Sure, it would be fine in a PT-20.

Looking ahead, since you mentioned combat, the Mag .25 is ok in combat, but nothing really exciting. I have a couple of Mag .25's and Mag .28's. The .28's are slightly lighter and produce noticeably more power. (It's exactly the same engine, just a different piston and liner). The OS .25FX is about on par with the Mag .28, maybe a little more powerful. The Irvine .25 is competitive, and the right now, the Webra .25 is really knocking the socks off of everyone, that thing is a screamer for the same price as the OS. But the Mag .25 isn't a bad engine to get started in combat with if you can't afford the OS or Webra.