help identifying modder of this QB78, maker of 8-shot mag, etc?
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help identifying modder of this QB78, maker of 8-shot mag, etc?
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Topic: help identifying modder of this QB78, maker of 8-shot mag, etc? (Read 6208 times))
Gerard
Sharp Shooter
Posts: 702
Real Name: Gerard
help identifying modder of this QB78, maker of 8-shot mag, etc?
«
on:
June 25, 2015, 01:07:44 AM »
Hey all. I recently acquired a customized QB78 from a casual collector. He'd bought it from someone else and had no clue as to who did the build, had never even shot it, just one more thing in his collection until he sold it to me. The barrel is 14" long, and the bore WAY off to one side and counter-bored a few millimetres. Get the feeling it's a stock barrel but as I know next to nothing of this model that could be a silly thing to say. If it was chopped, someone did a terrible job of crowning it. I've pulled the barrel out and put it into my lathe, centred on the bore and turned it down to 1/2" for 1/2" back and re-crowned it, will be putting an air stripper on when I find the time to make one. Doing that with the bore so far off-centre would have resulted in blasting the stripper cone right out of there, it was that bad... at least 1.3mm off centre.
So I've got this 'pistol' which really isn't practical as a pistol, Crosman grip frame notwithstanding. I've added a simple aluminum tubular stock. Making an air stripper soon, and will eventually find a scope for it with some mounts to barely clear the tall 8-shot magazine. Also planning to mount a 13ci bottle under it with an rsterne-designed, rrdstarr-machined reverse drop block to screw that into and some sort of sturdy cylinder/bottle band. Should make a nifty compact carbine.
I have a couple of questions, asking here as it seems there is a healthy population of QB78 modders in this place. First a couple of detail snaps of the parts I'm asking about below:
1) What can anyone tell me about the black delrin/acetal 8-shot magazine and mount? My Google-fu has so far been weak through a number of searches, showing only a couple of results with nothing conclusive about who made these and whether they're still being made. I'm especially curious about why there seem to be extra holes in the aluminum rotor face and in the corners of the delrin frame. A cover? An auto-advancing mechanism with spring? Seems manual rotation is a bit primitive, though it works, and if it can be made to auto-advance I'd like to know how.
2) Anyone recognize the brass and copper cocking knob? I cut about 1/2" off the brass shaft as it was really hanging out there far, if that helps. Soldered the copper into place after doing that as the file-fit domed end on the brass was depending on friction and I don't want to lose the nice copper end. I've found one like it in a rather scanty ancient thread on the Yellow, where it seems perhaps the maker was a George Benson -
http://www.network54.com/Forum/113813/thread/1233010468/George+Benson%27s+Custom+Built+QB78+Pistol
- but an attempt to send him a PM via CAF brought no reply. If the builder can be found perhaps I could learn more about the guts of this thing, and the max fill pressure, stuff like that which is good to know and a shame to be lost during various trades and sales. From what I've dug into so far the build looks solid enough, though a single set screw and grip frame bolt seem to be the only things restraining the valve from moving backward away from air pressure... so that might need upgrading. These things really ought to come with little notebooks for future owners... Mine also has the brass stock attachment fitting milled out to receive the Crosman grip frame, which works well enough but was about 1.2mm sloppy side-to-side so I soldered in a couple of small copper shims to make it a snug fit, and trimmed the bottom face a bit on a slant so it's not squeezing down on the web of my hand.
3) Any links to noob QB78 tear-down/mod threads anyone has saved would be welcome. The forum's internal search engine is... well... you know. I'm pretty much in the dark as to how the guts are arranged. Familiar enough that I have no trouble tuning a 22xx just about any old way, and this QB is shooting very nicely for what I want to do with it (using the whole main tube as a low pressure plenum for the regulated bottle, as it shoots nicely at 850psi) but who knows, I may want/need to tweak hammer weight, spring preload/length, etc to fine tune things with the bottle setup.
Thanks in advance for any offered help. Here's a picture of what it's looking like overall so far. I'm keeping an eye out for a fairly compact 6x scope, nothing too fancy. Figure with the regulated Ninja tank it might make a halfway decent HFT rig. It came with some 'target' carved grips out of some maple, putting a MASSIVE thumb rest and bottom edge shelf (to hold up a really heavy pinky fingertip perhaps?) on the left side and leaving the right side very plain and low-profile. Odd. Like the carver wanted his thumb to be very comfortable resting there... I may re-carve them to suit, but more likely will order some YHZ grip panels from D&L as I really like those and they need only a bit of re-carving and finishing to suit my hand well. Anyone want to buy a weird grip?
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Canada
Augydogy
Shooter
Posts: 60
Re: help identifying modder of this QB78, maker of 8-shot mag, etc?
«
Reply #1 on:
June 26, 2015, 02:39:28 AM »
1 - The guy who made that particular hand indexed magazine went out of business about 5 yrs ago, "primitive" but effective.
2 - In 10+ years of dealing with this addiction, I mean hobby, I have had 3 shafts break on me and they were 2 brass and 1 copper, they all broke at the bolt insertion and had to use an ez-out. I stay away form anything but a steel shaft since then.
3 - you tube.
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Gerard
Sharp Shooter
Posts: 702
Real Name: Gerard
Re: help identifying modder of this QB78, maker of 8-shot mag, etc?
«
Reply #2 on:
June 26, 2015, 03:17:41 AM »
1) Ah, I see. Feared as much, so no upgrades to indexed rotation unless I invent the heck out of it. A lightweight clock spring mounted inside a face plate might do it, but then again might just make the thing try to feed two pellets at a time with the second jamming into the first which had dropped into the bore, causing difficulties feeding and bent skirts. Still, worth thinking about I guess. Maybe if I deepened the bearing detent to firm up the stop for each pellet...
2) I don't see that being a worry here. Two reasons. The amount of force needed to close the bolt is really, really minimal, hardly sufficient to bend let alone break the brass, which I've shortened, making for less leverage. And since the brass is held into the bolt via a set screw from the back end of the bolt, well, I don't see how an easy-out would ever be necessary. Just loosen the set screw and tip the thing to the right and a broken-off end should just drop right out of the hole, making it dead simple to make a new shaft of something firmer if necessary. But no, it's not going to break unless I do some stupid upgrade to the spring making it MUCH harder to close. And with ~20fpe being plenty for me I don't see that happening.
3) Yeah. I resort to YouTube a lot, but try to avoid spending too many hours watching noobs claiming to have all the answers spending a lot of their and my time explaining the obvious. Just asking in case anyone had specifically wonderful links to excellent tutorials, whether text, photo, or video. I'll keep looking.
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Canada
Gerard
Sharp Shooter
Posts: 702
Real Name: Gerard
Re: help identifying modder of this QB78, maker of 8-shot mag, etc?
«
Reply #3 on:
September 09, 2015, 12:26:52 AM »
Just to follow up a bit, I've managed to get the QB78 using quite a bit less air while still delivering 19.8fpe with JSB 18.13gr.
- Made a hammer debounce device which works wonderfully, so I expect my shot count will be quite high once I get the Ninja tank hooked up. The adapter isn't made yet but I've spent a bit of time exploring the innards and sorting everything out properly for my use.
- Reduced hammer weight about 15%. Shortened the hammer spring and added a bit of preload.
- Smoothed some rough edges so everything's slick inside.
- Removed a strange little X-form washer and steel tube from inside the valve and made a new valve poppet seal out of delrin, with a longer spring to push directly on the valve's front face.
- Drilled a bunch of holes up front in the valve body to increase flow.
- Made a delrin filler piece to reduce the main tube volume by about 50%, so it's just over rsterne's recommended 1cc per fpe as a plenum volume - about 22cc remaining, so less problematic towards the end of the Ninja bottle fill in terms of remaining volume in the main tube when off-regulator.
- Re-carved the dark rosewood grips from another airgun so they work nicely on this one - that 2260 will get the maple grips from this one after some re-carving.
- Epoxy painted the slip-on pipe stock, roasted it to harden. Going for the black-on-black look with this one. The aluminum dropped tank adapter will get the same treatment.
Won't bother with pics this time, but I'll revive the thread when I've got it all built and shooting. Thinking about a fixed 4x Leupold for this one, but might chicken out and get a cheaper scope to start with just to see how well it shoots before committing to better glass. Working on the innards wasn't so challenging once I got in there and figured everything out. A bit easier to work on than the 22xx series guns actually, seems to be built a bit more ruggedly, especially the great big breech screw.
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Canada
Kailua
GTA Senior Contributor
Posts: 3613
Real Name: Paul
Re: help identifying modder of this QB78, maker of 8-shot mag, etc?
«
Reply #4 on:
September 09, 2015, 03:29:55 AM »
Just for you general info there is a universal mag made by Rowan Engineering.
http://rowanengineering.com/products20.htm
Also this deals with air strippers but Mac1's idea of centering an air stripper should work with a LDC. Check out reply #18.
http://www.gatewaytoairguns.org/GTA/index.php?topic=96718.0
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Kailua (Oahu) Hawaii
Gerard
Sharp Shooter
Posts: 702
Real Name: Gerard
Re: help identifying modder of this QB78, maker of 8-shot mag, etc?
«
Reply #5 on:
September 09, 2015, 03:51:29 AM »
Thanks I guess. Though the airgun already has a magazine, so no need to get a different one. And I've turned the barrel down to centre it on the bore, actually forgot to list that - the other day I decided to cut the front 4" down to 13mm diameter and crown it better than my previous attempt, after figuring out a better way to mount it on my little lathe. Cut the length down to 13.5" and did a much tidier job of it this time. I'll be mounting a long brass stripper sometime soon over that reduced part of the barrel. Now that so much barrel is concentric to the bore it'll be no trouble at all aligning a very closely fitted adjustable stripper cone.
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Canada
aj.allen92
Shooter
Posts: 16
yes
Real Name: AJ
Re: help identifying modder of this QB78, maker of 8-shot mag, etc?
«
Reply #6 on:
December 14, 2015, 08:56:37 PM »
Could anyone tell me if the QB 78 repeating mags will work on a Benjamin discovery???
Any help would be much appreciated!
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mass
Gippeto
Sharp Shooter
Posts: 864
Re: help identifying modder of this QB78, maker of 8-shot mag, etc?
«
Reply #7 on:
December 14, 2015, 10:34:33 PM »
The RIM did....
http://www.airgunartisans.com/AAQBMags.htm
Al
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Alberta, Canada
Gerard
Sharp Shooter
Posts: 702
Real Name: Gerard
Re: help identifying modder of this QB78, maker of 8-shot mag, etc?
«
Reply #8 on:
December 14, 2015, 10:58:16 PM »
Quote from: Gippeto on December 14, 2015, 10:34:33 PM
The RIM did....
http://www.airgunartisans.com/AAQBMags.htm
Thanks for this! Somehow I couldn't find it, but this is the system on my QB78 and I'm happy to finally know its source.
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Canada
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help identifying modder of this QB78, maker of 8-shot mag, etc?