A5s, are recoil operated, so they are finicky as to the type of ammo they shoot. There is a buffer that creates friction on the recoil spring. If you have a magnum buffer setup and fire standard loads the gun wont cycle right, if you have a standard buffer set up and fire magnum loads the gun will tear itself appart.
A5s, are heardy as hell, but the desighn does neeed to be opperated right, so you dont destroy it. If i were you i would do one or both of these things,
Call AGI and get thier A5 armorer video
Call Browning and get a owners manual for your model gun.
Chnaces are you DO not have the magnum buffer set up on that shotgun, so dont shoot magnum loads through it, untill you are sure.
Have fun, its a real nice piece!