Always looking for a way to get more bang for the buck, I decided to try one of the .22 long-rifle conversion kits for our police AR-15 patrol rifles.
Got the kit, which is simply a drop-in replacement for the bolt-carrier group, and a new magazine, for $169. It very simply just dropped in, replacing the bolt-carrier group. The magazine has a couple of "bumps" molded in that can be filed down for a precise fit to individual guns, but as yet I haven't done that and the mag works just fine in several different rifles. It's a snug fit though.
For ammo I used CCI mini-mag 40 grain .22 long-rifle, a plated bullet.
The first impression from every shooter so far has been a huge grin! ;D Next is a realization that the rifle, fitted with this conversion kit, is both accurate and reliable. All our shooting so far has been at 50 yards and in, as appropriate. Accuracy appears to be on a par with that we're getting from 55 gr FMJ 5.56 ammo, and we haven't had to adjust the sights either.
What this means to me as a trainer is that I can get the guys about four times as much trigger time for the same amount of money. We can do the majority of our practice with inexpensive .22 long rifle ammo, then switch to the 5.56 mm ammo for qualification and a little more training where the muzzle blast of a full power cartridge is an important aspect of the training.
Marksmanship though - we're going for the .22's all the way. At this point I've got us three of the conversion kits, and am looking for three more. As a bonus, I was able to swap seized guns for the conversion kits and ammo.
If you've got an AR-15, consider the CMMG kit as a way to reduce training costs.