22LR conversion = scattergun?

[JGSFAB]

Okay the original CMMG conversion kit shot like OK , 4in groups at 30yrds. So I decided to add a 16in dedicated barrel to it expecting to pick it up some. 6in groups at 30yrds
Had to get out a 4ft pattern board to even see the hits. It this all I can expect? A factory 10/22 crushes it. At least the last 10rounds I held zero to see if it grouped at all. Was hoping to hunt squeaks with it, 10/22 it is.

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[eldbillbo]

That's not normal out of a dedicated barrel The 4" group out of 1/7 twist barrel would see 4" groups. It looks like something else is going on. are you shooting with or without an optic? maybe a loose scope mount or broken reticle. if open sights maybe loose sights. maybe a batch of bad or really old improperly stored ammo.

 

[JGSFAB]

That's not normal out of a dedicated barrel The 4" group out of 1/7 twist barrel would see 4" groups. It looks like something else is going on. are you shooting with or without an optic? maybe a loose scope mount or broken reticle. if open sights maybe loose sights. maybe a batch of bad or really old improperly stored ammo.

Ammo is old but same ran thru the 10/22 yields good results. 40gn Winchester white box. Swapped scopes now has a known good 3-9 Leopold.
Everything is tight. I'll check the barrel nut/barrel to upper connection. Shooting from a good solid bench off a bipod.

 

[eldbillbo]

look at the crown on the muzzle and see if it was damaged and Check those things and maybe just to be sure run some fresh ammo from another brand (highly doubt that is the issue but worth checking before making the phone call. if none of those things work I would contact CMMG because that is not normal.

Also and you probably know this but just in case as I don't know your experience of shooting an AR style rifle make sure there is no tension on the barrel I have seen guys at the range supporting their rifle on a rest by the barrel when it should be resting on the handguard this will give cause a bad group although probably not that bad.

 

[RX-79G]

Try some Aguila subsonic?

 

[JGSFAB]

Good call on the crown , it doesn't have one ... dafuq

 

[RX-79G]

Good call on the crown , it doesn't have one ... dafuq

View attachment 1450506

I wouldn't say that is not crowned. But it isn't recessed, which might not be necessary since it is intended to have a flash hider.

 

[bcp]

That looks like it was crowned with a chattering countersink or large drill bit.

I. would chuck a round head screw in a drill. Apply some valve grinding compound and spin it against the muzzle until you have a nice, even crown.

Bruce

 

[Hueco]

What's the twist on your dedicated barrel?

 

[JGSFAB]

1:16 twist. I know a guy who has a large selection of precision crowning tools

 

[msgriff]

A chamfering reamer might be useful.

 

[Hueco]

I'm hesitant to believe that even a crown carved with an axe would have THAT much effect at 30 yards…something is wonky. Have you chambered a round then popped it out? Is the lead getting messed up on chambering? Any chance the bore or rifling is cut off spec?

 

[RX-79G]

I would look at the barrel nut and sight mount(s). A smoothbore will group better than that.

 

[msgriff]

If you wanted to check for a loose barrel, this is something that I picked up in a backwards sort of way regarding barrel seating and movement in relation to the upper. This is similar to what brought about barrel shimming and bedding many years ago.
Use aerosol CLP, or even WD-40, with the straw. Hold the straw tight to the seam between the barrel extension and the barrel socket inside the upper, and spray around the circumference. Wipe off the excess, clamp down the upper so you can still see inside, then move the barrel around. The CLP will ooze out if there is movement.
I'm not suggesting that bedding is required, but there are other issues that can cause excessive movement, which could be the cause of your target pattern. The first couple minutes of this vid might help explain it.

 

[eldbillbo]

It muzzle looks dirty I don't really see any nicks or dents deep enough to cause that kind of inaccuracy. I wouldn't touch the crown without consulting with CMMG as it might void any kind of warranty.

 

[JGSFAB]

I have my choice of JGS Precision Tool Mfg form tools , any crown I like. They all work with a basic tap handle for hand cutting.
Or we sell a T handle but that's mainly for assembled actions with hand headspacing a chamber.

 

[JGSFAB]

Its not a CMMG barrel and I doubt the CMMG bolt is causing inaccuracy.

 

[2Wheels4Ever]

My dedicated conversion shoots a 3-4 inch group at 50y. Not as good as my 10/22, but okay for what it is. There's more at play here than just crowning. 4ft group at 30 yards?! If the bullets aren't tumbling, then something has to be loose.

 

[JGSFAB]

That target was me trying to sight it in. I was out of time to toss up another paper to get some just groups.
I'd say its 6in at 30.
Nice to hear its not as good as a 10/22, I don't see how it could be even with a great barrel.
Gonna see what busing fits the bore. Barrel isn't loose.

 

[quneur]

@6 min mark. He shot targets at 50 yards. The accuracy is about average shown for the CMMG conversion kit.

I suspect its either or combination of these:
1. loose tolerance of the 22LR (5,7mm - 5.73mm dia - taken from wikipedia)
2. barrel twist rates. (22LR typically 1:16 - 1:20 vs 223/556 1:7 - 1:9)
3. barrel length - AR pistol vs AR rifle. As an example, shooting out of a 16" barrel with 1:8 twist, the projectile will spin twice as much. If out of a 8" barrel with 1:8 twist, it will spin once. Is that enough to stabilize? Idk