I have this exact problem with my S-12. My problem was I wanted to shoot 7/8 oz slugs at ll00 fps, the 1 oz slugs at 1200 fps would do what your gun is doing. Anything at 1 1/8 oz would run fine except Winchester. I won't buy Winchester any more, it just does not like my gun.
After tallking to Pauly we think that when the mag still has ammo in it, the round still in the mag is pushing the spent rounds out. But when the mag is empty there is not that round helping the fired round to eject. The bolt is short stroking and it needs some work. Send it to Pauly and have it given the Glass Bolt tr
