Idiots guide to classic airgun strips (pt 1)

[Phil Russell]

Gem Style, no maker’s name. Most likely a model 13A from Eisenwerke Gaggenau (Iron Works, Gaggenau)
No. 57748 inside breech with numbers 748 or just 48 on other major parts. This rifle, .177, had been languishing in a cupboard for a long time. No makers name: overall 34” with 17.5” barrel, round but with a top flat. Barrel latch operated by a sprung lever on top of cylinder which, when pressed, allows the barrel to open.
Full of anticipation I tried a test shot; pellet only went about 1” down the, smooth, bore. Time for a service. I removed the screw bolt at the rear of the action near the front of the half stock. This pulls the sides of the cylinder together to nip on the thread of the cylinder / stock plug, holding the stock in place. Removing the bolt allowed the complete stock to unscrew from the cylinder; this gives access to the mainspring. There was a fair amount of preload, maybe 2”. When new I suspect the spring to be 8.25”, 37 coils of 2mm wire 15mm od. The rifle’s spring was about 1” shorter. Remove trigger guard /cocking lever by tapping out the pin at the front of the guard. Guard can now be removed to the rear of the action, bringing the piston with it. My trigger guard pin was bent so a new one was made from a suitable HSS drill shank. The piston rattled its way out of the cylinder. I was surprised to see a huge sealing washer about 9.5mm thick on the end of the piston. There was a steel washer secured by a peened over end to the central rivet rod, 8mm approx. diameter. There was no visible means of removal so I concluded the unit had been ‘rivetted’ into place. As I wanted to get the rifle working, I decided that a new washer would have to be fitted even if this meant sacrificing some of the old central rod/rivet. I decided not to attempt driving the rivet/rod out so removed the peened end to allow the end steel washer and piston seal to be removed. A new leather washer was fitted by tapping the end of the original rivet with a 4mm thread and screwing the new washer unit into place with a delrin spacer to give the same length of piston washer unit as original.
A new leather breech seal was fitted, 10.5mm od x 2.4mm thick with a 3.5mm hole punched in the centre. It is possible that the old seal could have been saved by a good soak in neatsfoot but I decided to do a new one.
The barrel release catch was a bit loose on its mount on top of the cylinder but after a failed attempt to tap out the pivot pin I decided to leave it alone: the pin was very firmly stuck and the catch worked OK as it was. Similarly I did not remove the trigger parts as I saw no need to. All are retained by pins. The trigger can be adjusted by a small screw on the trigger blade that adjusts sear engagement. It was loose so I put a drop of mild Loctite on it. I intended to remove the stock from its steel end plate but only one screw undid so I left it alone.
I lubricated and reassembled the rifle with the original spring and was pleased to see c. 340fps with Geco wadcutters and c. 320fps with AA Field. To satisfy curiosity I removed this original spring and tried a spring of the same specification that was about 1” longer. It made no difference other than being harder to fit. So I put the original one back.
All I all it was great fun despite the piston washer surprising me. I wonder if all gem style rifles are like this?
Cheers, Phil