I have too many .22 QB78's

[Mr. Panther]

     I actually only have 2 of them, but because I din't realize I had ordered the same caliber again when I ordered the second one, I now have two of the same caliber. So my solution to the problem is to take one and do a build on it to use a bottle or co2 adapter . I lined up the parts to order. It's pretty straight forward, all I need is my hack saw and drill press and dremel.
     I already have done all the power mods on itso it should perform real good with HPA as it will have a larger pleneum to work with, as I am cutting it off as close to the end as I can to maximize tube length. Ascetics aren't an issue for me, as I only care about performance. Scratches and what not really don't bother me as it gives it charactor I think.
      Some thing just o tide me over till January or maybe next month when I can see about getting a AT44S in .25. I don't want to have to tinker with that gun so this new endevour with an old gun will give me my tinker fix LOL.

[Ribbonstone]

Have posted this before...but finding it is more work than reposting.


OK...there are some advantages to cutting a 78 tube over an already gas block fitted 79 tube if you do your worke carefully.


Old QB79:



1. The tube has "flats" where the screws go.  So the tube is actually thinner where the screws take up the stress load.  That's not a place I'd pick to be thinner...there is some measureable elongation.

2. The issue tube holes are a touch larger than they need to be.  That puts more stress on a smaller contact area (the round screw just touches a small section of the hole) and the web of metal between the screw hole and the end of the tube is smaller.

3.  Often the gas block is not all the way into the tube when aligned with the screw holes.  The one shown above has some slack.


Now if you do a good job on the 78 tube, will end up with full thickness walls, smaller passage hole though the tube, and a bit more metal from the screw hole to the end of the tube.
 (yeah...the differnece in strength isn't likely a "ship load"...but it's something.  Enough that my 78 converted tubes don't show that hole elongation).



SO to make the screw locations "hillbilly easy" (still need care, but can make it more simple):

 Lets assume you cut the tube (we'll get to length a bit later) so it has no threads (threads are weaker than un threaded sections).  Have make it as falt and even as possible and have debured it inside and out.

OK...I cut two strips of Al. can.
Pucned  them each with holes that were a tight fit to the mounting screws.
Ran a tight fitting allen wrench though the two holes in the Al. strips and though the  mounting screw hole in the gas block..
Taped them firmly to the gas block, pointing eveny backwards so they'd be along side the undrilled gas tube ("puckered" side "up").







OK...at this point I have a "jig".  have pre-located the holes with non stretch material, the Al. strips aren't going to move. 

Take out the alignment rod (an allen key in this case).
Slide the block into the tube FULLY (lets push it in all the way and get the max. depth we can).



Carefully center punch a little dimple in the center of each of the holes in the al. strip.

Remove the block from the tube and get the "jig" off.

You end up with this. Correct screw holes location and a little dimple to get the drill started on center.


Now the trick is to drill the holes as small as you can...just large enough for the screws to pass though, but as little "slack" as possible.  I'll go look up the drill size, but I know I experimented with the cut off secion of tube to find out just how small I could get away with.

Once they're drilled, deburr them on the inside or you'll slice o-rings in seating.

The screws are there JUST to hold the gas block in....no comprssive force needed or wanted.  Do not have to be bust-a-gut tigh (in fact, comprssing the tube out of round kind of defeats 0-ring sealing).

LENGTH:

Kind of up to you, but I generally shorten the tube to where I need to inlet the stock to fit around the gas block.  I also use stock screws and epoxy putty bed the block.  I like the support. The tank is a pretty long lever, and I'd rather it not stress the gas block mounting when knocked.

Also tend to use the issue 78 barrel band rather than a QB79 barrel band...mostly because inletting a square block is a lot easier than inletting a square block with a band around it.





YEah...that's extra long becasue of the brass on/off.  Really don't need it, I just got into the habit.  Does come in handy, as it reads output pressure (and these old ones include another busrt disck between the bottle and the tube).

[Mr. Panther]

     Thanks for the information. I already had most of this information and is why I intended to do this conversion. For me it is a way to enjoy HPA, Co2 bottled, or to use the light co2 paintball converter with one 123 gram cartridge, which is super light.this is just something for me to do till I get my cash for my AT44. I had an extra .22 QB78 I wasn't using and decided it would be fun to convert it.
     I looked at various article on it here on the forum, so wasn't going into it blind I hd already done the valve work ala Jason's build on his QB conversion, except I left the striker in it to facilitate the use of CO2 cartridges. it hits hard, and is a gas hog for sure. When I put an RV on it I should be able to fix that little "problem" of gas useage and be more effecient. the info you posted should help out any one else looking to do this so thanks Ribbon.
       

[Ribbonstone]

May as well go for it...winter isn't real kind to co2...more like HPA weather.

Back then, I did swap back and forth from co2 in summer to HPA in winter.  Only hunting I do is in winter and HPA is the choice.  In summer, the only critters to shoot are pest birds so co2 power works fine.  I just ended up with too many airguns and don't really need to swap power sources (just swap rifles).

But one thing about that brass on/off.  Makes for the easiest co2  bulk fills if you don't like the weight of a co2 tank (which are heavier than the HPA tank when full of co2).  Cool rifle and slightly warm tank.  Screw on the tank, keep the rifle pointed up, turn the on/off to "on" and give it a 1/2 a minute.  Then turn to "off" and unscrew the tank.  Done.

[Mr. Panther]

     Yeah Ribbon, I have one of the brass on/off valves on my .22 QB79 I converted to HPA. They are handy for sure. Great tip about using it for bulk fill by the way. I hadn't thought of using it that way.
      I think the double "lock down " of the gas block is really not needed, (only in my opinion). The tube would have to bend considerably I would imagine, to make the screws pop out of the gas block. I mean if it makes things seem safer to you to do it that way then by all means go ahead, LOL, but my self I would rather just put a  barrel band on it and secure that to the gas block. that way I wont have to inlet any thing on the stock, and will pick up a little more volume in the tube. Just a thought, I may be wrong but I will find out when I do this. If I have to shorten it up to fit in the stock then it is no big "retooling" job to accomplish it LOL. Worst case scenario is it is just a little more tinker time, and I will have enough of that this winter.
     I do have other PCP guns, (actually more than I need), so this is just a little project I wanted to do, that might end up on the classifieds later. Once again thanks for your input about this. . Have a great weekend.

[rsterne]

Too many .22 cal QB78's?... I have an easy solution.... send me one to try my twin 88 gr. HPA setup on....



Like I need another project?.... 

Bob

[Mr. Panther]

LOL Bob your inventiveness never ceases to amaze me.  That is a cool set up, it will be interesting to see what it looks like when you do it.