A shrine built for a Feinwerkbau 124 – Part 6
by B.B. Pelletier
Tuning by Earl “Mac” McDonald
The saga of tuning the FWB 124 continues. While he was here, Mac replaced the Mongoose tune in my 124 with a fresh Maccari Old School kit, which consists of a Blizzard piston seal, a short mainspring and a spacer that slides inside the piston ahead of the mainspring. This he cheerfully did.
You may recall that my 124 was giving an average of 800 f.p.s. with the Mongoose kit. I felt that was too slow and wanted just a little more — perhaps 840 with Crosman Premier lites. The words on Maccari’s website seemed to indicate that the Old School tune was the ultimate way to go, so I ordered one.
The kit arrived, and I was going to install it when the hospital adventure began. So, when Mac arrived, he had the time and I asked him to do it for me. He certainly knows how.
He had to use my mainspring compressor to get the rifle apart but was able to put it together with the Old School kit without using the compressor. No Black Tar dampening compound was used with this tune because the Old School kit is supposed to fit so well it doesn’t need it. Mac put some moly grease on the outside of the mainspring and buttoned up the rifle.
In the hospital, I waited with great anticipation for the results, which came the next day. According to Mac, the new tune averaged around 740 f.p.s. with Premier lites. Seven forty! I was devastated! Well, maybe Mac was reading the chronograph wrong. I vowed when I got home that I would check it.
I asked Mac to remove the hump on the piston seal, thinking it might be the cause of the lower compression. He used a Dremel tool rasp to cut the crown smooth, as I requested, but no change in velocity. So much for my theory of the wasted compression space caused by the high crown.
I shot Premier lites and got the following velocities:
The shots were accompanied by a burning oil smell, so the powerplant may be over-lubricated at some point. I will disassemble it to determine what to do next. On some guns, I might suspect the compression chamber.
I’ve examined the 124’s compression chamber and know that it is in good condition, but allow me to show you one that is not. Remember the Slavia 622 rifles I tested for you a while back? If not, read this.
What to do?
My next step will be a teardown to check what’s going on inside this gun. I may be able to refresh the tune and get it up to snuff from there. If not, I may install another type of piston seal left over from 124 testing years ago. The journey continues….