pretty much any kind just match the paint with the bore
I honestly havent found any
I was a bit skeptical about getting this barrel system because they were so rare and there were so little reviews, but Im glad i got it. I got mine brand new off of ebay for $51 and I think it might be the best barrel system ever made. I can hit almost anything with this barrel it has just been wonderful. I mean i have even shot ppl that from about 50 yards (no it doesn't add range) but the ball will stay straight no matter what the distance.
It is dead on so if you get a good deal on this like i got make sure you buy it because i honestly dont think you will find a better barrel. I would give it a 9.5 because nothing is perfect but im gonna bump it up to a ten cuz it is so great.