shoot through hop up?
 

is that any knid of hop up unit that has no chamber, just a hop op and barrel that the bb enters when fired?

im working on a shell ejector project and i want a barrel assembly the uses the shell as the chamber, and most i can find have the chamber integral to the hop up unit

thanks

Most pistols and sniper rifles are that way... Look for a VSR-10 barrel and hop-up system, or APS-2

GBBR Barrel will also work if what your trying to do is what I think your trying to do.