I'm getting ready to do some real tuning on these rifles of mine and have noticed over the time I've been shooting them the factory spring's are inconstant, example One rifle may shoot 1034fps another may shoot 980fps same caliber! so I know thier are alot of inconsatancies from gun to gun an part to part remember these are Chinese gun's and thier QC is not perfect from run to run on anything especialy airgun's, and we all know these gun's need work on them. I've already done alot of work on the ones I have and now I'm gonna take them a step further in the tuning process and I'm looking at part's from JM and Vortek and other's to see what I can come up with to improve what I have in my TF89 or AR1000 type rifles, none of them have factory barrel's on them all are Lothar Walther barrel's and yes I know these gun's to some are not worth putting this kinda time or money into as I'm doing but they do make exelent field gun's powerfull and very accurate with these barrel's on them, and this keep's my HW's an Beeman's from the I'll's of my outdoor adventure's, I'm open to any suggestion's from anyone on piston seal's [etc] to make these gun's the best they can be for some long term use between tune's! I like these gun's yes thier crude but can be turned into nice field gun's for not a whole lot of money, ya gotta keep'em tuned so why not put the best sfuff in there as possible and do what ya can to make it the best it can be!