Maccari sold these springs for the FWB 124 separately a couple years ago. It is a shorter spring with one end wound so as to fit the spring guide on the trigger very tight. You have to for lack of better term screw it on, thus the term twister. It is a full power spring giving velocity's around 830 with 7.9gr pellets. The goal is full power with less vibrations. I replaced the bad seal, installed the twister spring and lubed the spring with Moly, the piston seal with Krytox 205. Now that I understand lubes a bit, moly and krytox should not be in the same area's so that needs rectified on this tear down. I'm thinking after this last round of suggestions I may look at Macarri's soft kit.
Installed Macarri's Soft kit for the FWB 124. Macarri advertises 5 per cent less velocity over his full power kit. Kit came with a spring with top hat installed. Spring was a few inches shorter than the spring I had in it. Spring fit the trigger spring guide loose but too tight for a guide. maybe some shrink tubing would have worked but I wanted to try it without. Since I had just installed the seal I reused it. Velocities with the twister spring averaged 797fps over 10 shots. Extreme spread was 11 ft/s and SD was 4 ft/s. Rifle had about a thousand rounds on this kit. The Macarri soft kit was installed and I shot it 25 times then shot 20 rounds over the crony. Average was 761 fps, extreme spread was 34 ft/s and SD was 9 ft/s. Shot cycle is smooth with some forward jump not much. All shots were with 7.9 Crossman's. Strange the efficiency went down with the advent of the new kit even though same seal and piston was used. Here is a photo of the new spring with top hat compared to the twister. Spring wire on the twister measures .130 and Soft kit wire diameter is 125.