I saw mentioned in another thread that you should get a 1/9 as the fastest twist for running a 22 conversion. I'm looking at building a 7.5" pistol and the barrel that I found is 1/7 and I'm thinking maybe I'd just use a 22 kit in this gun. I want it to be able to shoot 5.56 also, so don't say get a dedicated upper. I just think I'd use it a lot more for shooting varmints around the house, probably 20 yards maximum distance.

Accuracy in the 1/7 twist is ok. Can 5 rounds be  grouped in the size of  a nickel, no.  Can a 2 liter soda bottle be hit at 50 or more yards, yes. 20 yards should be no problem.

My personal experience:

1.  1-7 twist with an adapter yields 1.5-2" groups at 25yds.  No noticeable difference with 1-9.  

2.  10.5 & 7" barrels make my conversion a lot more picky on ammo compared to 16+.  

3.  I like CCI mini-mag 40gr.  Best accuracy-consistency-reliability for the $$

Notes:  Not much luck with bulk pack, Win M22, win 555, fed 500, or federal auto match.  Accuracy and reliability suffered greatly.  My CMMG dedicated 22 with 1-16 barrel is a little (maybe 30-40% more reliable) but much more accurate.  Easily <1" at 25 yards.

I run a conversion in a 1/7 barrel for Steel Challenge. I've not had any issues hitting the steel.  

Does the velocity of the ammo used in the 1/7 twist barrels make a difference in accuracy?

I own a old school 1/12 , several Maine built Bushmaster 1/9s , a stainless Rock River service rifle 1/8, and a stainless Stag 1/8. I run conversions in them all and the Rock River is most accurate by a bit and the rest all about the same .

Not sure how a 1/7 will do , especially a short barrel?

Clean after 5.56 with a good copper solvent for best results and accuracy will be quite a bit better with CCI STD , wolf match or other standard velocity types over any high velocity I have tried , even the better stuff like CCI mini mags .
Most of the bulk pac high velocity is pretty grim for accuracy.
Standard velocity is going to be fussy untill the conversion unit is broke in and smooth.
I have found the conversions work better when lubed with silicone or some type of "dry" lube over a oil lube.


Like I said , no direct with short 1/7 guns .
I expect for chasing around critters in the backyard it will do fine . If you are talking about smacking a crow at the far end of a field , nope ,you won't be happy