Yak-9U has 1x 20mm with 120 rounds, and 2x 12.7mm with 170 rounds or so each. Still, I took out a spitfire and 3 B24s in a single sortie once. I had to set the last bomber on fire with just the 12.7mms, and it took 3 passes after I ran out of cannon, but I did it!
So, basically, my point just now is ... well, probably obvious, but aside from that, my point is, there are some plane much better suited to it, but ANY plane can kill bombers, regardless of the lack of weaponry onboard, as long as it can CATCH said bombers. Don't shy away from early 109s or yaks etc. I wouldn't choose 'em as my first pick, but once you get more used to it, have some fun.