Started my QB78 reverse bottle build - Finished!

[BigTinBoat]

Well I didn't get too far, but I wanted to start with the "easy" stuff first. I drilled and tapped the end cap for a 1/8"NPT fitting. Put it together and I think I have a slow leak at the gauge. I put my bottle that reg is set at 1050psi and the velocity with 9.8 pellets went from 520fps on CO2 (was about 65deg) to 650fps on the HPA. (5.9FPE to 9.2FPE) The bottle I plan to use is set at 1350psi, but just wanted to see what the lower pressure would do. I turned the bottle off and will let it sit a couple hrs to see if pressure goes done.
Can't wait to get inside it. Of course now my Christmas vacation is over and work will get in the way just a bit.

Just in case anyone is wondering - yes that is a brass nipple, but it is a Hoke Hex with a working pressure of 7100PSI

[Yarp]

Looking good.
Those valves occasionally leak as well. Is this its first use?

[nervoustrigger]

Best wishes for a successful build.  At 1350psi, once you get the airflow opened up, you shouldn't have any problem getting heavy .177 pellets going as fast as they have any business going

Do you have plans for accurizing the barrel?  In my experience, the QB barrels are stellar after some cleanup and breakin time.

[BigTinBoat]

Looking good.
Those valves occasionally leak as well. Is this its first use?

Yes - bought it from FD and shot the 2 carts that Mike put in it that's all. I thought I heard some air around the gauge but I just checked it after 90 mins and pressure seems to be holding at 1050psi. (After pressurizing I turned the valve back off so if there is a leak the bottle won't drain. Will see what it looks like in the morning before I go to work.

Best wishes for a successful build.  At 1350psi, once you get the airflow opened up, you shouldn't have any problem getting heavy .177 pellets going as fast as they have any business going

Thanks - I figured as much. Been reading a bunch of old posts from the expert converters, yours included. I like the option of an RVA like HappyHunter did to go from like 9fpe to 16fpe with just the change of a screw.

Do you have plans for accurizing the barrel?  In my experience, the QB barrels are stellar after some cleanup and breakin time.

Yes - plan to clean up TP and leade. Recrown and then polish bore with mothers to a mirror shine inside. I was shooting JSB's into a single hole at 10m in basement on the CO2.

[nervoustrigger]

I like the option of an RVA like HappyHunter did to go from like 9fpe to 16fpe with just the change of a screw.

Yep, an RVA sure is nice for tuning, no doubt.  ES tends to go up when backing off the power a lot but it can be perfectly acceptable considering the usual reason is for shooting at close range.  A few weeks ago I completed a .22 conversion for a buddy and dialed it down over half way to about 13fpe for a suburban squirrel hunt.  It went 6 for 6 that day at ranges under 30 yards and was just silly quiet in doing so 

Yes - plan to clean up TP and leade. Recrown and then polish bore with mothers to a mirror shine inside. I was shooting JSB's into a single hole at 10m in basement on the CO2.

Beautiful!  That sounds just right 

[UCChris]

This looks killer! I haven't forgotten what we discussed Jason. Looking forward to this fall!

[BigTinBoat]

Well 3 hrs later and still same pressure. I guess what I thought I heard wasn't really air or it would be down some by now. Hopefully in the AM it will still be the same.

  It went 6 for 6 that day at ranges under 30 yards and was just silly quiet in doing so 

Hopefully with the information you sent me I can make mine just as quiet at 16FPE.

[HappyHunter]

You're off to a good start, Rob!

Looking forward to the rest of your build and eventual range report...keep at 'er!

[BigTinBoat]

You're off to a good start, Rob!

Thanks Todd - can only hope it comes out performing close to yours.

Well it looks like the gauge is leaking, but I think it is the cheapie ASA. The gauge is not quite "tight" but it won't go in any further or the threads will hit the plunger that comes down and opens the pin valve. Going to order a CP or Empire that they use on PB markers. Ebay has then for like $12-14.
Didn't get too far after work. I did dis-assemble the entire gun and I converted the hollow bolt probe to an extended one and I cut the o-ring slot a bit so that I can get an #003 o-ring on it like the crosman's use. Just need to determine how long to make the probe

[PakProtector]

that bottle is one heck of a lever to hang off fittings like that.
cheers,
Douglas

[BigTinBoat]

that bottle is one heck of a lever to hang off fittings like that.
cheers,
Douglas

It won't be just "hanging". Plan to support the rear of bottle with something like this


From this build:
http://www.gatewaytoairguns.org/GTA/index.php?topic=60375.0

[HappyHunter]

Thanks Todd - can only hope it comes out performing close to yours.

Trust me, mine is nothing too special at all...Nervoustrigger is "da Man" when it comes to tinkerin' with the QB/AR series!

Well it looks like the gauge is leaking, but I think it is the cheapie ASA.

Just guessing here, but maybe try putting a few more wraps of teflon tape on the gauge threads to see if that helps?

Some of those ASA on/off adapters can be troublesome...I've had a couple that leaked pretty good when you were about half way between open and closed (not that you would ever run it at "half way", but still...). No problem when it was either wide open or shut right off, though...

Before I found a fellow to make me some reverse tank blocks, I had the same configuration as you on my 2260 (i.e- pipe nipples/elbows) and I too was a little leery about the "hanging" bottle so made a bracket to hold rear of bottle using (at that time) only "cave-man" tools. Certainly wasn't going to win any beauty contest with it , but it served the purpose at the time...nice and rigid.

Your solution will be much more elegant than mine was, but this is what I did:




Nice work on the bolt probe, btw!

[BigTinBoat]

Thanks Todd - you know I've seen that tank bracket before on the net.

I like the reverse bottle as I feel the bottle being supported by the "plumbing" in front, and a bracket in the back is much "safer" then just the ASA tank block "screwed" to the tube.

[BigTinBoat]

Well I got the barrel all cleaned out and a few mods done. Working 10am-6pm sure cuts into my time at home after work. Working 6am-2pm was perfect.

Anyway I wound up picking up a drill press at TSC for $74 so now I'm in business.

Doesn't look pretty , but I got the valve cut out and a seat drilled inside for the longer spring.

Polished up the valve stem and ground a spring seat in the end of it

Drilled my hammer for the reverse cocking mod. Not sure if I could have done this w/o the drill press

[BigTinBoat]

End cap drilled and tapped 10-32 for my RVA. Drill press made this A LOT easier

[nervoustrigger]

Hey Rob, you're coming along nicely!  She'll breathe a lot easier now with the ol' sinuses opened up.

So drilling the hammer was fun, huh?    How many drill bits did you burn up before you broke through the case hardening?  Or did you know to grind a dimple into it first?

Tapping the end cap is a little tedious, too.  Here's a tip now that you're done with it, haha!  I drill it one numbered bit larger than the normal tap drill size (based on ~75% thread engagement).  The part is so thick that you end up with so many threads to carry what is a miniscule axial load of the hammer spring, no need for so much engagement and it makes hand tapping less of a chore.

I'm looking forward to seeing your results!  If I'm keeping track, you're pretty close to being ready to reassemble except for the barrel work.

[BigTinBoat]

Hey Rob, you're coming along nicely!  She'll breathe a lot easier now with the ol' sinuses opened up.

So drilling the hammer was fun, huh?    How many drill bits did you burn up before you broke through the case hardening?  Or did you know to grind a dimple into it first?

Tapping the end cap is a little tedious, too.  Here's a tip now that you're done with it, haha!  I drill it one numbered bit larger than the normal tap drill size (based on ~75% thread engagement).  The part is so thick that you end up with so many threads to carry what is a miniscule axial load of the hammer spring, no need for so much engagement and it makes hand tapping less of a chore.

I'm looking forward to seeing your results!  If I'm keeping track, you're pretty close to being ready to reassemble except for the barrel work.

Thanks Jason -

Just one industrial quality bit. I took the 4" grinder and made just a tiny flat, you can just barely see it in the pic. I just kept putting real light pressure on the bit and as soon as I felt it getting close to hot I stopped for like 15min to cool down.

I had thought about using the next size up, but figured I shouldn't cut corners. In hindsight I could have just drilled it 1/2" way thru with like a 1/4" bit and only tapped 1/2" thickness. I think that would have been the easiest way. Another thought I had was to rotate the end cap 90deg and then drill and tap top and bottom with 10-32 (like Crosman is) and put the RVA thru the center. Just didn't know how the top of breech would look with a screw up top and I have no luck using cold blue so didn't want to mess that up.

Just waiting for the spring to be delivered, and some time off to get it back together. I think I have everything else de-burred, cleaned and polished.

[Ribbonstone]

Like the idea of adding support to the bottle either by clamping to the air tube or by using the stock for some support.  That’s a lot of weight focused on that threaded tubing when the gun is dropped or bumped hard. 

Am more of a forward tank guy as I like the front heavy feel, but even with those large diameter blocks/fittings, do take the time to inlet for the tank block, use the screws, and bed them to the stock for support. 

[BigTinBoat]

My trigger and sear is all polished up "mirror like" - 320 then 1200 then 2000 then Mothers Polish

[HappyHunter]

Lookin' really good, Rob! Getting close to "trigger time"soon...

Amazing how much easier things can be done even with a simple drill press, huh? Now you just have to save up for a small lathe and there will be no holding you back!

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. Those slots that you cut in your valve for example?...SOOOO much easier (and quicker) than grinding, filing, sanding etc... Mind you, using a press as a "mill" will shorten the life of the spindle/column bearing, but they are cheap and easy to change. Just take light cuts is all.