I recently purchased a new S&W performance center 44 magnum and got a chance to shoot it yesterday. It is deadly accurate, however, I have a problem. After the first 6 or 7 shots I had trouble cocking it. I thought maybe the lock was activated but no. I got it to cock and it fired ok for 3 or four shots and then it was difficult to cock. It seemed to be completely random. Without ammo it cycles perfectly. Nothing was under the extractor, it was factory speer 240 grain ammo. No drag marks on the front of the cylinder and no drag marks from the spent primers. Ideas?