Poor groups with two Grendel barrels.

[Allen Roberts]

[Lemonaid]

AR, give the Sierra 120's a try (120 match king and 120 pro hunter). Even my BCA barrel would group less than 1 moa with these.

[grayfox]

Do you have a chrony so you can track some MV's? wide spreading MV ranges means the load isn't a good tune for your barrel.
My 20" BA shoots the 123 sst custom factory load, and the Federal 90 TNT well (1" or less), the Hdy Black, not so well.

[BlakeTX]

[mdram]

true the receiver face, see if the helps, maybe even bed the extension if its loose

[sundowner]

Did you get matching bolts . my 18" sanders put them in the same hole at 25 yards and cloverleafs then at 100 yards with their bolt .

[Klem]

Did you get matching bolts . my 18" sanders put them in the same hole at 25 yards and cloverleafs then at 100 yards with their bolt .

That's amazing precision for an AR barrel and rifle. I bet you are pleased with 0.26MOA.

[Allen Roberts]

I am breaking the gun down and have another barrel to try. My gas tube has a lot of play and wobble. Does that mean anything?

[sundowner]

That's amazing precision for an AR barrel and rifle. I bet you are pleased with 0.26MOA.

I love that barrel , replaced a BCA 18" barrel that had at it's best a 6" plus groups .

[sundowner]

I am breaking the gun down and have another barrel to try. My gas tube has a lot of play and wobble. Does that mean anything?

How tight is your gas block .

[Allen Roberts]

Thanks for your input. I am trying to trace accuracy problems on two barrels using the same upper/lower build. Aero precision upper, Anderson lower, nickel bcg, 2-stage RR trigger etc. Reviewing the situation 1) gas block / both barrels dimpled, block itself firm, but block/ tube slack and a lot of play on the receiver end.2) These are 20 inch rifle gas setups, but they would short stroke using rifle length springs. When I relaced the rifle length spring with a carbine length sling, short stroke problem was instantly solved. Any suspect area here? 3) cheap compensator w/ linear noise hood used on both barrels. Any suspect here? Same different ammo, maybe some improvement. I realize I may be the constant suspect culprit creating poor groups. I want to try to find that out.

[grayfox]

Is your stock a rifle length stock or carbine, as in adjustable length or etc? If rifle (A2-ish), then first thing, do not use that carbine spring in your rifle length stock. I don't care if it works (for now), it's bad juju safety wise (unless you have one of those "carbine stock inserts" in the tube as well that shortens the stoke).

The compensator is probably not an issue.

You say there is wobble in the gas block to tube fit-up, I wonder if that tube is even pinned? check that out, kind of a long shot but easy to verify. My probable culprits, losing gas or gas port too small.
A properly made gas block will fit tightly onto the GB journal of the barrel, no wobble, just barely slide on.

Case in point on the gas port. I have 2, 223 wylde BA barrels 18" RLGS, shoot really great but little to no lock back and definitely short-stroking. Near as I could measure their port holes they were the std BA diameter of 0.09375. The IMI 77 gr would cycle fine but virtually nothing else.
So after doing lots of search on the web for BA barrels it comes up that enlarging the port to ~0.100-ish solves this... ie, more gas pressure allowed into the DI cycle system. So I ordered a set of wire-gage drill bits and gradually opened the port to 0.1015 -- result, everything now cycles great. Federal 69 & 77 SMKs, cheap AE 193's, 69 gr Black Hills, IMI, Hdy black 75, everything I shot.
So if everything in the build checks out maybe look at enlarging the gas port. One nice thing about that is if you get 'way too large an adjustable GB can mitigate it.
Need to be careful however on drilling it so as to not mar the other side inner surface/land/groove. I put a cheap aluminum cleaning rod inside so I could hit that but not go too deep and hurt the barrel. Do this even if you have a drill press.

[grayfox]

Footnote to add: the gas tube will and should wiggle at the receiver end, allows for mate-up to the gas key during cycling.
Once you get the rifle to cycle completely and well, then it would be time to look for accurate loads.

[Allen Roberts]

[A5BLASTER]

Ok slow down and stop I mean stop lock the parking break sir.

Take us a pic of your buffer tube and stock. And don't do anything else until you post it here and we reply.

Because from what you just posted you have all kinds of wrong going on with your stock/buffer system and you don't know what's the difference between carbine and rifle length.