Having had both HW99,s to fit V Mach kits,the .177 not as pleased with the outcome as with the .22 which was a nice and well behaved,I always polished the piston and also any washers to remove even the smaller bur the lightest amount of grease.Have seen 99,s and other weihrauchs fitted with so call tuning kits and thought them only slightly better than the factory so just a polish and a tidy up of the spring ends can give just as good results