I built an Imp for a friend and we used it yesterday for the first time.  He was frequently getting a bolt/hammer forward condition and blowing air.  Shot shot shot fizzzzz; pull it back and repeat.  Even with a full HP tank.  All lubed and clean.  This is the only one of my 5 imps that does not have a tapeworm.  All standard internals on a serial # 26785.  No LPR.  Pressure is @170-180 firing at 280 fps with a Dye Boomstick.  Decent ball seal, but not as good as a freak.  I have gotten this on occasion with other imps, but this one is a lot more frequent.  Thoughts?