On the 8th Round Fired (7+1) on a brand new Ruger 7 Round Extended Mag it took the final casing and loaded it back into the magazine resulting in a locked back slide and a jammed magazine. Took considerable force to remove magazine at which time the case was still in the magazine. Didn't think to take photos. 1. Ammo - Aguila 95 Grain FMJ. 2. New Ruger Extended Magazine 3. Stoppage was the last round fired out of the first time this magazine was loaded. 4. 100 more rounds fired through magazine without repeat. 5. 508 rounds through the gun at time of stoppage. Anyone seen this stoppage before? Cause?