223/5.56 heavy bullet (> 55 gr.) start to become unstable about 80 yards in the 1:12 twist M16A1 barrel. They may not keyhole, but the accuracy does start to go south.
The Army used the M261 sub cal device to use 22 Rem Fire in the 'A1. With its 1:12 twist best accuracy was a 50 feet. It worked at 25 yards but the accuracy wasnt there.
There has always been a need for weapons training where outdoor ranges werent available and reduced loads for gallery shooting has been around since the days of 45-70 Model 1873s. Older military marksmanship and reloading manuals have references these gallery loads. The M261 was the latest attempt that I'm aware of.
I have tried to shoot a 100 yard reduced NRA high power match using the M261 without much success.
I havent tried to use the M261 & 22 RF in the 1:7 twist barrels, in the next few days I'll try it and see what happens.
M261 Sub Cal Device
This is my winning AK NG team at a trip to Nashville to compete with winning teams of other states, shooting the M261 at 50 ft.
This next is a test the Army conducted comparing the 1:12 and 1:7 twist barrels. It doesnt cover the 22 RF but gives an idea of what happens with different bullet weights.
Of course there are exceptions to every rule. It certainly doesn't hurt to try 22s in a AR to see where the accuracy in your rifle starts to go south.
I know in my 1:12 ARs this occurs between 60-80 yards but my 1:12 Rem. 700 BDL Var does group well at 100 yards using 62 gr Speer LE ammo. My 1:12 SP1 doesnt.