I posted a couple of pictures in the bullpup thread, but finally finished work on my QB57 so I'll post a proper thread for it. First off here's the ugly thing as it arrived, with lots of stuff on it I planned to get rid of long before I ordered the beast:

So I heated the muzzle brake and stuck it in a vise and wiggled it off. Turns out the reduced section of the muzzle end of the barrel has 6 splines swaged into it like long shallow teeth, designed to keep this brake from coming loose or turning. Makes sense, if you like that sort of thing. The wooden thing on the barrel bugged me so off that came. Plastic grip and trigger guard gone. Rear cylinder plastic cap too. Butt plate gone. All I wanted was the main cylinder with guts, the barrel, and to re-work the stock. Started with the stock, carving away the awfulness and leaving something I could stand, adding a simple maple grip:

I re-crowned the barrel and polished the breech end cone smooth, using my little TAIG lathe for these. Also turned down the barrel retaining flange (which was severely lop-sided - about twice as thick on one side as on the other) until it was actually round and concentric with the barrel. Brazed about a 4mm long piece stainless steel tube into the opening in the barrel retaining nut, building up bronze on the front side, as the hole for the barrel was a very loose fit. Opened out the stainless tube until the barrel could just get though without forcing it.


The cocking lever jumped out about 3mm from the cylinder when captured by the little catch, a very sloppy fit, so I dismantled that, filed the surfaces to prepare for brazing and brazed the ends of the two stamped arms together then brazed a 3mm thick piece of steel onto the tip, filing it to fit once cooled. The lever now takes a bit of a nudge to get it to lock, and same with opening, just a bit of a squeeze against the cylinder to enable pressing the release catch.

At the other end of the cocking lever I didn't like the sloppiness of the fit at all. A folded piece of steel with the two flanges not at all parallel to each other, some room for wiggling on the pin, and of course room for distortion in use over time. So I fitted a steel nut into the open space and brazed that into place. Used a sprung shim washer to take up the slack on the outside of the joint. Very acceptable snug fit now, just free to move.

Inside I didn't do much to the trigger/sear, as it's a bit of a loose jumble of parts and frankly scares me a little. If it ever breaks I'll fix it, until then I'll just give it the odd drop of oil and try not to think about it. I did straighten the connecting rod a little and drilled out the pin hole for the safety (didn't want a safety, especially not such a badly made one) and put in a steel bolt to replace it. This was big enough that it stops the trigger from going nearly so far forward, shortening the initial easy stroke of the trigger dramatically. It's still a long trigger pull but much more comfortable, and the final effort is around 2 pounds or a bit less.
I used a bar clamp for a spring vise, undoing the two bolts on the rear steel cap and gradually releasing tension. Needn't have worried as the factory preload was only about 2 inches, very mellow. The insides were a bit dirty and there were a few burrs so I cleaned that stuff up and re-lubricated lightly with white lithium grease. Actually tried a moly paste first, but it slowed things down too much, dropping JSB Heavy pellets into the mid-400's. With a bare minimum of lithium grease it's around 500fps with the same pellets. From the factory (I bought this one from Scopes & Ammo) it was dieseling quite badly, averaging around 540fps and jumping as high as the mid-600's for a little while.

That's when I decided to clean it out and re-lubricate, as I don't need nor want that sort of power, or NOISE, out of this little carbine. I turned the steel spring guide round and polished it - the swaged sheet steel guide was rather out of round and sharp edged. De-burred a lot of edges on the cylinder and cocking linkages and loading bay. Added about 14mm of shims to preload the mainspring, as there was a very brief but somewhat harsh twang in my ear, and after a couple of assemblies with different shims this seemed to minimize that noise. Still a harsh sound but no twang at all, just something more like a hammer blow on a heavy anvil resting in dirt. No ring, just whack!
I also made a brass trigger guard. Bedded the heavy steel rear cap and the front conical section of the receiver into the stock for about an inch each end with epoxy putty, leaving the cylinder itself free to vibrate as some experts advise. Wrapped the trigger linkage rod with a thin but stiff plastic sheet then soft foam before inserting it into the cut-out in the stock to help absorb some noise, as the thinned beech stock amplifies the piston noise considerably. I used a couple of rubbed-in coats of a linseed oil based varnish with a blue pigment powder mixed in. Absorbed quite differently into the maple grip, but I figure over time that'll darken with handling so I won't try to go further with colour there.
I made a PVC barrel shroud with a locating spacer at the muzzle to allow it to slip about 2cm fore-and-aft when assembling and dismantling the gun. I drilled and tapped through the 1.25" PVC for a 3/8" nylon bolt to capture it, as I didn't want the shroud falling off for transport and taking the muzzle spacer and barrel retaining nut with it. I reamed the rear of the PVC tube until it was a tight fit for the retaining nut, then epoxied that into place. Since Industry has used a twin-lead threading, the barrel nut actually spins on very fast. Oh, before any of this stuff I had to make a new indexing pin to fit the hole in the barrel, as I somehow dropped mine on my workshop floor on a day when I hadn't swept and never did get a proper look at that thing. The new one's a tight hammered fit, then filed until it just barely gets into the slot in the receiver. So the forestock (PVC shroud) is now an extended barrel nut. I just slip the rearmost 3" or barrel into the receiver, with the cocking lever loose so the breech seal isn't resisting the barrel, then spin the shroud into place and tighten it.
Lastly I made an aluminum block to fit onto the receiver and put my Fastfire III red dot sight at the right height for my eye. Fitted the top with 4 hardened pins to index the Burris sight and tapped for the 2 mounting bolts. Drilled through the block into the receiver for a countersunk stainless bolt in 10-32 thread. It's fairly high at 53mm from centre of bore to red dot, but nowhere near as high as the stock scope mount which when combined with the ~500fps velocity makes for some tricky trajectory guessing. 53mm I can cope with, largely thanks to Chairgun Pro and its zero optimization tool. From my initial indoor setup I'm seeing the potential for perhaps loonie sized groups at 20 metres (rested) so factoring in that size with Chairgun I can hold on zero anywhere from 8.4 to 24.3 metres and hit that sized circle. Of course I may re-learn how to shoot a spring-powered air rifle well like I did as a kid, but that'll take time. I'm ruined for springers really, love my PCP stuff too much... but I wanted to have a 'rifle' to go along with my several Webley spring pistols, sort of balancing out the independence from a pump side of the collection as a follow-up to my 2240 build -
http://www.airgunforum.ca/forums/topic65612.html.
So here's the finished project. Shroud's painted to more or less match the stock.



And here are my leftovers. Anyone want some unused QB57 parts?

Seems the case is a bit bulky with the way I've got it set up now, so I'll be thinking of how to carry the thing. A violin case would work, with the QB assembled, but it breaks down so nicely. I must have something around here to stow it in... or maybe trade a few old fiddle cases for a small trumpet case?


Finished specifications:
Overall length - 30" or 76cm
broken down - 19" or 48cm
weight - 6.28 pounds or 2.85kg
Shooter's impressions:
Using the cylinder to rest one's face isn't optimal. Hearing protection might be a good idea with this one. Holding it at arm's length and firing the noise is trivial, like any non-PAL springer, but the intensity when pressed close to the ear is bordering on painful. I was thinking of shrouding the cylinder with 1/4" thick neoprene foam. Still might do that. Or I could use leather. Might be easier to glue. I'll be keeping an eye out for a tidy solution to cover the spring and piston area, wrapping the cocking lever as well such that when closed the large void leaving the spring/piston area open to the world is closed. Neoprene or leather would both work if well fitted. Making this little thing quieter on my right ear would bump it up a big step in enjoyment. As it is the noise is too harsh sounding to shoot too many times in a row.
With the action bedded at the ends and using a reasonably heavy pellet the recoil isn't very significant. I find recoil more annoying with the slightly lighter Industry-branded wadcutter pellets supplied with it. Those actually seem quite well made, no visible seams and very even in appearance, with well formed skirts and heads. Maybe I can use the rest of those up in something else. I'll probably try some heavier JSB pellets through this some time. I get the impression something around 20 grains might be better with this length of barrel and power plant.
The synthetic seals on piston and breech are a somewhat hard urethane, perhaps in the 75 to 80 durometer range. Since I polished the breech taper on the barrel I probably won't see much degrading of the breech seal, but it's good to know there's a spares kit available for these and the mainspring from Scopes & Ammo. Archer sells sets of 6 of the breech seals but they're out of stock, and I've read somewhere that they're a bit weird about shipping to Canada, at least for some airgun parts. I get the impression overall that with a bit of oil now and then and maybe an overhaul every 10 tins of pellets this gun ought to last a very long time, provided the trigger holds up. I had considered making a new stock for it from scratch, but frankly the harshness of the firing cycle noise put me off so I used the existing wood, and now that's done I'm happy enough with the result to leave well enough alone. I'll get back to work on fiddles now...