FWB 124 Sporter air rifle

by Paul , Tuesday, July 25, 2023, 15:53 (422 days ago)

One of the local gun club members brought me his old FWB air rifle to see about doing a complete maintenance job on it. It was completely original, purchased back in the 20th Century. A bit of toilet paper over the breech/transfer port junction was blown clear on firing - bad breech seal. So while up north this year I took delivery of a kit from Air Rifle Headquarters' Jim Maccari. He's been the "go to" guy on top end spring rifles for some time now. Finally got a chance to play with it a bit over the past several days. Replaced the breech seal and solved the leak there. Ran a short string and got an average of 760 fps with 8.44 gr pellets. Got it apart and found that the piston seal was already separating, held in place by about 30% or so of the circumference. Installed the new seal, polished the spring ends, dabbed some moly grease here and there, installed the "top hat" and spring and piston and such and did a string over the chronograph. Things had improved a bit, but Maccari included a "power washer" to up the preload a bit. So I put it in and got some gains. We ended up with an average of 785 fps over 20 shots and an SD of just under 5. Not too shabby!

In case you're wondering - yes, malformed skirts on pellets affect velocity. I was dipping straight from the tin and saw that one of the pellets I'd just stuck in the chamber had a dented skirt. Well, I've read that those skirts will "blow out smooth" with no loss of accuracy or power. That ain't necessarily true. Ended up with only 744 fps so that shot got tossed out of the reckoning.

The original spring was 41 coils or so, this one is 28. I"ve misplaced my calipers so don't know the difference in diameter, but the new spring is much heavier wire. I wanted to put a soft spring in, but the owner wants "all I can get out of it" so we went with the stiffer, more powerful spring. I suspect it will pick up power over the next few hundred shots as it all beds in. Here's the final string I shot with it.

Feinwerkbau 124 Sporter JSB Exact 5mm power washer Altitude
ARH Jim Maccari kit 8.44 gr 4135.0

Shot # FPS FT-LBS PF


1 775 11.26 6.54
2 777 11.32 6.56
3 781 11.43 6.59
4 784 11.52 6.62
5 791 11.73 6.68
6 785 11.55 6.63
7 795 11.85 6.71
8 788 11.64 6.65
9 784 11.52 6.62
10 787 11.61 6.64
11 790 11.70 6.67
12 786 11.58 6.63
13 788 11.64 6.65
14 786 11.58 6.63
15 788 11.64 6.65
16 783 11.49 6.61
17 787 11.61 6.64
18 781 11.43 6.59
19 777 11.32 6.56
20 785 11.55 6.63

Min Max AVG TrueMV
775 795 784.90 784.94


Spread StdDev
20 4.94