I have successfully installed several JM Pro Mac Kits in the FWB124 rifles, mostly because piston seal has disintegrated and was pounded into the end of compression tube, the old "gun would cock and shoot but no pellet would exit barrel issue". I recently acquired a standard model 124 not the deluxe model like my other one. The other 124's that I rebuilt I ended up installing a full power Pro Mac Kit with great success. My 124D has over 2000 rounds through it and is smooth as glass and shoots JSB 8.4's at 840 fps and the lighter 7.3's at 900 fps accurately. Well I ordered another Pro Mac Kit for the standard 124 and it seemed to overpower the gun, was shooting harshly and very jumpy unlike the other 124D. When I shot across chronograph the velocity was hotter than I would have liked. The 8.4 JSB's where 870 fps and the 7.9 JSB's where 900 fps. I tried shooting several hundred rounds through in hopes gun would settle down but it didn't. I ended up taking gun apart and putting factory spring back in and velocity dropped back down to 740 fps with JSB 7.9 and gun was not nearly as jumpy but the spring twang returned. I let gun like this for a while with the factory spring but eventually ordered the JM Pro Mac Slightly Softer Kit. After installing the slightly softer kit and shooting I realized this was the way to go for this particular 124. Spring twang vanished, cocking was smooth and easy and to my surprise velocity with a 7.9 gr JSB Exact was a consistent 760 fps. I'm sure after kit breaks in velocity will be even better and things will smooth out even more.
FWB124-Testing Different JM Pro Mac Kits.
- Thread starter bzizzi373
- Start date
Good to hear. I’ve tried all sorts of spring/seal combinations in my springers. The sweet spot always seems to be somewhere between 11 and 12fpe. I’m also partial to the JM springs. They deliver a more mellow shot cycle than the Vortek springs.
R
R
Upvote 0
More than a few folks have had the same experience and have reported great results by using the higher powered spring and leaving the gun cocked until the spring takes a set at the velocity they are aiming for. This could be especially helpful if you are looking to achieve a specific goal such as coming in right below 12 FPE for field target etc. I have not tried this myself yet but I can say that I have shot several guns that were "Tuned" this way and the results were excellent. Be aware this could take a few days or a few months to end up where you want to be and if you don't like the results you will be looking for another spring. I am considering this on a gun that shoots a little hot now and I would be buying a new kit anyway. Costs nothing to try.
Upvote 0
Thanks guys
I like reading about the FWB 124, I have a S model I bought when they 1st came out, I always thought nothing could out shoot the FWB. Mine still has the Blue Ribbon 6x32 model scope , One of the best at the time, The PCPs opened my eyes and proved me wrong big time, All my springers are pretty well gun safe queens now ,
ten years have gone by quick since I jump on the PCP band wagon.
Mike
I like reading about the FWB 124, I have a S model I bought when they 1st came out, I always thought nothing could out shoot the FWB. Mine still has the Blue Ribbon 6x32 model scope , One of the best at the time, The PCPs opened my eyes and proved me wrong big time, All my springers are pretty well gun safe queens now ,
ten years have gone by quick since I jump on the PCP band wagon.
Mike
Upvote 0