A little while back I posted that my .177 48 crono'd CP lites at an average of 905fps. many said that it was on the low side for the gun. It shoots accurately and smoothly so I have been content to just go with it. Curiousity got the best of me and I decided this evening to take a look inside the gun.
I'm mechanically inclined and taking the gun apart was pretty easy and I found the inards to be completely dry of any lube at all. The mainspring is bent into a slight "S" shape when out of the gun also. The forward end of the spring guide is a bit chewed up also. The seals looked fine and there were no visible blemishes on either. The piston seal seemed to fit looser in the compression chamber than I expected but I dont know how it should feel. I dont have a spare spring or guide so I just used some moly and lubed it up sparingly and put a very light coat of grease on the spring and put everything back together. I didnt get a chance to crono it but shooting it inside, it seemed to feel the same. I put about 30 shots thru it and it seems okay but I am thinking I am better off with a good spring and new seals..
It seems that I can do any tuning myself. I have all the means to polish and debur anything and this place seems to have every diagram, instruction and how-to's explained in great detail. Im deploying in the AM to Japan for a couple months so I figure I can order the parts and when I get home they will be here and ready to be put together.
My question is what to order? I want to keep the power up as I like to shoot pests, etc and recoil doesnt bother me.
maybe a new stock mainspring with a maccari large apex seal properly sized is the best solution since you want to maintain power. if you don't want to order
the tar from him (best lube for the spring) i can send you one of my extra ones that he sends with springs. no charge. least i can do. i also have a little used stock spring you can have. send me your address stateside.
Well, I'm gonna try out the stuff from Larry but I definitley have a seal issue. This afternoon I crono'd the gun using the same CPL's and my average FPS is now 967fps,up from 905fps before I tore the gun down and lubed it up.. However, I can shoot 10-15 shots with maybe 1-2fps variance and then get a shot that is pushing 1000fps or one that drops to 850ish. These are flukes that are only occuring once every 10-15 shots. So I'm gonna order a new set of seals and see how it goes.. In the interim I will polish things up and smooth her out inside as best I can and when I get homw see how it works out.
is pushing the accuracy envelope. when you are gettng a thousand you may be eating a little lube and getting some dieseling. ideally i think you would want to be around 950 tops. when you use the tar use it very sparingly or it will slow the gun down.
I was thinking the same thing as the pellets are probably transonic at that point. A little update though. I took the gun apart again to try and see if I could find any damage to the seal and explain my occasional velocity spike or dip. I found that the spring guide was binding on the rear extension of the pistion. The forward end of the OD of the spring guide was rough as I noted before but when I looked closer I found that it had a section dented inward and it was binding the piston extention when it seated inside it. So I gently cut away the material on the ID restoring the guide to it's original ID, polished up the rear of the piston at the flare, went over the gun with a fine toothed comb, lubed it up and Im off right now to see if that was the cause of my quandry.
break those sharp edges on the front face of that mushroom shaped tip on the
piston stem. i am talking about that flat face that leads into the guide when cocked. i polished mine on a polishing wheel as well. that can hang up and also chew up the inside of the guide. i will include a guide in the package. all you need is the right size rear washer for the 48 action tube, which you have. i have metal guides in my 52 now. you could probably have rich in mich make some for you but you would have to send the spring to him.
That did the trick.. I crono'd 40 rounds and it averages 985fps with very little deviation. I guess the erratic spikes and drops were from the guide binding the piston extention. I appreciate all the help and I will stone the parts you pointed out when I get the stuff. Now I wonder where my accuracy will be as i wasnt really testing for that but Im assuming that since the rounds are definitly in the transonic velocity that it probably dropped off some?
What really surprised me was the gun was literally dry inside from the factory, no lube anywhere. I lubed the seal OD(none on the face) with moly grease as well as a light application on the piston extention and the OD of the guide. I used plastilube grease on the spring itself, a light coat. I will put the tar in when I get it though. Didnt think this gun could be so finicky.