Idiots guide to classic airgun strips (pt 1)

[Phil Russell]

THE MIDLAND GUN COMPANY DEMON DELUXE (AND DEMON)

This rifle, serial No. 878, is a .22 Demon Deluxe and would date from the mid 1920s, I think. Overall it is in good condition although close inspection shows that it has had some refurbishment as there are signs of minor pitting to the action and the stock seems to have been re-varnished at some point. The engraving on the action; a feature that distinguishes the Deluxe from the standard Demon is in good condition and extends to all screws. The top of the barrel flat is stamped ‘The Midland Gun Co, Birmingham Made in England. A test fire showed a very smooth action but output was thought to be on the low side. The rifle dieseled badly with every shot including some smoke from the breech area. It was time to investigate further.
If you have ever stripped similar rifles e.g. pre-war Diana 27 then the format of the rifle will present no problems but there are a couple of things to note. I began by removing the barrel and cocking slide as a unit by removing the barrel pivot keeper screw and then the barrel pivot screw. The breech block was a bit loose in the cylinder jaws. It was possible to tighten this up by tightening the pivot screw but the keeper screw would not then fit. A shim washer under the pivot screw solved this … there was one washer there already. It would have been OK if I had just removed this single shim washer but I thought it best to keep a shim there.
The butt plate was next, two screws. Look for the stock retaining nut visible in the hole in the end of the stock. Just loosen it; mine took an 18mm af box spanner. Then back off the trigger adjusting screw a couple of turns and remove the two front trigger guard screws. Note that the rear guard screw passes through the action to screw into a small angular steel plate on top of the stock. Remove the screw and the guard. Now undo the stock retaining nut and remove the stock. I expected to find that the steel rod holding the stock had a hole drilled through it where it screws into the trigger block but mine only had a ‘half a hole’ as if the rod had snapped in half at this point sometime. I could have drilled another hole further back but left it ‘as is’.
Now remove the trigger. Remove pivot screw and remove the screw while holding the trigger blade. When the blade is free from the action, pivot it on the trigger spring and lift clear.
Turn attention to the cylinder. Clamp trigger block in a padded vice and unscrew cylinder. Preload is not excessive at about 35mm but present so take care. When unscrewed, remove spring and piston. It was clear why the action was so smooth … the inside was liberally coated in enough grease to service a London bus. And it looked like standard wheel bearing grease. The piston washer was, as expected, leather and was in excellent condition. There was some light scuffing on the piston rear which was removed. Everything was cleaned of the old grease. The spring looked OK, nice and straight and fitted the piston and guide well so it was not changed. It measured 34 coils, 239mm long, 3.03mm wire, 12.8mmid, 19mmod. I later found a picture of the parts on the Vintage Airgun Forum and the spring shown was a bit different at 38 coils. The Demon here had come to me with a spring marked 'Demon': 38 coils,2.73 wire, 18.6od.
The leaky breech seal was replaced with a new made leather one .. ½” od with a 5/16” inner hole x approx. 2mm thick.
Note that if you only want to access the spring and piston there is no need for a full strip. Simply remove the two front screws from the trigger guard and unscrew the trigger block, trigger and stock as a unit from the cylinder. To access the piston you will need to remove the barrel and cocking link or just the cocking link as well.
Reassembly is the reverse of the above. I used moly CV grease on the spring and piston. A light lubrication of the leather washer followed. I added a slip washer to the base of the piston and clamped the cylinder in a padded vice and offered up the trigger block in order to get them back together. I tried the reverse but found it difficult as the piston rod is a good fit in the spring guide and getting it aligned perfectly against the preload spring pressure was difficult. Somehow, clamping the cylinder made it easier. When doing this make sure the cocking slot in the piston lines up with the slot in the cylinder.
With the trigger block in place, replace trigger. Hold trigger and its spring together and add the end of the spring into the recess in the block. Swivel the trigger and feed it down against spring pressure until you can add a drift through the pivot hole to hold it all in place. Now feed the pivot screw through to replace the drift and secure the trigger. Make sure the trigger moves back and forth against spring pressure. Return the adjuster screw to its original position.
Add barrel and cocking link, ensuring any shims are present on the pivot screw and that it is possible to add the locking screw to lock the pivot.
Make sure that the stock securing rod is positioned correctly to allow the rear trigger guard screw to pass through it. Add the stock and its securing nut but do not tighten fully. Add trigger guard and the rear screw, making sure it passes through to locate in the angular plate on top of the stock. Just nip tight. Add the front guard screws. Tighten the stock securing nut then tighten the rear guard screw.
While doing this service I noted that all parts were stamped with the serial number 878, including the inside of the butt plate.
Add butt plate. Job done.
On testing I found that AAF were a loose fit and seated maybe 3mm into the breech. 5.6mm Marksman and 5.6mm Wasps (new version) seated higher. There was still some dieseling which I have put down to the leather piston washer being impregnated with oil etc. The action was a little noisier which I put down to the amount of grease I scooped out.
Performance came in at around 6 - 6.5 ft lbs excluding higher readings from obvious diesels.
However, the extra noise bothered me so I stripped the rifle again and replaced the mainspring with the 'spare' that had come with the rifle. There was maybe an extra 25mm preload which made fitting the spring more of an effort as the piston rod was a good fit in the spring guide and both had to be perfectly lined up against the preload pressure. But on completion, a test showed the previous noise had gone. Performance was the same but the rifle was much nicer to shoot. I shall leave it alone now.
Maybe these figures are still influenced by dieseling but I am happy. And now quite fond of the old girl.
Cheers, Phil