A shrine built for a Feinwerkbau 124 – Part 4
by B.B. Pelletier
My enshrined 124.
Today, I’ll complete the tune on the FWB 124. A couple people have asked about this gun. What makes it so special? Well, it’s lightweight, accurate, easy to cock and shoots like a dream. It’s the very rifle AlanL has been searching for but doesn’t realize it.
Back in the 1970s, when the FWB first came to the attention of airunners, it was considered one of the most powerful springers available. Together with the BSF S55/60/70 and the Diana 45, it was one of those rare air rifles that would sometimes shoot faster than 800 f.p.s. Today, we wouldn’t give it a second look with numbers like that and here is what we would miss. We would miss owning a Mercedes SSK convertible, just because it doesn’t go as fast as a Mustang SVO. Nobody would give any thought to the fine coachwork, the burled wood dash or the exotic leather seats. No, they would all be focused on the speedometer and miss one of the finest examples of its kind ever to have been built.
What to expect
With a modern tuneup, like the one I’ve done here, the 124 should top 840 f.p.s. with Crosman 7.9-grain Premiers. I showed you the tuneup kit yesterday. Today I’ll install it along with some lubrication that I always do on a 124. Of course, this is one more reason for owning a chronograph.
Cutting up the old seal
Before I begin, I had some comments that I will now address. First, someone asked me how I cut the thick piston seal to remove it. I mentioned a special knife that I’d like to show you. This tanto-shaped blade comes on a Gerber Crucial multitool that Edith gave me for Christmas. I keep it in my desk drawer and it is one of the handiest multitools I’ve ever seen. The knife blade is very stout, so it handled this job like a breeze and a few passes over the Warthog got the blade sharp in moments.
A Gerber Crucial multitool has a tanto-shaped blade that was ideal for cutting the old seal into pieces, as shown previously.
Removal of old seal material
The second tip is for Derrick38, who says it can be tough to remove old seal material from a compression chamber. Yes, it can! But I found that the patch removal tool that goes on my Thompson/Center Hawken ramrod is very good at scraping in those tight corners.
The patch removal tool on a Thompson/Center Hawken ramrod is great for picking old seal material out of the crevices of the compression chamber.
Sizing the new seal
The first thing to address is the piston seal. This one fit pretty tight in the spring tube of the rifle, so I decided to remove some material from the edges. There are a lot of ways to do this, and I chose the easiest one because I’m a guy who likes simple. I held the piston with seal in my right hand and a piece of 220-grain sandpaper in my left hand and proceeded to scrub off a tiny bit of the edge of the seal.
This is the way to make the new piston seal a trifle smaller.
You have to know when to stop. I just wanted the new seal to fit in the spring tube with slightly less resistance, which it did after a few minutes of work. Next, I cleaned the inside of the piston with denatured alcohol and Q-tips. It was caked with dried moly or tar that had to be removed. The 124 piston is very heavy for the power the gun develops, so heavy pellets should work pretty well.
Lube the compression chamber walls
I had cleaned out the compression chamber earlier, so now it was time to smear moly grease on the inside walls of the chamber. For that, I use a dowel with a paper towel folded over the end and held on with a rubber band. It allows me to accurately coat the inside of the cylinder.
Moly grease on a paper towel on the end of a dowel is the way to lube the inside of the compression chamber.
Lube the piston
Next, I lubricated the piston before putting it back in the gun. I put a stripe of moly grease around the front with the seal and another around the rear where the piston flares out.
A stripe of moly grease around the piston seal and another one at the rear of the steel piston will keep things slipping along.
The piston can now be inserted back into the spring tube, keeping the cocking slot aligned with the slot in the spring tube. When the front of the piston is in the tube, that’s the best time to lubricate the rear of the piston and the piston rod. Shove the piston into the tube with the new mainspring.
A stripe of moly grease around the rear of the steel piston keeps the metal-to-metal contact lubricated.
Install the sliding shoe/cocking link
Once the piston is inside the spring tube, the sliding “shoe” that connects the cocking link to the piston can be lubricated and installed. A wide spot in the spring tube slot accepts this shoe.
The shoe is lubricated with moly grease on both sides and dropped through the wide spot in the spring tube. It rides on a special bearing surface on the piston, so that was also moly-ed before installation.
Lube and install the mainspring
Next it was time to install the new mainspring. Before I did that, the spring got a liberal coating of black tar, the open gear lubricant that deadens vibration. I smear the front half of the spring first, then insert it into the piston and use it to hold the spring so I can lube the rear half.
Caution–here is where I screwed up!
What the picture shows is too much black tar being put on the mainspring. I didn’t know that until the job was finished and the gun back together, of course, but I now have a rifle shooting 7.9-grain Premiers at 670 f.p.s. instead of the approximately 840 f.p.s. I expected. I used too much because Jim Maccari said the Mongoose kit I selected was a loose fit and needed tar to calm the vibrations. I hate vibrations, so I went overboard. The fix will be to take the gun apart and remove a lot of the tar I applied.
This is too much black tar. I will have to remove a lot of it.
One thing about fitting a mainspring to a rifle. The tightest end of the spring always goes over the spring guide in the rear.
Lube the baseblock and pivot bolt
The FWB 124 has a baseblock bearing on just the right side. The left side is plain. I smeared moly grease on both sides and also on the pivot bolt before it was inserted.
Moly on both sides of the baseblock and on the pivot bolt will reduce the cocking effort to the minimum.
The trigger unit is now pushed back into the spring tube, keeping tension on the safety spring as you go. When the bolt hole lines up, the bolt is screwed in and the job is just about finished. Just put the action back in the stock and you’re done.
Mainspring compressor make this an easy job.
The tuned rifle cocks easily at just 23 lbs. Beeman used to advertise the cocking effort at 18 lbs., but all the 124s (about a dozen) I have tested were around 21-23 lbs. So, we’re in the ballpark. Of course, the velocity is low, but I’ll take care of that in the next report. I’ll also shoot the rifle for accuracy with open sights.
The trigger is one thing I never learned to adjust on a 124 and I used to think it was impossible, but I once owned Mrs. Beeman’s 124, which I named the Queen B. That trigger broke at less than a pound, so someone knows how to do the job. Just not me.
Irony at work
Of course, the new pliable breech seal was installed and the petrified “new” breech seal I had tried went back into the box with all the other ruined new parts. I find it incredibly ironic that the owner of this fine rifle had wanted to preserve it for all time and it didn’t last as well as a similar rifle used every day. I guess man plans and God laughs.