Anything within .001 of the bore sizes they provide
Ultra accurate, low cost, fits milsim hand guards
Not ceramic (self cleaning)
As part of a recent string of upgrades, a new barrel was deffinately a part of the list. I picked this kit up for 30 bux (at manufacterors cost) and same day played five or six games with it.
This barrel absolutely destroyed my stock barrel. I was shooting nelson special forces paint, which was .690, and i used the .691 bore. With the front, the barrel's 16" in all.
It was more accurate than even my J&J, but i was sort of expecting that.
The difference became clear the very first game i used it. In one such shot, maybe 100 feet across the field, my target was right out in the open, i had him. Normally with my stock barrel, it may have taken 30+ balls to just hit him once. I quickly sweet spotted my hella fast RT and put about 10 balls his way in about a half-second, and 4 of them hit. Not bad considering i had basicaly no time to aim.
Later on i did some strait up accuracy tests. This barrel when sized apporpriately to the ball will land them ball on ball. The accuracy is astounding for such a low cost.