The lineage was OMC - Ordnance Manufacturing Corp.
3-5 different versions/locations of AMT - Arcadia Machine & Tool.
and finally IAI , Irwindale Arms Inc.

Their guns were of very good design. The problem with later AMT or IAI guns is that they sandblasted every square millimeter so coarsely , the moving parts felt like dragging a brick thru wet concrete. A bit of stoning and polishing really slickened these guns up. I recall the .22 mag would run only with either Win or Fed ammo. Can't recall which one. Yeah , they had a good bark and muzzle flash too.

I slickened up mine and several others .380 Back-Ups and they've proved very reliable.