Last fall I replaced the spring and seals in my .177 cal.48 with a kit from JM (GTR kit)with a loss in fps.of over 100 fps. (before ave.860,after 735)this is with Beeman Ram Jet 9.8gr.pellets.I asked for and recived much good advice for everyone,from to much tar on spring,bad piston seal,bad breech seal,etc.I decided to shoot as is for a while to see if there was any improvement.after about 500 rounds I checked again,no improvement so I replaced the spring kit with an RWS spring only,velocity jumped up to 880fps.
I have used JM springs and seals in three mod.34's with only a slight loss of speed (20 or 30fps.)What have I missed or done wrong? JM makes the best aftermarket springs and seals out there IMO so it has to be me.Help. Thanks guys,Gary
all his GRT kit's come with the spring pre-set, meaning the coils are already compressed
buy the spring alone and it does not come pre-set unless you ask for this service and he will charge you $1.00
after 1,500 to 2,000 pellets all springs will set, a spring not set is 11" long a pre-set is 10". the set is 1" shorter
the solution for the GRT kit is to add steel "washers" to the rear guide until you get close to the original FPS of the OEM spring
if you buy the unset spring after a while you will have to add washers too, so why not do it at the beggining with a set spring. that way you do it all once and not have to open the air gun to do it later
the JM spring will last longer than the OEM spring IN ALL CASES, why? because of the .128 dian.hardened wire he uses and other things he does to his springs. there is no mysteries in his springs if you know the mechanics of "COILING" a wire. turns, open end, compression load, etc.
warren
and remember "it's 30% the gun and 70% the shooter"
don't listen to Tim on this one, he will get Mickey Mouse and Minnie banned from the Magic Kindom in Orlando and California if they listened to him LOL
do your basic pre load on the spring and figure out how many washers, test first with the OEM spring for fps and then change spring to the JM
cumbersome?? YES tedious, absolutely but you have to get the right mix to get the right FPS
to many (washers) and you will pre load the spring to MUCH and it will be a bear of a shooting cycle, not enough and you have not achieved the 100% efficiency of the spring
first one washer and chorny then another and such until you get the right arrangements, should be around 11" total lenght with rear guide, washers, top hat and spring
if only using the spring without top hat, etc it is still about 11" TOTAL lenght
warren
PS: problems understanding, then e-mail me DO NOT call 911 LOL
and remember "it's 30% the gun and 70% the shooter"
Well Warren and all the rest,I installed a .120 thou. thick washer and got to try the rifle today.Velocity went from 730 fps to 790 fps. I am going to take it down and add some more.I would like to get it shooting in the 860 to 880 fps range.Thanks again Warren for the tip.
Gary
Warren's new nickname is "Spring Man"! I 'm not joking. Tim knows It's a well deserved, honorary title for a really nice person that is always helping and looking out for people.
Actually the washer-for-power spacing has been discussed here several times, especially with JM springs, but the credit goes to Warren for fixing Gary's gun. Nice going Warren!
You are right Harry,"Spring Man" Warren has a heart the size of Texas! He knows more than just springs, A powerplant Guru for shure. He shares his knowledge freely,& always is there when I have a question, with solid advice. Congrats. on your sucsess Gary! Like Warren says, a little at a time! LOL! Tim.
First, it doesn't take 1500 shots to set a spring, just one cocking cycle will do it. 1500-2000 shots later, the spring (factory springs especially) may be starting to fatigue and lose a bit of power, showing the beginnings of spring cant, etc. A bit of spacing may bring power back for a short time, but its a temporary fix at best. Since the spring is already starting to fatigue, while the gun is apart just replace the spring instead of putting in washers.
Many of JMs springs need spacing to work correctly. He does not make a separate spring for every make and model, rather he makes a couple dozen sizes that are sold individually or installed in kits for specific model ranges or chamber sizes. Some of his kits do come with spacers, but some don't. The majority are not drop-in factory replacements, and he does specifically say so. Jim does not supply installation directions with his kits as he feels that if you don't have the wherewithall to do it right you shouldn't be doing it. He is kind of funny like that. Anyay, adding spacers is the key to JMs kits, but not necessarily at the rear guide. Many times adding the spacing to the front of the spring inside the piston will get better results, since you are not only adding preload to the spring but also adding mass to the piston. This needs to be carefully regulated though, as too much weight in the front can result in a harsh firing cycle.
You don't really want to be taking the gun apart a dozen times to add spacing a tiny bit at a time either, as every time you take it apart you risk doing damage to screws, threads, triggers and most every other part. What you want to do is compress the old spring to its stacked height, measure it, then do the same to the new spring, and make a spacer to take up the difference accordingly from a single piece of delrin, nylon or whatever have you. Do it once and do it right.
Here is an example of spacing a spring- a JM FWB124 short-spring kit with correct spacing. The spring is a couple inches shorter than a factory spring, but with this set-up the gun now shoots at 900+ fps. (Remember what I said before- spring length is irrelevant)
Well guys I replaced the .120 thick shim with a .160 thous.shim and the vel.dropped down to 785 fps.so it is back to the drawing board.I refuse to be whipped by this.Gary
Its possible that although the seal is appears intact, it may be a bit tight in the cylinder. This may account for the velocity loss. Its also possible that the spring wasn't meant to deliver 850 fps in this gun. JMs kits are designed more for smoothness than power, and what you have may be all the spring can handle. His description says "moderate high power", not "full power". Best bet is use the factory spring if you really want power over all else.
Dave (Arathol) thanks for clearing the spring set up. Iam new to tuning and really became confused at the other post. I have been watching MZ tune a few guns and learning all the time, but thought maybe I wasn't paying attention and was just about to give him a call. I will take both post with me next week when he tunes my R7, and use as a reference to ask questions. By the way, weren't you the one interested in the chrony results of my detuned 34? I received a call from him yesterday and he had just completed the detuning of my 460, and HE was excited as a kid under the Christmas tree.(obviously the suspense is killing me) Unfortunately I had to work yesterday and can't pickup the gun until next week as he is going out of town. If you are interested in those results e-mail me, as I doubt that I will post them or the 460's on this site as most guys here seem to be more of the power bunch and not much interested lower velocities. I do remember one thing that stuck in my mind that I had heard before that was your comment "DO IT RIGHT THE FIRST TIME"! and you will have a gun that last for years. Please keep posting, we don't hear enough of you!
Dave (Arathol) Sorry, for the mistake. I inadvertently thought you were the guy that wanted the chrony results. I received 4 emails today and realized it was other folks that wanted the results. Sorry for the confusion.
Keep up the good work!
It's a well deserved, honorary title for a really nice person that is always helping and looking out for people.
