As you guys remember, I picked up a late '80's mil-spec last week. It's worn, but does not appear abused or neglected. Here's the deal. When trigger is pulled, it will occasionally, drop the hammer to the "half cocked" position. It may do it after three rounds, then may skip ten then may skip five. I will be doing a bit of work to this Springer, plan to replace nearly everything but frame, slide, barrel & bushing. Any clue what the deal may be?