Started my QB78 reverse bottle build - Finished!

[BigTinBoat]

Maybe you already have one, but if not, grab a cross-slide vice for your drill press and you can have a "caveman mill" of sorts like what I was using for the longest time...still use it the odd time as long as high-precision isn't required.

Not yet, but on the list. Most run almost as much as the drill press itself.

[BigTinBoat]

Well I put the valve back into the gun and it's sitting charged with 1000psi to check for leaks.

Will this is sitting I decided to start work on my stock. Picked up a new "2nd" stock from Brett over on the yellow cheap and the work has begun. I wanted a "pistol" grip on my stock and Since I'm left handed a target stock would have done me no good.

So here is my stock as it has progressed today.

As received compared to my "Deluxe". Notice how "flat" the grip is, not good

After removing some wood

Getting the "angle" on the top

First layer of Bondo - done with a gloved hand as learned on google

2nd layer of Bondo

Started shaping (needs more filling). Much easier to reach the trigger now. Will be spray painting with Bed Liner once done. As you can see the gauge is even with my tape mark after 2 hrs so hopefully no leaks

Just a little more "faring" left to do

[BigTinBoat]

Well I put the parts all back together with the 13ci bottle set at 1300Psi. The 13ci fits a bit better then the 17ci.

I turned the RVA in a little at a time until the pellet shot out and it was 425fps. I was just using my cheapest pellets which are the Winchester 9.8 domes. Kept turning the RVA in a little at a time and the velocity climbed all the way up to a top of 975fps. That's 20.69FPE. I'm pleased.
Once I get the stock all cut and painted I'll check my efficiency. Put a piece of toilet paper over the breech and when shooting it didn't move. The Crosman breech seal must be working.

With nothing on the barrel it does get a bit loud at those speeds.

[nervoustrigger]

Nice work, sir!  It feels good, doesn't it?

20fpe in .177 will give you some nice flat shooting.  If your barrel is like those I've worked on, you're going to want some JSB and Air Arms in 10.3gr and 8.4gr.  I hope to see you showing off some groups in the near future!

[BigTinBoat]

Nice work, sir!  It feels good, doesn't it?

20fpe in .177 will give you some nice flat shooting.  If your barrel is like those I've worked on, you're going to want some JSB and Air Arms in 10.3gr and 8.4gr.  I hope to see you showing off some groups in the near future!

Thanks Jason - feels great, and I couldn't have done it without ya - I have a bunch of the 8.4 JSB's as my 1720T loves them. Just need to get a couple packs of the 10.3's

[BigTinBoat]

Work has kinda slowed by progress, but I'm almost there. I epoxied a 3/8" alum bolt to the end of my bottle and once the stock is dried over night I will drill it so that the bolt will go into the hole and my bottle will be supported at both the bottom and the top.

Here is what my stock looks like now:

Compared to what it started as: (a $10 "Standard" 2nd)

[Geoff]

looks nice man.   cant wait to see it all together

[nervoustrigger]

+1 on Geoffrey's comment.  I'm looking forward to seeing your creation all put together...almost as much as I want to see groups!

[BigTinBoat]

looks nice man.   cant wait to see it all together

+1 on Geoffrey's comment.  I'm looking forward to seeing your creation all put together...almost as much as I want to see groups!

Thanks - you and me both - but the can says don't put anything in truck bed for 72hrs so I'm going to let it hang that long to cure. Plus I will be tied up with work stuff (man I can wait till October for retirement) at least thru Wednesday.

While I was waiting today I did get a chance to go thru my flea market pick-up
http://www.gatewaytoairguns.org/GTA/index.php?topic=82190.

[BigTinBoat]

No time yet to shoot, but I did get it all together and it's holding 1300psi.

The bottom of bottle is supported by an alum rod that I epoxied to the bottle bottom. It fits into a hole drilled into stock. Doesn't move at all

Here it is all together. Just have my LDC to add after I test fire to see how it groups

[HappyHunter]

That looks fantastic, Rob!... ....well done, sir!

I may have missed it, but how did you cut your radius in the stock for the bottle? I know when I did it to my AR2078 there was a whole bunch of ol' fashion elbow grease involved! Just wondering if you found an easier way... .

I have a pretty fair size set of meat hooks and find that the 13 ci bottle makes for a really comfortable forestock. Looks great the way it is, but was just thinking you could always paint the bottle (at least the "fat" section) with bed liner to match the rest of stock for a little more grip.

Now you just gotta get some range time in with your new baby...you've certainly earned it!

[BigTinBoat]

That looks fantastic, Rob!... ....well done, sir!

I may have missed it, but how did you cut your radius in the stock for the bottle? I know when I did it to my AR2078 there was a whole bunch of ol' fashion elbow grease involved! Just wondering if you found an easier way... .

Thanks Todd
The radius wasn't easy. I first cut the main chunk off square. Then I put a ball shaped "cutter" in the drill press and put the stock under it. I had a line drawn about where it should be. Lots of cutting then checking with the bottle. Just left the press retracted and held the stock up under it and put pressure on it.

I have a pretty fair size set of meat hooks and find that the 13 ci bottle makes for a really comfortable forestock. Looks great the way it is, but was just thinking you could always paint the bottle (at least the "fat" section) with bed liner to match the rest of stock for a little more grip.

I thought about doing the bottle, but wanted to see what it looked like first. Figured it would be easier to add then take back off. I will likely wind up doing it in the future. The ASA on/off makes it nice that I can just turn it off, shoot the air air of tube and remove the bottle without draining the whole bottle.

Now you just gotta get some range time in with your new baby...you've certainly earned it!

Yep - just got like 10 other projects going on and it's snowing here now. Hopefully by the weekend, but it will only be indoors at 10m

[BigTinBoat]

Well my curiosity was killing me. Made the wife some Venison (backstrap) stirfry and then I was able to head back into the basement.



Set everything up and got my Winny 9.8g domes.

Shot the gun as I had it with just a tiny bit of preload - 222FPS

Turned the adjuster in 1 turn - 382FPS

+1 Turn - 564FPS

+1 Turn - 688FPS

+1 Turn - 807FPS

+1 Turn - 912FPS

+1 Turn - 939FPS (getting loud and can hear the wasted air)

+1 Turn - 950FPS (getting even louder)

Decide to throw in a 7.0 RWS and see what happens


So I back it off 2 turns and get out the JSB 8.44's - 5 shots between 944 and 954
I know this is only 10M, but it's shooting like my 1720T at this distance. This group is not cherry picked, it's the ONLY group I shot. Now I can relax and make my LDC while this weather clears. Looks like this gun is going to be a shooter. I think I won the Chinese barrel lottery.


On a side note I want to thank rsterne, Ribbonstone, nervoustrigger, HappyHunter, John B and rloftus (I think that's everybody)

Without the QB knowledge and experience (and HPA in general) you guys have brought to this forum I would not have gotten the nerve to try something like this.

Thanks Again!

[nervoustrigger]

Fine shooting sir, and congratulations on a job well done!

I see in your future the need to stretch out to greater and greater distances.  And it's so much fun

You got a good barrel, indeed, and your accurizing steps are paying immediate dividends.

[rloftus]

Great job Rob!  The gun looks very nice.  Hope you enjoy yours as much as I do mine!

Roger

[Big Tim]

Wow! Really, really nice job!

[BigTinBoat]

Well I had put one of those little spring plungers in my trigger housing but it really didn't give me a distinct stage from 1st to 2nd so I took it back apart and "fixed" it. I chucked up a 8/32 bolt in my drill and filed down the threads where it would slide inside the hole in the trigger housing and made myself one of those 2 stage trigger mods that gets sold on the internet for like $22. While I was at it I filed the blade of my trigger (where it contacts the sear) to a "blade" to reduce friction. I LOVE this trigger now. Breaks like glass!

While I was at it I decided to paint my bottle with bedliner to match the stock. I really like the look now. And it's finished. Can't wait for the weather to break so I can get outside. In the basement of sand bags it puts JSB 8.44's into a single hole at 815fps. Turn my RVA in 2 turns and it's spitting them at about 980FPS. It's also my quietest gun.


I'm real satisfied.

[aPpYe]

HappyHunter, is this a QB78???  This pic is what prompted me to actually join this forum!  What stock is that?  Where does the gun balance?  Myself, I am wanting to build something like this, but with aperture sights and maybe without the shroud.  I might also try to bring the bottle up a bit closer to the tube as well.

[Sfttailrdr46]

  I have to say this and it is not intended as anything but a compliment you guys that are mod -aholics are incredibly inventive. It never ceases to amaze me what you guys can accomplish with a little imagination and some spare time

[rsterne]

aPpYe.... That is a Crosman, likely a 2260 tube, 2240/50 grip frame and skeleton stock.... modded to accept a regulated bottle.... If you attempt something like that, make sure the regulator has a 1.8K burst disc on the output side, which will restrict the setpoint pressure to about 1500 psi max.... Even then, it would be a good idea to upgrade the valve screws to 10-32 in case the regulator fails and dumps 3000 psi into the gun.... A Disco valve with all 3 mounting screws installed is the minimum needed for safety.... and I'm not particularly fond of the bottle being hung so far below the main tube, and in particular what looks like a pipe nipple between the tank and elbow.... If all the fittings are not rated for the working pressure, with a safety factor to allow for a regulator failure (ie 3000 psi), I wouldn't even fill it....

Bob