A pistolgrip fore-arm, used improperly, will torque the forearm and screw up the weapon.
One reason you rarely see them in use by anyone who knows what's up.
If it's not locking up without a lot of force forward, something internally is not right, and you should have a good shotgun-wise gunsmith check it out.
"And Shepherds we shall be. For thee, my Lord for thee. Power hath descended forth from thy hand, that our feet may swiftly carry out thy command. So we shall flow a river forth to thee and teeming with souls shall it ever be. In nomine Patris, et fili, et Spiritus Sancti. Amen."