As Lakey wrote in his article about BSA history, Many guns in the past were assembled using "obsolete" parts to use up stocks of spares...ie. when an "improved" model was announced, there was a transition period where guns would have parts or features of both the new and replaced version (this happened with the Mk1 and Mk2 Airsporters as well).
Now basically, If you exclude the Military pattern and Juvenile pattern guns, there were only three sizes of action (by action in this case I mean air cylinder / barrel assy....Actually, being pedantic there are four if you include the "junior" (not to be confused with the "juvenile")...The "junior" is actually a cut down Light or Ladies model!
The names of these guns (especially the largest) changed slightly over the years, so let me keep it simple and concentrate on pre WW1 guns.
The four sizes were;
45.5 inches (sporting model), 43.25 inches (standard model), 39 inches (light/ladies model)...and finally, the "junior"...at 34.25 inches....this last model was actually a light model action with 2 inches chopped off the barrel, and a shorter stock...the air cylinder and all else were essentially a light model.
Anyway.....I came by a 43.25 size Improved model D that was in very poor condition, and that had muzzle damage and a ding in the cylinder...It sat at home destined to be broken for spares until I thought I would try and make my own version of a "junior".
As usual, I made it a bit harder for myself than I needed...I wanted to keep the original stampings and markings, and this obsession caused my some headaches!
First job was to strip down as normal, then separate the air cylinder from the barrel. This is secured by soft solder, and either a commercial heat gun or propane can be used, in conjunction with a strap wrench to separate the parts in moments.
The next job was to shorten the cylinder and lose the part which was dinged....this was simply parted off in a lathe, and a new internal thread cut...the end was then faced off until the cylinder screwed home against the breech in the correct orientation.If I had been taking more care here...the job would have been much easier (more on this aspect of the job later!).
Then I cut off the end of the barrel, and set this up in a lathe as it looked a bit "heavy" to my eyes...so I reduced the size all along, but maintained the taper.(lots of filing and emery cloth work wonders!) It was re-crowned at the new length of 15 .5 inches.
next...I wanted a shorter cocking lever, but wanted to keep the Lincoln patent stamps, so this meant cutting it into 5 pieces, removing the "side fences", then re-welding 3 of them to get the appearance I wanted;
You can see in the above photo that the cocking lever latch position in the barrel is now wrong!....so that was filled with weld carefully, and new dovetails cut for this, and for the fore sight.
With some careful hand finishing,I was quite pleased with the finished lever;
O.K...remember the cylinder....well it was longer than a light one!...so after some head scratching, I came up with using a light piston...with a modified 43" piston rod. The rod had to be shortened, and a new notch machined, as it needed to be in between the length of the two I had (because of not paying attention with the cylinder length...I was more concerned with retaining the rolled, impressed markings on the cylinder to look central, instead of thinking ahead to cocking lever ratios etc.)
Anyway, as luck would have it...the slightly longer cylinder gave an unexpected result when combined with a light model cocking arm...the extra swept volume has made it quite a potent little gun, it runs smoothly at 630 fps with hobbies!
Here is the gun next to a 1920's light model...the difference in cylinder length is not immediately obvious (it is 8mm longer);
And here it is showing a 43" action above, the same as I started with...you can now see the result of all the work changing the barrel profile...compare the diameters at the same distance from the breech....it took hours, but I think it paid off in the finished job.
Re-assembly was as for a normal gun, with the exception of using a bearing fit locktite to hold the cylinder to the barrel...I am 100% convinced that BSA would have used this method if these engineering adhesives had been available at the time...they are widely used in modern gun assembly, by the likes of Air Arms and others. Instead of a re-blue, I went for Birchwood "plum brown", which has proved very durable, and has made the whole thing appear to have a better look IMHO, than a bright, new finish.
I also had a spare BSA number 19 combination foresight at the time, so I treated the little fellow to an upgrade. The actual project was for my girlfriend, who is quite small, and she finds it much easier to handle than a Light model, as well as being a bit more powerful;
The stock is an un-modified 13.25" inch one from the same period (the shorter than normal one was suggested for prone shooting at the time, and was a factory option).
It was not done with any attempt to deceive, as it is different in size to any BSA ever made by the factory....although when shown to one very, very well known expert on BSA guns, he initially thought is was a genuine factory "junior" from around 1910! (the serial is the original that the gun left the factory with in 1910/12...No.32717.
So, there you go....a un-usable gun saved, but an original 43" Improved model D lost...did I do the right thing???...my missus thinks so...she loves it!