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Calling all QB78 gurus!
https://www.airgunforum.ca/forums/topic72230.html
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Author:  lleader [ Fri Apr 22, 2016 9:56 pm ]
Post subject:  Calling all QB78 gurus!

A while ago ago I purchased a used QB78D (.22). One of it's former owners got overenthusiastic with enlarging the transfer port hole in the barrel, with the result that it is difficult to load pellets without them hanging up on the hole. Wadcutters, which I prefer to shoot, are almost impossible - with round nose not a whole lot better. If you try to force the wadcutters the head on them will fold back at the waist. I'm tired of fighting with this.

My question: is there any way to address this without replacing the barrel? I haven't disassembled the gun yet to examine things in detail but I thought I'd access the combined knowledge of the group for advice. A thought that has crossed my mind is perhaps a custom made TP seal that extends up into the barrel and then contoured to match the bore diameter.

Barring the ability to fix this I guess I'd be in the market for an untouched .22 barrel... :wink:

Lon

Author:  Edmonton<500 [ Fri Apr 22, 2016 10:00 pm ]
Post subject:  Re: Calling all QB78 gurus!

http://www.airgunforum.ca/forums/topic72224.html

Author:  lleader [ Fri Apr 22, 2016 10:02 pm ]
Post subject:  Re: Calling all QB78 gurus!

Edmonton<500 wrote:

Way ahead of you. Already contacted Steve but the barrel(s) are sold. Thanks for the pointer, though.

Author:  vAgRaNt [ Fri Apr 22, 2016 10:30 pm ]
Post subject:  Re: Calling all QB78 gurus!

If you could get one of the lathe enabled members to cut a delrin, or aluminium TP, with a little extra meat on the end inserted into the barrel, you
could "massage" it to fit and provide the missing support your looking for. . . Certainly not impossible, but a fair bit of massage and custom fitting. . . .

A .22 barrel shouldn't be too hard to come by, it's the .177's that are harder to find. . . I've got a couple .22 QB barrels, but they aren't "D"s . . . Requires a different barrel band . . . 14vs15mm IIRC.

If you aren't able to find one local to you, lemme know by PM, and we'll figure something out. . . . :wink:

Author:  Gippeto [ Fri Apr 22, 2016 10:35 pm ]
Post subject:  Re: Calling all QB78 gurus!

If you consider it scrap as it is....and not knowing what you have for tools....

Bit of a long shot...could try and epoxy a piece of brass tubing into the hole...trim to fit and clean it up in the chamber...

With machine tools...cut the breech end off and re-do it.

Al

Author:  DerekVinyard [ Fri Apr 22, 2016 10:44 pm ]
Post subject:  Re: Calling all QB78 gurus!

The barrel could be shortened, machined again complete with a new transfer port...
Epoxy filled and redrilled transfer port would also keep the pellet from falling in with no safety issues.

Both options as already mentioned are good... But the cost of a 22 barrel isn't high, I would rather buy one than spend the time machining one (and I have the tools)...

Author:  lleader [ Fri Apr 22, 2016 11:12 pm ]
Post subject:  Re: Calling all QB78 gurus!

Good ideas here guys!. Didn't know about the difference between 78 and 78D barrel diameters. My tool selection is limited to a small drill press and a Dremel. I figured any 'fix' would involve reworking whatever protruded into the barrel which seems doable to me with the Dremel. I also have JB Weld which claims to be machinable. I am presently awaiting a o-ring kit to arrive and when it gets here I will take things apart and definitely try a few things out.

If anything else comes to mind, please enlighten me!

Lon

Author:  vAgRaNt [ Fri Apr 22, 2016 11:33 pm ]
Post subject:  Re: Calling all QB78 gurus!

lleader wrote:
. . . . a small drill press and a Dremel. . .

That, and some determination, and I think you're golden!

As suggested by DerekVinyard though, do you really want to? :lol:

A big part of why I enjoy this hobby, is the "shadetreeairgunsmithing". There's a lot of pride in accomplishing something of this nature.

Worst case scenario; you buy a new barrel and TP. As long as your proposed "fix" doesn't make any other part of the gun worse, the
worst you could accomplish is to freshen your drillpress and dremel skills, waste a few hours, and create a small pile of swarf, then
order/acquire that new barrel and shoot other guns till the pieces arrive. . . . Conversely, you could fix this pipe, so it loads nicer than it ever did new. . .

So; what'chya gonna do? :popcorn:

Author:  jezX [ Sat Apr 23, 2016 5:38 am ]
Post subject:  Re: Calling all QB78 gurus!

just turn the gun up side down when putting the bolt forward the last bit ... easy fix .
or id go with soldier , just clean the inside of the port hole well put a lil flux only on and stick a dowel or plug in the barrel .
then soldier it from the bottom on the muzzel side of the port hole ,it should stick well enough .

Author:  paddyfritz [ Sat Apr 23, 2016 6:54 am ]
Post subject:  Re: Calling all QB78 gurus!

Cheap and easy way, fill the hole with JB weld and bore it out to the size you need. Poly tubing would be good (ice maker line).

Author:  vAgRaNt [ Thu May 05, 2016 11:58 pm ]
Post subject:  Re: Calling all QB78 gurus!

Update Request: sorta curious how this story ended. . .

Author:  lleader [ Fri May 06, 2016 1:57 am ]
Post subject:  Re: Calling all QB78 gurus!

vAgRaNt wrote:
Update Request: sorta curious how this story ended. . .

Well, it hasn't ended yet. :lol:

I had an o-ring kit coming (thanks Buster95) because I didn't want to take the gun apart without them because from what I read I expected to rip the barrel o-rings taking it out. Then badshot read this thread and offered me a new 'D' barrel for a good price, so I bought that. The o-rings arrived before the new barrel did so I took the gun apart. Once I had the barrel out I played around with 'loading' pellets into it with a small wooden dowel. I soon discovered that the wadcutters were hanging up before they even got to the transfer port. Just about half a pellets length inside the barrel the barrel necks down slightly in diameter as it transitions from the loading tray diameter to the actual barrel diameter. I could have seen this without taking the gun apart but I was just ASSuming my problem was the transfer port. Anyway, the change in diameter was a sharp ridge and when the flat nosed pellet ran up against this it hung up seriously. If you attempted to force it it bent the head back. Especially the Miesterkugelns - man are they soft, and the back hole in them runs deep up behind the neck.

Then two things happened. On the same day, on the same postal delivery, the new barrel AND a Benjamin Classic .22 I had bought (from BC,thanks stic7) arrived. What do I play with first, huh? What? What? Well, I did a quick look at the new barrel and easily noted that the diameter transition zone that was a ridge in the old barrel was a nice tapered bevel in the new barrel. Pushed a coupe of wadcutters over it and no hangups. So I know what I have to clean up on the old barrel. There MAY still be slight problem with the transfer port on the old barrel, but the siren call of the new Benji was too loud to be ignored any longer. It is my first springer (I always said I wouldn't buy one...) and there is a lot to take in. But I will be getting back to the barrel, hopefully soon. (It also doesn't help that I am getting beat over the head with the Honey-Do list... :cry: )

Lon

Author:  vAgRaNt [ Fri May 06, 2016 11:11 pm ]
Post subject:  Re: Calling all QB78 gurus!

So; your original barrel is fixable, and you got a new barrel, and a new gun. . . Some guys have all the luck!

:lol:

Author:  lleader [ Fri May 06, 2016 11:41 pm ]
Post subject:  Re: Calling all QB78 gurus!

vAgRaNt wrote:
So; your original barrel is fixable, and you got a new barrel, and a new gun. . . Some guys have all the luck!

:lol:

You win some, you lose the rest. :wink:

I figure you might be interested in seeing the problem. Here's a pic. (Should have cleaned some of the lint off first...)
Image

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