exerlent design but poor mesurments render it unuseable without modifications, firstly the concave nub that is biult into the hop arm is to big and slightly off center and the angled cut in the arm that is to moove the arm up and down is off and has a bit of play in it rendering it unusable cos it basically goes from hop fully on to hop even further on to rip ur bucking and as its fully on all the time it wont allow a bb to even pass throuh so youd need to find an aftermarket arm like the pantera or similar, then there is the bb catch... if the unit is tightened to a normal level then it slightly pinches the ally bb catcher putting more resistance on it meaning either feeding issues or if the shell is to tight like i found out the hard way then the cylinder knozzle hits it hard when racking the bolt then damages the ramp on the bb catch making it worse so again ull want to use ur standard one, but, if like me you can no longer be bothered to tech the heack out of it then just go for the action army hop unit instead, its a shame this one, bit of a missed opertunity as it could have been epic... whish i could say i had a bad one but iv been giver 6 to look at so far an they all have the same problems