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 Post subject: Tank block for QB78
PostPosted: Tue Apr 29, 2014 2:32 pm 
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Location: Burlington, Ontario
So how should I start this process of adding holes to the tank block. Looks different from the 79 block. I added some pics below. My plan is to cut the 78 main tube right at end of the screw on cap threads so I don't really have to modify the stock.

The block has a pin, one oring and no screws.
I have limited hand tools, drill etc. thanks for the help.
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 Post subject: Re: Tank block for QB78
PostPosted: Wed Apr 30, 2014 10:48 am 
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Posts: 262
Location: Markham , Ontario
This is not really a job for limited hand tools . You may want to contact DerekVinyard here on the
forum and see if he will do it for you. Magnumair also used to do a lot with the QB 7X 's but he had
his lathe and mill up for sale recently so he may not be working on them any more.
You may want to consider cutting the tube a little shorter than just taking the threads off . It doesn't have
to be that log to be efficient , and it will look and balance if it's shorter.


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 Post subject: Re: Tank block for QB78
PostPosted: Wed Apr 30, 2014 1:58 pm 
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Location: Coalmont BC
The QB79 block has the air passage near the bottom of the stub, just above the O-ring groove.... That is to leave room for the mounting screws (or you could use a shear pin) on the horizontal centerline of the tube.... It looks to me like that tank block has the air passage higher up, which may not leave room for the screws.... Whatever you do, don't put the screws as close to the end of the tube as they do on a QB79, they are too close, and need the additional support of the stock (which screws to the sides of the block) to provide a good safety margin....

Bob

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 Post subject: Re: Tank block for QB78
PostPosted: Wed Apr 30, 2014 2:32 pm 
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Location: Burlington, Ontario
Thanks guys. I've been getting help from my barbas who already converted his. Just double checking before i get started. Barbas929 was kind enough to send me spare parts from his 79/78 conversion but I don't like the 79 main tube being so short and screw holes very close to the end of the tube for the tank block.

I plan on screwing where my finger is pointing somewhere along the middle of the tubing so it's further back on the main tube. I will tap it for 8/32 tensile steel screws.

Image
Image


I plan on usin co2 only 9oz tanks and keeping it under 500 fps. I already ported the barrel to beech port, poly tube mod, removed piercing pin and filter. I might need to cut the hammer spring to reduce power and reduce co2 consumption.

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 Post subject: Re: Tank block for QB78
PostPosted: Wed Apr 30, 2014 2:47 pm 
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Location: Coalmont BC
If you keep the tapped holes shallow enough to not break through into the air passage (and leave enough metal to not fail) then two high-tensile 8-32 SCHSs should be fine.... I would set the heads down into the outer tube if possible to spread the load into the tube wall, but if there isn't enough room between the O-ring and the end of the tube for that, then you don't have to if you're just running CO2 or HPA with a 1.8K burst disc on the regulator.... Keep the holes as far from the end of the tube as possible and still get the O-ring to seal properly....

Bob

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 Post subject: Re: Tank block for QB78
PostPosted: Wed Apr 30, 2014 3:13 pm 
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Location: Rocky Mtn Hse Alberta
It appears that the hole for the gas is where your finger is pointing making that the thinnest section. I would venture you have the best luck at 90 and 270 degrees. Also do as Bob suggested stay away from the tube end as much as practicable.
A third screw at 0 degrees would be additional safety.

Walter...

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 Post subject: Re: Tank block for QB78
PostPosted: Thu May 01, 2014 2:58 am 
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I have to dig one out that I have! I think barbas929(Steve) gave me one when I bought a QB79 from him.
But I need the experts to confirm if it is for QB's or Crosman's?

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 Post subject: Re: Tank block for QB78
PostPosted: Thu May 01, 2014 7:11 am 
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rrdstarr wrote:
I have to dig one out that I have! I think barbas929(Steve) gave me one when I bought a QB79 from him.
But I need the experts to confirm if it is for QB's or Crosman's?


it will fit both!!

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 Post subject: Re: Tank block for QB78
PostPosted: Thu May 01, 2014 8:12 am 
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Location: Burlington, Ontario
Thanks for the tips so far. Steve I might be texting you this weekend bud lol.
I got the block from sniper. I will post some pics once I get time time to work on this.

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 Post subject: Re: Tank block for QB78
PostPosted: Thu May 01, 2014 3:08 pm 
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Location: Burlington, Ontario
Glad I did tried this today before hacking my 78. I tried to fit the block on a 79 tube but it is too large to fit the tube. Looks like bulk fill adapter might be the easiest option.

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