I have a TX200SR in immaculate condition. It has a small problem with consistency.. It shoots AA 8.4gr at 770-775 fps and every 4-8 shots one or 2 shots are slow [in the 740 to 730fps region] The recoil also feels different for the slow shots.. I have changed the main spring and guide to a custom Maccari kit, piston seal and breech seals. I have relubed everything correctly but it still does the same. I have tried JSB Express pellets and the same thing happens...a slow shot every now and then.. Accuracy is very good but the consistency worries me...any ideas?