adjustable gas tube valves are.

My PRI with the adjustable gas valve on the tube cycles just wonderfully.

Joe
Just double checked it. Its 8-32 on this block at least. I liked the PRI block that came with the bbl but I wanted adjustable and to have a top rail for my front folding sight. I think a 8-36 or 8-40 tight thread would be better than this 8-32 with the sealing issue. They might not be able to get a 10-32 or 10-40 in there, it would be close in the area its tapped.

[QUOTE=trilogymac The barrel is bedded with 242.

I'm using an EGW aluminum gas block. The gas block has not been "bedded" yet.

Trilogymac[/QUOTE]


Describe the barrel bedding in detail. Actually, I would like to know the entire setup in detail. I'm using three of the .938-.940 EGW blocks on various builds, IMHO no need to bed them.

Every reloader should have a decent chronograph, it can be an invaluable aid. If you had a chrono you could match velocity in an attempt to duplicate the fundamental barrel node. I've never given it any detailed analysis, but on the surface I think a gas gun has a fundamental and at least two harmonic barrel vibration nodes.

For giggles, move the gas block forward about .090 or whatever it takes to block the gas port. I'm curious if there's an accuracy difference between blocked and venting.

mike

[QUOTE=trilogymac The barrel is bedded with 242.

I'm using an EGW aluminum gas block. The gas block has not been "bedded" yet.

Trilogymac


Describe the barrel bedding in detail. Actually, I would like to know the entire setup in detail. I'm using three of the .938-.940 EGW blocks on various builds, IMHO no need to bed them.

Every reloader should have a decent chronograph, it can be an invaluable aid. If you had a chrono you could match velocity in an attempt to duplicate the fundamental barrel node. I've never given it any detailed analysis, but on the surface I think a gas gun has a fundamental and at least two harmonic barrel vibration nodes.

For giggles, move the gas block forward about .090 or whatever it takes to block the gas port. I'm curious if there's an accuracy difference between blocked and venting.

mike[/QUOTE]

That's a good idea to check the harmonics theory. Even cover it 50%. I didn't bed my block either. That is on so tight I don't think it's needed. I guess it might provide some cushion but we're really getting over kill at that point.

Trilogy, check your bullet seating depth!

I've been reloading for my Grendel for 2 years now, and I've found that the biggest difference in my groups has been how close in to the lands my bullets are seated. My most accurate loads, 1/2 or less MOA consistent, are when the bullets are right up just touching the lands. The tough part is, a lot of the smaller bullets won't make magazine length when seated this way (for my rifle/chamber/throat). (19.5" Hunter barrel)

REMEMBER though, safety first: We must use a reduced charge when close to or touching lands! Always check loads with a good gage, chrono them, make sure cases are not too long!