CMMG 22lr Kit and Short 556 Barrels

[FRKN9]

Considering a dedicated 22lr AR upper "pistol blaster" project using the CMMG 22lr conversion kit and a 4.5" 556 barrel.  I know there are a whole lot of reasons it would be better to have an actual 22lr barrel, thing is they're hard to get and really expensive compared to 556 barrels.  I'm not going for sub MOA precision here however getting around 2" groups at 50 yards and in would be the goal.  With the way the CMMG kit fake 556 adapter works for 22lr there's the jump to the bore and that leaves about 2.5" to 3" of actual usable barrel.  I'm not sure if this will work well or not.  If I get 6" groups at 25 yards that would qualify as failure.  I've used the 22lr kit in a 7.5" barrel and had very good results out to 50 yards but with a 3" (40%) shorter barrel I'm just not sure it will work well.  If anyone has experience with the CMMG 22lr conversion kit in really short 223/556 barrels I'd appreciate anything you could tell me. 

[MuffintopMarksman]

I’ve only used that kit on a 10.5” barrel but I would suspect decent accuracy in that 4.5”as most 22lr pistols can delivery good groups with such barrel lengths. I’ve had a couple Ruger Mk series do just fine at 25yds as the bullet has plenty of barrel to work with (it’s been a few years but 2” groups could be reached on my better days). The greater stability of a braced gun would likely do fine. My 10.5” could drill a nice 3” group at fifty which is not bad given the bullet size difference between the two cartridges.

[OpenshooterMclass4lyfe]

I haven’t shot them out or anything that short but from my experience it should be fine for what your trying to do 

[FRKN9]

I've decided against the 5.56 barrel with a 22lr converter for this.  It may work fine however an actual 22lr barrel would work significantly better.  I'll either wait out the CMMG 22lr barrel drought or buy once / cry once with a custom 22lr Beyer barrel.