The Aquila Colibri's can be incredibly dangerous to use in semiautomatic rifles.

These are a 22 long rifle loaded with only a 20grn bullet and propelled only by the primer.

When used in locked breech weapons like a single shot or bolt action, function is typical of any other load, even though they're incredibly low velocity - seems like I recall reading 300-400fps, even with the piddly 20grn pill. In sealed breech/locked bolt weapons, the primer has more than enough power to push the bullet out of the tube.

BUT...

In a blowback semiautomatic action, your bolt may open however slightly and the case may not obturate properly to seal the gases into the bore, so the breech blast vents too much power out the side. The bullet stops in the bore. Then the NEXT shot will sound a lot louder, and will often fully cycle as it slams the second bullet into a plugged bore.

Too late, damage is done.

I've seen this happen twice in my life - once in a Marlin 60, once in a Ruger Standard pistol (Mark I, before the Mark II or Mark III). Bulged the barrel in the Ruger.

So sure, in a single shot or bolt action, I don't mind playing with these, especially in a situation where I'm able to verify the bullet left the bore for every shot. But I'd never use one again in a semiauto.