I just built a .22LR SBR upper for my AR. I used a CMMG 1:16 9" bbl, their stainless .22 kit, an Anderson upper, and a UTG 7" free float bbl. It looks really sharp and is light and handy. But it won't hold a group at all. Last week I tried it with an old red dot I had lying around and got the same results as this week with a new mount and new Leupold scope.

I tried 3 different types of ammo, 2 different mags, and with my Paradigm suppressor, with A2 flash hider, and bare muzzle. All groups acted about the same. First shot, 4-6" or more higher, the subsequent shots lower but in a 4-6" pattern. Can't even really figure out a center for the so-called group.

Reliability was quite good at least.

Where do I start troubleshooting this? I'm thinking to remove and re-torque the bbl but nothing is noticeably loose. I'll call CMMG on Monday to see what they say, but this is always a good place for advice.

So, what should I do to troubleshoot? Ejected live rounds don't show any undo wear or dinging from being chambered.

Thanks,

Bitter Bastard

I would start with a good cleaning of the stainless barrel with a brass bore brush... add a plug to hold buffer spring tension on the conversion unit to help control  head space.... CCI mini mags shoot fairly well in all of my rimfires...

What distance are the 4"-6" groups at?

Did you try standard velocity ammo? CCI STD , Wolf or federal target or the like

In my conversions the first hand cycled round goes into the dirt , second auto loaded round starts the work on paper.

Take a good close look at the crown (muzzle) of the barrel with a strong light and a glass . smallest nick or burr will wreck things

Shooting was at 25 yards, bbl was new last week with the crappy scope.  Shot 50-60 rounds both last week and this week.  Bbl is parkerized, conversion is stainless.  I gave the bbl a light cleaning before the first shooting session but not between the two.  I just not gave it a good cleaning and it looks fine, including the crown.

I tried CCI and Mag Tech subsonic and Remington Thunderbolt supersonic ammo.   All 3 functioned fine but produced the same crappy groups, or lack of groups.

Anything else I should look at?


Bitter Bastard

Look for a dinged crown maybe.  

I'd also shoot some, and eject a live round from the chamber.  Inspect that.  How bad is it dinged on the way into the chamber.  

My CMMG groups well.  It's my Nordic that never shot good and shoots like yours.

Is the problem with your aiming device? (sights or scope).  Also, make sure barrel is tightened properly. Have had issues like this and it turned out to be either the optic or a loose barrel. Sometimes you have seem to have the barrel nut tightened properly but still have a barrel that is slightly loose.

Another problem is feed ramp/bolt damage to the nose of your bullets.  I have seen guns that would hit the nose of the bullet as it was fed making a big dent on one side. This really caused the accuracy to suffer. Just another thing to think about.

It should of course shoot way better than this

I am thinking the relationship between the sights/optics and bore . in other words , loose scope,loose barrel or something

No matter how badly the bullet is getting bashed when chambering I can't see it having a huge effect on a slower rimfire round at 25 yards

This is the .22 adapter that fits into a standard 5.56 barrel and replaces the existing BCG?  What if you remove the adapter and shoot some 5.56 through it?  Might eliminate a bad crown, optics, barrel torque, etc. as potential problems.

Plus it's easy to do.  

Can you post a link to the Stainless kit you bought ?

Also ... my TACCOM upper really took about 300 rds to " season" the barrel enough.

Now it groups great... when brand new groups were 3-4 inches at 50yds.

It loves the GEMTECH 42gr subsonic.

Thanks for the suggestions so far.  I called CMMG and they sent a shipping label to return it.  They even wanted the whole upper, including (at my option) the scope to test with, even though it is only their bbl and bolt.  Great customer service so far.

I was hesitant to send it back, so I bought a receiver block and torque wrench (I borrowed those to assemble it), and removed and re-installed the bbl tonight.  It is *maybe* shooting slightly better now but not really.  So now that I'm pretty certain it's not a dumb mistake I made putting it together, I'll get it sent back in the next day or two, I just need to find a box.

The best group I had tonight by far was with CCI standard velocity and the Paradigm.  It was about 1.5" at 25 yards.  Most other groups were still 4-6".  Heck, I have a 25 year old 10/22 and S&W .22 pistol that can beat that all day long.

But kudos to CMMG for stepping up the plate so far.  I'm curious to know what they find.  I'll update when I hear back.

To re-iterate, this is a 1:16 twist bbl (parkerized or whatever) and a stainless bolt group and bbl collar.


Bitter Bastard