I have a Spikes Tactical 22lr upper, I've put at least 3,000 rounds through it so far. BlackDog magazines and WallyWorld bulk pack Federal ammo. Mine doesn't like anything else. It's filthy right now, but I could take it out and run another 500 rounds through it and not worry a bit. The thing is like the Eveready Energizer Bunny on that ammo. Fairly accurate, about 1 1/2 inches at 50 yards. Super fun to shoot and you get a lot more trigger time at a fraction of the cost. Helps you become a better shooter.
I don't think Spikes makes dedicated 22's anymore, but Tactical Solutions here in Boise makes a killer upper, a little spendy, but from what I've seen, well worth it.