Author Topic: QB78/22xx frankengun repeater PCP testing, added Peek Valve Poppet (Read 6257 times))

mackeral5 · « **on:** May 05, 2018, 05:02:19 PM »

While waiting for a 350cc carbon fiber bottle to arrive I've been testing this one as a PCP. It has roughly 80cc of air capacity. With a full length oem barrel (21.5") and a TKO, with stock in shooting position, it is right at 40 inches long. The stock will collapse a little shorter. With a loaded mag and a bugbuster scope it tips the scales at 6lb 1oz. This string was shot after simply changing barrels and airing up to 3kpsi. Shooting barracuda match 21.14 gr. Previously the gun was shooting JSB 18.1's right at 910 tethered and regulated at 2100psi with a 14" barrel. I may try a string starting at 2800 which should result in a 900-950-900fps 16 shot string.

nervoustrigger · « **Reply #1 on:** May 05, 2018, 07:01:07 PM »

Mike, that's a nice and clean execution of the project. Good numbers there as well.

I'm curious, are the Baracudas your most accurate pellet or was it just a heavy-ish selection to see what kind of energy it will produce with the full length barrel?

mackeral5 · « **Reply #2 on:** May 05, 2018, 07:46:50 PM »

Thanks Jason. You are correct on the pellet choice, I was simply trying to see how much energy the gun can produce. I don't have the place to do much more than chrony testing in the garage, so I don't yet know about accuracy. Hopefully the bottle will arrive sooner than later--I plan to pack up the guns and go test once the bottle is installed. The bottle will be mounted with the reg facing towards the butt, plumbed in through a p rod gauge port. That way if I don't like the bottle I can just plug the hole with a guage.
.

Mudbugmitch · « **Reply #3 on:** May 06, 2018, 08:36:06 PM »

Very nice numbers. Do you have a write up on the build ?

mackeral5 · « **Reply #4 on:** May 09, 2018, 09:58:02 PM »

I haven't done a good job in documenting the build..... but this evening I did a little more testing while waiting on the bottle to arrive. I swapped back to the 14" barrel and added 3kpsi of air.

I forgot to mention that I ended up going with a stock qb hammer spring vs. the lighter spring I typically use.

With a shroud I added the OAL is 36" and weight is just over 6lb's with a bugbuster and full mag. the paintjob didn't go so well on the shroud, something to deal with later.

It definitely shows how much more air is used when trying to push fpe in a short barrel.

Mudbugmitch · « **Reply #5 on:** May 10, 2018, 02:33:43 PM »

So, is that a QB breech and barrel on a 2260 tube ?

mackeral5 · « **Reply #6 on:** May 10, 2018, 02:47:01 PM »

It's what's left of a disco tube after it has been machined to QB specs. Tube ends up at 19" oal, not much capacity..... Mountain Air sells the tubes. It has a QB repeater upper and I adapted a crosman trigger assembly. An SSG is hidden in the stock/buffer tube assembly. Preload adjustment knob is accessible by removing the stock from the buffer tube.

Mudbugmitch · « **Reply #7 on:** May 10, 2018, 03:35:16 PM »

Sweeeet ! Thanks.

mackeral5 · « **Reply #8 on:** May 19, 2018, 12:28:55 AM »

A little update on this project.....

Still waiting for the 350cc carbon bottle, it should arrive any day now. Went ahead and tore it down to add the prod gauge port and temporarily added a 13ci aluminum bottle with the reg set at 2200psi. While in there I couldn't resist one more trick borrowed from Rsterne's projects----a 2mm valve stem. After a good bit of testing with the short barrel it was time to see what an oem barrel would do.

In scanning old chrony strings, the fastest this gun ever pushed a 21.12 gr barracuda match was 951 fps, which occurred around 2350 PSI. Simply converting to the 2mm valve stem the same pellet now maxed out at 991fps, reg'd at 2200psi. Just over 45fpe. Just for kicks I ran some Eunjin 28.5's across the chronograph. They maxed out at 903 fps. I've never pushed them that fast before. Over 51FPE!! Accuracy is unknown, but at least I know the porting is capable.

Until the carbon bottle arrives and I finalize reg settings, etc I won't be certain what the final configuration of this one will be. It easily shoots 18gr up to the 940's with the short barrel and pushes 21gr around 990 maxed out with a 21.5" barrel. Converting one of my qb repeaters to .25 has been something I've wanted to do for quite some time, this may be the perfect candidate. Only time will tell....

HASHTAG · « **Reply #9 on:** May 19, 2018, 01:08:09 AM »

I have fun shooting my qb78d. This thing looks like a beast. Veryyy nice.

mackeral5 · « **Reply #10 on:** May 20, 2018, 06:03:38 PM »

Finally tracking information shows the carbon bottle should arrive tomorrow. I decided to run a string of the 28.5 Eunjin's and see what she would do, with the 21.5" oem barrel. With a 13ci bottle charged to 3000psi, Reg is set at 2200. This string ended at 2000psi. 25 shots averaging 882fps, just under 50FPE. Cocking effort is still very reasonable, with an SSG and an OEM qb spring. The 2mm valve stem really helps the valve flow without requiring excessive hammer spring.

Nvreloader · « **Reply #11 on:** May 21, 2018, 02:39:08 PM »

Mike

Outstanding results with the heavies,
How much tweaking have you done, to get these results?

Tia,
Don

mackeral5 · « **Reply #12 on:** May 21, 2018, 02:53:03 PM »

Thanks Don.... unfortunately there is very little issue qb78 left in this gun. Let's see... the valve retainer, breech screw, breech plug, and bottom valve screw are all of the unmolested issue qb78 parts. The rest is a mixture of modified qb78, crosman, aftermarket, and homemade parts.

Ssg, delrin poppet, porting, an oversized plenum, reg'd bottle, and a lighter hammer combined with a high pressure tube are the key components.

It will be interesting to see where this one ends up, hopefully I can keep it out of the scrap bin....

Nvreloader · « **Reply #13 on:** May 21, 2018, 03:12:09 PM »

Thanks Mike

I am really thinking about making a new psi tube for the 79, if I can find the correct size,
as it appears that the available valve/reg pelume volume is lacking in the OEM 79.

I think, I have found a way to remove all the garbage from the valve to the reg,
a test will be coming, to see the results.

Playing with this QB is getting to be habit forming. LoL

Tia,
Don

mackeral5 · « **Reply #14 on:** May 24, 2018, 09:16:24 PM »

The 350cc bottle arrived a couple of days ago. It came with a regulator, which I was not very impressed with. The spool and bellvilles may have worked, but they just seemed rather crude. The bonnet seemed downright dangerous---it's threads were very loose fitting to the regulator body and it was made out of what was in my opinion very light, thin aluminum. Fortunately these parts were perfectly replaced by components from a Ninja regulator. After swapping internals/bonnet and adjusting the regulator to 2200psi I found that I have a very slow leak, like a few hundred PSI overnight. That goes on my list of to-do's.... hopefully the leak is simply the ball valve not liking 2200psi..

Today a tin of 34 gr JSB Jumbo Beasts arrived courtesy of the USPS and I tested a few across the chronograph. They maxed out at 14 turns of preload at 872fps, 57fpe. I backed it down to 12 turns and 860fps, 12 turns of preload was A LOT quieter....

Hopefully sometime in the not so distant future I will be able to get out and actually shoot a target at a distance greater than 5' away (the distance from the muzzle to my pellet trap when chrony testing.) I am anxious to see how the barrel likes heavier pellets. I don't have very high expectations of the JSB Beast 34's and the Eunjin 28.5's. I am hopeful but based on everything I've read I don't think odds are in my favor. Maybe the oem qb78 barrel will at least like the 21gr Barracuda's. Previously this barrel shot the JSB 18.1's in the high 800's very well, but the goal this go round is to shoot heavy pellets. Ultimately it may take another barrel, only time will tell.

Gertrude · « **Reply #15 on:** May 24, 2018, 09:50:45 PM »

Fwiw,
My bottled QB 78d loves the JSB 18 and 21 gr.
My barrel has had basic attention to the leade and crown, and my reg is set at 1750ish.
I don't remember what it chronys at, but I will be shooting this weekend, so I can check it for you to have a reasonable comparison if you like.
My QB is amazingly accurate and consistent, and will easily do headshots on GS and rabbits at 100+ yds.
Keep up the great work. I'm looking very forward.to seeing your results 👍

mackeral5 · « **Reply #16 on:** May 24, 2018, 10:43:24 PM »

Gertrude, Thank you for the feedback and sharing of information. I would be interested what your gun does with the 21gr with a reg set point of 1750ish. I would guess it should get into the high 800-low 900 range? Regardless it sounds like you have your qb set up very well. Great work on your part there!

Gertrude · « **Reply #17 on:** May 24, 2018, 11:35:28 PM »

Quote from: mackeral5 on May 24, 2018, 10:43:24 PM

Gertrude, Thank you for the feedback and sharing of information. I would be interested what your gun does with the 21gr with a reg set point of 1750ish. I would guess it should get into the high 800-low 900 range? Regardless it sounds like you have your qb set up very well. Great work on your part there!

Thanks,
But truth be told, on my QB, all credit goes to Jason Nervoustrigger.
He makes QB's shoot comparable to guns costing 10x as much.
In our weekly group shoots, it will stand head to head with several Daystates, FX, RTI, etc.
I named my QB "the 50yd Aspirin Assassin" lol.

mackeral5 · « **Reply #18 on:** May 25, 2018, 11:33:28 PM »

Tonight I ran a string of the JSB Beast 34's. Starting at a 3500psi fill of the 350cc carbon bottle. There were 2 855fps shots that didn't read, for some reason this particular tune likes 855fps, add to that my chrono for some reason doesn't like to transmit duplicates across bluetooth and you will end up missing shots every once in a while. It fell off reg at shot 35 (actually shot 37) then I took a few more shots until it fell off to 840fps. at shot 42 (actually 44) we ended up in the 1800-2000psi range.

Since I am currently mired in this pursuit of fpe and shot count, I can't help but wonder.... If I could get Travis to put a longer stem in their PRod valve, what difference would I see? Or maybe a Cothran valve? I had all but ruled out the Cothran valve until I read Bob Sterne's Disco Double testing with a regulated Cothran valve, the results were impressive. I believe there is a little more to be had in my current valve, but the gun is still very easy to cock and I don't want that to change too much.

When making HST adjustments I realized I hadn't shared a pic of the adjuster. Here's a pic of the HST/SSG adjuster, which is accessed by removing the stock. Basically a brass tube connects to the threaded rod/spring guide of the SSG, the tube runs the length of the buffer tube/stock tube, and a knob is attached to it.

And the JSB Beast string:

mackeral5 · « **Reply #19 on:** May 26, 2018, 04:57:18 PM »

She gained a little weight... Set up with the bottle and a different scope she is now just over 8lb. The bottle is plumbed with 5kpsi fittings into a Prod gauge port. Currently an ASA valve is being used, plans are to drill/tap a regulator bonnet to 1/8 npt and replace the ASA with a 90 degree elbow. After a lot of scrounging through my parts bins I found parts to make a tank mounting system.. An old low scope ring attaches to a piece of picatinny rail. The bottle is firmly secured to the picatinny rail with HD velcro straps. At first I thought of this as a temporary solution, but it turned out a lot better than I thought. I cannot rotate/shift the bottle at all. The original fill port was replaced by a pressure gauge for the plenum.

Not the prettiest gun anymore, I really liked the looks of it in the previous pics. I can't wait to try it out at range.

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QB78/22xx frankengun repeater PCP testing, added Peek Valve Poppet

Author Topic: QB78/22xx frankengun repeater PCP testing, added Peek Valve Poppet (Read 6257 times))

HASHTAG