[Styrak]

How are you chambering the first BB?

If the hopup isn't on far enough the 150% recoil spring might be forcing the BB past the hopup, hence the rolling out of the barrel.

I have a Guarder metal slide and a 150% recoil spring (really snappy) and I have to keep the hopup at >50% to keep BB's from rolling out the end of the barrel when they chamber.

Maybe that's the problem? Although you said you tried all settings....hmm.