Author Topic: QB78 conversion attempt (Read 2315 times))

Mr. Panther · « **on:** March 27, 2018, 04:59:15 PM »

When I bought the gas block for a QB79 I originally intended to do a conversion of a 22xx type carbine regulated bottle. But seeing as I had two QB78's in .22 , (one I ordered by accident thinking I hit the .177 button), I decided to go with that and see if I could do this. So far it went VERY fast as it is a minimal amount of actual metal fitting to do. I opened up the valve, and did a few more odds and ends. Soon I think this will be done .
Had a lot to go on from all the articles on here, so I checked and double checked everything. I'm setting it up for 850-900 psi so after it is tuned in it should run good on either CO2 or air with out much difference in performance. Good thing about this is I can shoot it with a 13 ci. tank or a 9 oz CO2 tank or use my paintball adapter and shoot single cartridges I like it when I can use multiple sources of gas/air. I will let y'all know how it turns out, as it should be done in a few days, (I have to slow down it is going so easily).
* P.S.... Thanks to Ribbonstone, Nervoustrigger, and rstern, for all the input on your articles. It made this an easy conversion with out all the by guess and by gollies.

Ribbonstone · « **Reply #1 on:** March 27, 2018, 05:55:16 PM »

LEts us know how it comes along, aren't any real tricks or pitfalls, but if there is an issue along the way, are several here that have figured out work-arounds.

Mr. Panther · « **Reply #2 on:** March 28, 2018, 01:18:12 PM »

Got it all done today. Only took about 20 mins. to put back together. Used a paintball adapter on it to see if it held "air " and no leaks yet. Going to let it sit overnight and see if it stays " lit ". LOL I used 70 duro urathane in it everywhere, bolt, valve, gas block, barrel, as I found with my Disco they don't seem to be as fragile as the rubber ones and they are good with CO2 or HPA. They should outlast the rubber too, and really aren't that expensive.
Well now to let it sit for a while and check on it tomorrow to see if it is still good. I did take a bout 3 shots with it and with all the valve work, bolt work and porting I did on it, it barks pretty good, so I'm happy. Probably will be a gas hog, but it is alright as far as I am concerned, as shot count isn't something I was looking for.

HYspd · « **Reply #3 on:** March 28, 2018, 05:43:46 PM »

cock on open mod and an RVA screw will take care of the gas hog part.....my .22 gets like 80 shots at 800fps with jsb 18.1 ammo from a regulated 13ci tank....

Ribbonstone · « **Reply #4 on:** March 28, 2018, 06:28:15 PM »

If you are running a lower pressure output (like one of the 850psi versions), haven't needed to do anything drastic to the issue parts.

A lighter striker helps. Really light may not be what you want, as usually really light strikers need stiffer than striker springs/cocking effort. I rather like a lite "pinky cock" rifle.

The cock on opening feature has some drawbacks, but it does make it easier to make an external spring tension adjuster (AKA "power adjuster"), which makes it easier to dial it in for minimal air use

The dual gas use on a converted QB78 seems good, but it has some draw backs. Without some kind of extended drop down tank-block, the HPA bottle isn't going to just turn off the rifle. The gauge and fill nipple won't pass under the barrel. Now once we get one of these guys sealed up and not leaking, really don't want to distrube the gauge block...so you'll have to de-scope, rmeove the barrel band cross screw, remove the barrel breech set screw, pull the barrel straight forward and off, then unscrew the HPA tank and screw on the co2 paintball tank (or 12gr. adaptor). Then reverse the barrel take off directions....then re-sight the rifle.

I did do the above ever major season change (cold to warm) with a 5mm conversion, running an 850psi out put HPA tank in the winter (about 13.5 foot pounds), and small bottle (3.5oz) co2 tanker during the summer (about 11.8 foot pounds).

BUt...as airgun "nuts" we are likely to gather more and more rifles about ourselves, and once I bought a 5mm PCP, I've left the 5mm Qb conversion running on co2.

Mr. Panther · « **Reply #5 on:** March 28, 2018, 07:23:21 PM »

Yeah i have a drop down block for running the HPA. I have one on my other QB79 HPA too. That one has a RVA and open on cock set up. I don't mind the usage on this one, as it isn't really for plinking, just pest duty. If I want to plink I have a HPA 2260 that fills quick with a pump or I have my 2 discos. I figured it will do good dual duty as I am setting it up for CO2 pressures and if it hits hard on CO2 I know it will do about the same or better on air.
Basically this was just a little project to see how hard it was going to be to convert the tube safely. It already had a lot of port and valve work done on it, and I figured the added pleneum would give it a few more FPE over a QB79. I still have another QB78 I might convert to this type of set up and 2 more stock QB79's if i want to convert those to a HPA set up. Lots of options for this stuff LOL. Thanks for your input guys.

oldpro · « **Reply #6 on:** March 28, 2018, 07:35:46 PM »

Quote from: HYspd on March 28, 2018, 05:43:46 PM

cock on open mod and an RVA screw will take care of the gas hog part.....my .22 gets like 80 shots at 800fps with jsb 18.1 ammo from a regulated 13ci tank....

Brings up a question does anyone know if my gauntlet kit will direct fit into a QB? Im willing to give one out to someone to try.

Chako · « **Reply #7 on:** March 28, 2018, 07:46:26 PM »

Quote from: oldpro on March 28, 2018, 07:35:46 PM

Quote from: HYspd on March 28, 2018, 05:43:46 PM
cock on open mod and an RVA screw will take care of the gas hog part.....my .22 gets like 80 shots at 800fps with jsb 18.1 ammo from a regulated 13ci tank....
Brings up a question does anyone know if my gauntlet kit will direct fit into a QB? Im willing to give one out to someone to try.

Are you talking about the cock on open and RVA?

Mr. Panther · « **Reply #8 on:** March 29, 2018, 08:24:22 AM »

Travis, I'm not familiar with your Gauntlet set up. I have a couple of these guns< (QB79's/78's), not set up except for stock I might be interested in doing some thing with. PM me some info please.

Gipper · « **Reply #9 on:** March 29, 2018, 09:10:35 AM »

Quote from: oldpro on March 28, 2018, 07:35:46 PM

Quote from: HYspd on March 28, 2018, 05:43:46 PM
cock on open mod and an RVA screw will take care of the gas hog part.....my .22 gets like 80 shots at 800fps with jsb 18.1 ammo from a regulated 13ci tank....
Brings up a question does anyone know if my gauntlet kit will direct fit into a QB? Im willing to give one out to someone to try.

Travis, I have several QB's both HPA and Co2 and at first glance of your video I would say yes it will but trial is the only way to be sure of course. I would be willing to test it for you and I can also bring the rifle to the Arkansas shoot for you to tinker with. If you do not already have a tester lined up let me know.

Brian

nervoustrigger · « **Reply #10 on:** March 29, 2018, 10:57:06 AM »

Panther, I'm glad to hear it's coming along smoothly. Haven't been seeing many QB conversions since the release of the Gauntlet. That's understandable from a cost and effort standpoint but the QB is still a rewarding platform, particularly if you are interested in something lighter for field carry or offhand.

Let us know how it turns out once you've had a chance to test it out. Accuracy has been fantastic in my experience. If it isn't, clean up the leade and crown and make sure there isn't a burr at the barrel port and you will be handsomely rewarded.

Gipper · « **Reply #11 on:** March 29, 2018, 11:33:17 AM »

Quote from: nervoustrigger on March 29, 2018, 10:57:06 AM

Panther, I'm glad to hear it's coming along smoothly. Haven't been seeing many QB conversions since the release of the Gauntlet. That's understandable from a cost and effort standpoint but the QB is still a rewarding platform, particularly if you are interested in something lighter for field carry or offhand.

Let us know how it turns out once you've had a chance to test it out. Accuracy has been fantastic in my experience. If it isn't, clean up the leade and crown and make sure there isn't a burr at the barrel port and you will be handsomely rewarded.

+1

All my QB rifles have been accurate and all but 1 with no additional effort beyond cleaning on my part.

nervoustrigger · « **Reply #12 on:** March 29, 2018, 12:52:25 PM »

Sorry, I forgot to comment on the polyurethane O-rings. It's great for dynamic seals like the bolt because of its superior abrasion properties but for the static seals like the valve and tank block, plain old Buna-N will last longer. Granted polyurethane is slightly less likely to get torn on installation so that's sometimes cited as a reason to use it but in my experience it didn't work out that way. That is, if there's a burr or sharp edge, it didn't matter what kind of O-ring I tried. Every one would get cut until I dealt with the root cause. The problem is also aggravated if the O-ring is too tight (wrong thickness/groove too shallow or durometer too high).

I certainly wouldn't go tearing it apart to replace them...just mentioning it for future reference.

Mr. Panther · « **Reply #13 on:** March 29, 2018, 02:04:18 PM »

Thanks for the info Jason. All I have to do is once I have it all figured out the way I want is to pin the block to the tube. It is one of the 78's I had when you were coaching me through the QB79 build that you set my regulator for. I did this because I wanted some more tube length in this one and was going to running lower pressure HPA along the same pressure as CO2. I had already modded the valve to almost a open face design so it flows real well with the Crosman port gasket thingie. I did all the barrel work soon after I bought it. I use an RVA, but I am not interested in shot count. it shoots nice and hard now and even has a bit of push when it shoots LOL. Putting up a few pics of it . Nothing special but every one likes pics. Now it is compatible for any of those three types of "air" sources, and is what I wanted.

Ribbonstone · « **Reply #14 on:** March 29, 2018, 06:43:32 PM »

Once had 5 running...then 4...now 2. I'm firm in keeping these two (a .177 on top and a .22 on bottom) running as HPA tankers for the life of the guns (or the life of the shooter...whichever comes first)>

VERY likely we have different goals for the rifles. My goal was 200 shots on one normal 3000-850psi fill.

That turend out to be (with a lot of fiddling around) 11.8foot pounds for the .177 ARt2078 (top rifle) and 13 foot pounds for the .22 QB79 (bottom rifle).

Eventually I got them there.

Efficiency isn't freakishly high (more like 1.3-1.35 fpe/cuin)...so for someone with a diffeent goal in energy/shot count could do better.

But before you start thining it's NOT s gas hog, I'll set a lower limit: total of 2000foot pounds per fill up. So...somthing like 40 foot pounds for 50 shots, 30 foot pounds for 66 shots, 20 foot pounds for 100shots, 15 foot pounds for 133 shots, 12 foot pounds for 167 shots, etc. So long as it works out to 2000fpe per 13cuin HPA tank, doesn't really make a difference to air use/efficiency.

But if you have a specific enery goal in mind, then air use isn't really something you'd care about. Even with an 850 reg, can get a .22 up to a respectialbe emergy level for at least enough shots to make you "feel like a boss".

Mr. Panther · « **Reply #15 on:** March 29, 2018, 07:47:36 PM »

Mighty fine looking rifles. Yeah shot count isn't a big deal on my end. CO2 is cheap, air is basically free, so I will use as much as I can to get as much power out of this rifle. I saved as much tube as was possible when I cut it, to get as much air in the tube as I could. I might just take it to 1100 LBS and be done with it, dunno yet. Right now it is what I want, but you know how that goes...things change LOL. Might get a thumb hole synth stock from the arrow guy in NY. they are only $39, he's done right by me when I ordered before. this rifle would fit right in it no problemo. Thanks for the share on the pics and info Ribbon.

HYspd · « **Reply #16 on:** March 30, 2018, 01:32:29 PM »

Quote from: oldpro on March 28, 2018, 07:35:46 PM

Quote from: HYspd on March 28, 2018, 05:43:46 PM
cock on open mod and an RVA screw will take care of the gas hog part.....my .22 gets like 80 shots at 800fps with jsb 18.1 ammo from a regulated 13ci tank....
Brings up a question does anyone know if my gauntlet kit will direct fit into a QB? Im willing to give one out to someone to try.

I'm game to do a mock up for you on my QB78....I need to degas it and change the T-port seal over to the thick wall poly tubing i found the other day before it blows the thin wall tubing out again....opening it up from there is just 2 minutes for 2 screws and a pin....

HYspd · « **Reply #17 on:** March 30, 2018, 01:51:35 PM »

the Crosman gasket doesn't work on this Nervous Trigger built bottle rocket...one shot and it's all about gasket?, what gasket?...i found some 3/16x5/16 poly tubing a few days ago....figure i'll dip it in boiling water to soften it and jam it over the shank of a 7/32 drill bit and freeze it as an up sizing technique because the T-port in the beast t is bigger than 3/16.....I'm thinking of going to Mountain Air for a 25 or 30cal barrel, as it is capable of driving more than the 18.1gr pellet at 800 fps power level that the factory barrel is comfortable with...although the 80plus shot count per fill is alot of fun

Ribbonstone · « **Reply #18 on:** March 30, 2018, 03:14:49 PM »

Haven't blown icemaker tubing yet...a little trouble to get them just the right length for a firm fit. Not that you's be putting real high pressure though them as HPA rifles, but as it works fine in one 3K PCP converted QB, figure being a little over-strong for other rifles wouldn't hurt. (but it does make me wonder why it's used on icemakers...what kind of water pressure were they expecting?)

nervoustrigger · « **Reply #19 on:** March 30, 2018, 03:20:17 PM »

For the most part, the poly tubing is constrained by the walls of the air tube so it really doesn't carry the brunt of the pressure pulse.

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QB78 conversion attempt

Author Topic: QB78 conversion attempt (Read 2315 times))