Hi all I have recently purchased a VFC M4 e series which is absolutely blinding, however the only disappointing thing is that it didn't come with a tight bore barrel so I'm going to stick one in. I was also looking at a new hop unit, at the moment I'm looking at the madbull ultimate hop unit but have heard metal units can cause the bbs to scratch and lose accuracy so was just wondering if anyone could recommend another unit or any other suggestions. Cheers