This was a bit of a saga. The bolt assy was originally used as a conversion in a 7.5" pistol and was well broken in.

Immediately there was a problem with the barrel. With most all ammunition, groups at 25 yards hovered at around 3-4" inches. A lot of experimentation with barrel nuts, optics, and several different types of ammo netted no difference. CMMG shipped a new collar which made little if any difference. Eventually they replaced the barrel.

The results. L to R: Original barrel, replacement barrel, and S&W 15-22 rifle for comparison.
20170616_004441 by Slick_Rick77, on Flickr

Representative groups range from 2.5," to 1.5," to 3/4," respectively.

The final results with the replacement barrel show it not to be a tack driver...but acceptable.

The little gun has spawned a few configurations.

There is a micro pistol with an alloy barrel extender.
20170603_082756 by Slick_Rick77, on Flickr

Suppressed.
20170604_190231 by Slick_Rick77, on Flickr

Suppressed SBR.
20170510_084447 by Slick_Rick77, on Flickr

...and finally the forend was drilled and tapped for a sling stud and a bipod equipped mini-sniper was born.
20170608_164820(0) (1) by Slick_Rick77, on Flickr

The kid having a go with it:
20170608_180140(0) by Slick_Rick77, on Flickr

Some live action:
https://www.youtube.com/watch?v=F_oEjnulRBA

The parts:
• CMMG bolt assy, barrel and collar
• Superstition Precision alloy barrel extension
• Anderson upper/lower
• Unknown takeoff mil spec trigger/hammer
• Wolff reduced power trigger and disconnector springs
• Generic/no name LPK
• Lone Star Ordnance A2 stowaway grip
• UTG 30mm red/green dot
• Ergo rail section
• Strike Industries Cobra AFG
• Fieldsport free float tubes
• Slipstream Precision 22lr receiver plug
• EMA tactical one point sling
• KNS anti-rotation pins

The SBR lower is all Anderson with a Wolff reduced power trigger and disconnector spring set with KNS pins and an AR-Stoner stock assy.

It's nothing too fancy or exciting, but it is a lot of fun and is quick becoming my most used gun.

I like it a lot. I'd prefer a VFG, but don't feel the tax stamp would be worth the expense.

With some pressure against the sling it's reasonably stable.

Your AR pistol is bad-ass. Re-barreling it in 5.56 or 300BO seems like a good option.

Already having a bolt assy and some spare parts made it a relatively inexpensive proposition to put a new gun together.

The handguards just thread off on a common barrel nut.

As far as accuracy goes, make sure you have a crown on the cmmg barrel, they released some 4.5 barrels without them. I have played with several configurations of the 4.5 barrels, and what i have found to throw off accuracy like that; are barrel extensions and/or suppressors. I had fake gemtech, just to clear handguard and was getting crappy groupings too. I also had extension from silencerco that would throw off groupings. I took all that off. It improved at 50 yards I would say 1.5 groupings.  l

Both had decent crowns. The first barrel had a land that appeared a bit nondistinct.

At worst if the threads aren't concentric there should be some zero shift, but not inaccuracy.

It depends on turbulent flow disrupting the bullet, which would cause accuracy issues. What is the diameter of your extension?

The I.D. 0.438."

The groups were fired suppressed, and the suppressor has not affected the accuracy of other guns I've used it on.

Bloop tubes have been commonly used on 22lr competition guns for some time.