I purchased a used RFB carbine about 2 months ago and after a few times shooting it, I've realized not only is it missing the birdcage, but the barrel end isn't threaded. Anyone know what gives?

Hey everyone, this is my first post and I was just wondering what the best compensator to put on the rfb would be? I'm looking for something that would reduce muzzle climb but wont blow any gas or anything back in my face. Thanks for reading!