Rebuild my 48, questions!

[hzyl0402]

Hey guys,

Thanks again. And last night, I tested my gun, and I found out it's loader than before tuning. is it because I reduced the amount of heavy tar on the spring?

Liang

[Mark 611]

muzzle loud?

[s10gto]

If muzzle loud very possible. By reducing the tar the FPS will go up.

[Jaymo]

If you can ever afford a JM tune kit for your 48, it's a good one. I put one in my B30 a couple years ago. It went from a rough, gritty shooter to a smooth shooter with just a JM tune kit, JM seals, and the proper honing/polishing.
I've been using dry moly spray on the front/rear of the piston.

[s10gto]

Got a JM VRT tune kit in my 52. Very smooth and puts out 18 FPE.

[hzyl0402]

The spring and seal in my 48 are all from JM, and it's the new ZRT kit. As you can see from the picture, I have barrel shroud. Before tuning it's as load as my Daisy 953, which is a single pump target rifle, shoots around 400fps with JSB 8.4g. But now, it's much loader. I think the barrel shroud will cover most of the air blast, maybe the extra noise is from the piston hits end of the compression chamber?

Liang

[s10gto]

What weight pellets are you using? My 52 has the VRT kit and in .177 with 10.3 grain shoots high 800's for 17.5 to 18 FPE. The ZRT kit is a higher power kit. With a pellet too light it will be loud. Can sound like a rimfire .22LR. The piston can also hit if the pellet is too light. 

[hzyl0402]

What weight pellets are you using? My 52 has the VRT kit and in .177 with 10.3 grain shoots high 800's for 17.5 to 18 FPE. The ZRT kit is a higher power kit. With a pellet too light it will be loud. Can sound like a rimfire .22LR. The piston can also hit if the pellet is too light. 

I only use JSB heavy 10.2g. Of course it's quieter than the factory version, but it's loader than before tuning.

Liang

[s10gto]

That should be just fine for pellets. With the ZRT kit it is probably close to 19 FPE and is normal. 

[hzyl0402]

By listen very carefully, I can tell the firing sound combines a solid hit sound, a sharp hit sound "ding" like 2 metals hit each other and last a low and solid "bu" from muzzle. Obviously the sharp hit sound "ding" the extra one and makes my gun loader. Is it because of the new seal I dropped in this time? Maybe it need more rounds to break in? Any one get any idea about that? Any previous experience on new seal?

Liang

[s10gto]

Does sound a little strange. As far as JM's seals I have never had a single problem with them. I have had many. Only thing I can think of is check the Allen screw in the end of the compression tube that holds the cocking rod lug. I have had that loosen up. Maybe you are hearing it move upon firing. It would also not hold the breech seal tight to the barrel. After it is tight your cocking lever should be 2 1/4 inches from the receiver before it locks shut.

 

[s10gto]

This may help too. 

http://www.google.com/url?sa=t&rct=j&q=rws%2048%20tunning&source=web&cd=1&ved=0CCEQFjAA&url=http%3A%2F%2Fhome.comcast.net%2F~scot_for_sale%2Fguns%2FRWS48_tune%2Findex.html&ei=ecezTo6mOcOq0AGjspCdBA&usg=AFQjCNHEqrgqLj_uOU6tUIE53bXmwlVQIQ

[Mark 611]

Did the seal fit kinda snuggly in the compression tube when you put it in? If not your probably getting some piston slam also how'd the spring fit on the guide was it tight?

[Bullit]

That's also what I'm thinking by your description of the sound... Piston Slam.
Liang, you also have posted that you had damaged a Leapers UTG scope with this air rifle.  Piston Slam will kill any scope.

[hzyl0402]

That's also what I'm thinking by your description of the sound... Piston Slam.
Liang, you also have posted that you had damaged a Leapers UTG scope with this air rifle.  Piston Slam will kill any scope.

That sound just come out from Wednesday after tuning, during the tuning the only part I changed was JM's seal. When I install the piston, I feel nice and tight. And the viberation don't have any change. Maybe it's not the problem you guys worry about. But I am not sure.
Actually I am just back from range, I am happy with today's shooting. After the whole tuning kit break it, it may become more smooth.

Here is the groups at 25m.

[Bullit]

Well Helles Bells Liang!  There's not a thing wrong with those groups at 25.  You made us worry too much!  Keep practicing!