can you be more specific on the what is happening when it jambs or short cycles. The cycles of fire are: feeding, chambering, locking, firing, unlocking, extracting, ejecting, recocking, and then the process starts all over. If you can be specific on what is exactly occuring then maybe I can diagnose the problem. Have you tired different magazines? Have you cleaned and well lubed the weapon system also? The ammo from Blackhills is usually good stuff, but have you tried others like Federal?
Also are you in the metro twin cities area? If so maybe we can go to the range and I can see what is occuring.