Sam I have had a JM kit in my old model 34 from 5 years ago. Well, it was bought new then and I soon installed a JM kit and unsure of the exact kit it was. What is did was smooth the shot cycle and really level that gun out to be a very great shooter. It even took away most twang from that spring. It was a .177 caliber.Now in my Weihrauch HW97K I have now I installed a Vortek PG2 kit and it made that gun unbelievable to say the least. Smooth as gooey butter! The fps increased about 10 fps and the twang definitely all gone in that gun. Made a already excellent gun into a true competition gun if I competed.Hope this helps.......