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PostPosted: Mon Jul 15, 2013 4:15 pm 
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This thread will be slightly different than most of mine, in that it is about building a very simple yet efficient PCP for about $200.... You won't need any special tools, and there are only two things to purchase:

An Industry Brand QB79 Airgun
A Ninja 13CI/3000 psi tank with an SHP Pro Regulator

What you end up with is a gun that looks like this.... It weighs 6 lb. 10 oz. and balances right on the foregrip....

Image

and shoots like this.... In fact twice that many shots on a full tank....

Image

The average velocity while above the regulator setpoint was 609 fps with Crosman 14.3 gr. CPHP pellets, which works out to 11.8 FPE.... On a 3000 psi fill, it works out to 135 shots and refilling at 1100 psi.... for an efficiency of 0.95 FPE/CI....

What does it take to accomplish this great combination?.... Would you believe mount the tank on the gun, fill it with air and start shooting?.... First a little history.... The QB79 is the "tanker" version of the QB78, which was developed from the Crosman 160, and manufactured in China.... It is available for between $100-$120, and is intended to use a CO2 Paintball tank, although many people substitute Paintball HPA setups instead.... So what did I do that was different?.... Instead of the commonly available 13 CI / 3000 psi tanks that have a regulated output of 800-850 psi, I used Ninja Paintballs new SHP Pro version.... The "SHP" stands for "super high pressure" (advertised at 1100 psi) and the "Pro" refers to their "360* twist technology" which allows the tank to be rotated so that the fill nipple and gauge don't interfere with the barrel.... I recently reviewed the SHP Pro, which lists for $80 US, here.... topic56198.html

OK, so the QB79 is designed for CO2, but we're running 1100 psi, what about safety?.... What people forget is that CO2, while having a nominal pressure of 850 psi at 70*F, can produce pressures as high as 1900 psi at 120*F.... At 90*F, it's about 1200 psi, and at 100*F about 1400.... and we don't hear of QB79's exploding on a hot day.... About all that happens is that when it gets hot, the velocity drops, because the hammer spring peaks out at about 1100-1200 psi.... Having said that, there are a couple of recommendations I have on the QB79, whether on HPA or on CO2....

Don't remove the action from the stock with gas in the gun.... There are two additional stock screws that thread into the tank block and provide an additional safety measure should the other screws yield....

Don't remove the breech with gas in the gun.... The valve is only secured with one screw, but sits against a steel block.... That steel block is secured on the bottom by the stock locating stud and on top by the flathead screw in the breech, located under the barrel.... ALL THREE SCREWS must be in place and tight before the gun is pressurized....

The Ninja SHP Pro regulator is equipped with two burst discs, one to protect the tank from overfilling, and the other to prevent the output pressure from rising about 1800 psi.... This is ideal for our purposes, as those pressures can be reached in a CO2 system, and in fact CO2 tanks are rated at 1800 psi.... As long as you don't disturb the 1.8K downstream burst disc, your QB79 should be just as safe as running on CO2, IMO.... I chose the SHP because of its 1100 psi output (my tanks actually measured at 1200).... Remember I mentioned earlier that the hammer spring in a QB peaks at about that pressure?.... That means that the gun should be shooting pretty efficiently without having to change it.... If you are only running 800-850 psi the hammer strike is actually too strong, and the gun will be wasting air, and may experence hammer bounce.... It still might get lots of shots, but clipping a coil of two off the hammer spring would improve the shot count even further....

Please note, I made NO modifications to the gun in any way.... I did disassemble the breech and deburr it and the bolt and the rear section of the main tube, and I polished up the trigger and hammer and installed a lighter trigger spring and 2-stage plunger.... but those are all fine-tuning details that anyone might do to a CO2 version and have nothing to do with the performance, only functioning and shooting enjoyment.... You have to slide out the barrel to rotate the tank to install it, as the gauge and fill fitting won't clear.... but that gives you the opportunity to deburr the forward section of the breech so it doesn't keep shredding the O-rings anyway....

I think this conbination of the QB79 and the Nnija SHP Pro setup is just about perfect as an introduction to PCPs.... The price is certainly right, and the platform can be modified to your heart's content.... The target style AR2079 version isn't a lot more money, and the conversion process is identical.... IMO, the QB79 and the Ninja SHP Pro go together like bread and butter.... and just in case you might be interested in spicing up that combo a bit, stay tuned as I have a couple of simple mods in order as well....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Mon Jul 15, 2013 4:32 pm 
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Very nice and concise! :D

Now to buy those two tanks!

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PostPosted: Mon Jul 15, 2013 7:34 pm 
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Very interested in this.. was the rifle non pal to start... with the new tank it ends up over 499fps? thx

edit: I'd like to get into pcp mainly for accuracy and lower decibels. Would a non pal version of this rifle with a hipac system work well? Also will it stay under 499fps? cheers

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PostPosted: Mon Jul 15, 2013 8:50 pm 
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The .22 cal is non-PAL, the .177 I'm not sure.... If you wanted to build a non-PAL version on HPA, you can certainly do it, I did it a couple of years ago and posted the information on this Forum but I can't find it now.... Here is a link to another site.... http://airgunhome.com/agforum/viewtopic.php?t=7656

In .22 cal it required the regulator set to about 625 psi to stay under 500 fps.... plus a lightened hammer and some coils cut off the hammer spring to get better efficiency.... Incidently, there is a lot of information at that link about the trigger work I did, which I repeated on this gun....

You will have great difficulty getting under 500 fps with a HiPac because of the high pressures they run....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Mon Jul 15, 2013 9:23 pm 
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Bob this is perfect timeing :D I was looking to get the 79 and doing the same as you have done but sniper Dan doesn't have any in stock so I'm picking up the 78 this week and if I'm not mistaken this can also be done to the 78 ?

Great post as usual Bob thanks for sharing and can't wait to see what else you have up your sleeve for this. :wink:

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PostPosted: Tue Jul 16, 2013 12:16 am 
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Today I removed the barrel and breech to ease the restrictions and increase the airflow.... I did NOT remove the valve from the gun, all mods were made to the barrel and bolt only, plus I installed a larger transfer port seal, from a Crosman Disco/22XX/13XX.... just the rubber seal only, not the metal sleeve.... I got that idea from Tim at Mac1, and it really works great, doing a perfect job of sealing the curved valve to the curved breech, and it's larger than you can go on the porting on a .22 cal barrel....

I drilled out the barrel port one number drill at a time, starting with the #28 (0.140") and ending with the #20 (0.161").... That makes the transfer port 75% of the bore diameter, which is as large as you dare go without creating loading problems for the pellet.... The area for the airflow is a third larger than stock.... I then drilled the nose of the flow-through bolt out one size at a time, starting from the #34 (0.111") and also ending at the #20, so that it was the same size as the barrel port.... That greatly enlarged the hole in the bottom of the bolt where the air flows through, and I used a 1/8" ball grinder tip in a Dremel to smooth and enlarge the slot formed until it was the same area as well.... After careful deburring of the inside of the barrel and bolt using a needle file, I reassembled the top end of the rifle and tested it again.... Here are the results....

Image

The average velocity while on reg. jumped up to 738 fps (17.3 FPE), giving 48 shots starting at 2000 psi before the velocity dropped below 730, and a total of 58 shooting down to 1000 psi.... That works out to 17 psi per shot, and an efficiency of 1.10 FPE/CI.... Starting from 3000 psi, you should get 105 shots down to just under 1200 psi.... This mild mannered gun is beginning to show some real promise.... The Stage 1 mods to accomplish it can all be done with a set of numbered drills and a needle file, plus a rubber seal.... and without removing the valve from the gun....

For the next round, however, I will be pulling the valve out to improve the airflow into the valve, and provide more volume between the regulator and the valve to increase the average pressure available during the shot cycle.... I'm really looking forward to seeing the results....

Ace, you will need the tank block from a QB79 and will have to shorten and modify the tube and stock to use a tank on it.... It can be done, just more work....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Jul 16, 2013 10:04 am 
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I "wood" like to see that with a full stock....... :mrgreen:

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PostPosted: Tue Jul 16, 2013 12:13 pm 
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Based on previous experience, where I got a significant gain on a 32 FPE QB78 running at 1600 psi, I cut off the flow-through bolt probe, squared off the end of the bolt flush with the back of the barrel port, drilled the bolt and installed a 3/32" diameter extended probe that is 0.10" longer than the original flow-through (because it pushes up inside the skirt).... Whereas on the previous time I did this mod I gained 32 fps, this time I lost 5 fps.... However, the ES seems slightly less (ie fewer high velocity shots).... The only explanation I have for this, is that on the more powerful, higher pressure version, where flow is more important, the thin probe is better.... However, on this version, running lower pressure and half the air volume through it, there is very little difference, and it isn't worth having to use a lathe to make the change to the bolt, simply drilling it out works just as well.... When I increase the power further, I would expect the thin, extended probe to work better, but of course I can't go back and test the flow-through now, all future testing will be with the 3/32" diameter probe....

Basically, either drilling out the flow-through nose.... or replacing it with an extended probe.... work equally well at this pressure (1200 psi) and power level (17 FPE)....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Jul 16, 2013 7:30 pm 
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Here is a photo of the valve I will be installing for my "Stage 2" mods.... The 1/4" wide aluminum ring is all that is left of the front part....

Image

It was epoxied onto the rear portion using a #113 O-ring for a spacer (just touching).... When the JB Weld was 4 hours old (not sticky but not hard) I cut the O-ring and peeled it out of the groove and then cleaned up the front of the groove with a razor blade to remove any excess epoxy.... Once hardened, I will turn it around and face off and bore out the inside to increase flow into the poppet seat....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Jul 16, 2013 8:17 pm 
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Great post Bob,your getting me motivated,I already have the tank.
Do you know if they make a QB 79 deluxe ,I 've never seen one ?..kelly


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PostPosted: Tue Jul 16, 2013 9:38 pm 
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Not as far as I know.... The QB79 already has the larger (15mm OD) barrel, however, it just lacks the gold trigger and bolt handle.... ambi stock, though, no cheek piece....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Jul 16, 2013 9:46 pm 
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rsterne wrote:
The .22 cal is non-PAL, the .177 I'm not sure.... If you wanted to build a non-PAL version on HPA, you can certainly do it, I did it a couple of years ago and posted the information on this Forum but I can't find it now.... Here is a link to another site.... http://airgunhome.com/agforum/viewtopic.php?t=7656

In .22 cal it required the regulator set to about 625 psi to stay under 500 fps.... plus a lightened hammer and some coils cut off the hammer spring to get better efficiency.... Incidently, there is a lot of information at that link about the trigger work I did, which I repeated on this gun....

You will have great difficulty getting under 500 fps with a HiPac because of the high pressures they run....

Bob



Thank you for this.. :-D



do you remember the ebay seller for the tank? not finding one that will ship to Canada...

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benji classic .22/ HIPAC 2260 .25/QB78 PCP .22/ 2289 .22 FTP/ 1377 .177/ polished 357crosman .177/ 2240 .177 /P17 .177/ G&G .45 6mm

"When Obi-wan talked about the darkside of the force who knew he was referring to windows...?"


Last edited by doublevision on Tue Jul 16, 2013 10:19 pm, edited 1 time in total.

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PostPosted: Tue Jul 16, 2013 9:48 pm 
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rsterne wrote:
Not as far as I know.... The QB79 already has the larger (15mm OD) barrel, however, it just lacks the gold trigger and bolt handle.... ambi stock, though, no cheek piece....

Bob

Thanks,I'll start looking for one..kelly


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PostPosted: Wed Jul 17, 2013 10:04 pm 
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I did some more work on the Stage 2 "Maxi-Valve" today.... The concept is to turn all the volume between the valve seat and the QB79 tank block into usuable valve volume.... Here are the results....

Image

I machined a 0.10" long spring seat into the end of the poppet to fit the stock QB valve spring and then tapered the sides of the poppet on a 5* angle to reduce the OD to that of the spring at the seat.... The support for the front end of the spring is made from a 1.5" long 8-32 SHCS with the head turned down a bit to fit inside the QB spring.... I made a tapered brass collar to slide over the screw to form the spring seat, and then drilled out a piece of 3/16" brass K&S hobby tubing to fit over the screw as a spacer to set the height.... The tank block will be drilled and tapped on center for the 8-32 screw....

It turns out that in a stock QB valve, the installed spring is compressed to 1/2" long, so as long as I have that distance between the spring seats I will have stock preload.... It works out in my QB79 that I need the front spring seat 1.035" from the tank block to acccomplish that.... Here is a view of the inside of the valve, showing what the flow is like....

Image

If you compare that to a stock QB valve, you will see a huge difference.... The ID of a stock valve is 7/16", my valve is bored out to 1/2", which doubles the clearance around the poppet.... The aluminum ring I glued on is 1/4" long measured from the O-ring groove.... After the epoxy hardened, I machined out the front of the valve on a 30* angle until there was only about a 0.020" lip remaining.... That took the taper about half way to the seat.... I then changed the angle to 15* and knocked off the corner to smooth the flow even more....

The throat of a stock QB valve is 0.198" and the stem is 0.116".... I drilled the throat out to 7/32" (0.219") so that the throat area is larger than the rest of the porting I did in Stage 1.... I also blended the bottom of the exhaust port into the throat using a 5/32" ball grinder in a Dremel.... The distance from the valve seat to the tank block is just over 2", which gives a basic volume of 14.5 cc.... but by the time you subtract the volume of the poppet, spring, and forward spring mount, I ended up with a whisker over 12 cc.... While it's not as much as I'd like, it shouldn't cause too much loss in efficiency until the power goes over 25 FPE.... I'd frankly be very surprised to see that power level, even with my "Maxi-Valve" installed, when running at only 1200 psi....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Jul 18, 2013 1:08 pm 
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I drilled and tapped the tank block for the front spring mount and assembled the Stage 2 version of the gun this morning.... I was quite pleased with the results, as I have exceeded stock Disco performance with this version.... Here are the results from a 2000 psi to 1000 psi (tank pressure) string....

Image

The first 22 shots averaged 864 fps (23.7 FPE), dropping below 860 fps only once the pressure dropped below 1200 psi which is the setpoint on my Ninja SHP Pro regulated tank.... That should give 50 shots on a full tank, which is pretty decent at that power level, even though the efficiency (to me) is a bit disappointing at only 0.74 FPE/CI.... It is quite possible that reducing the hammer spring preload would increase this efficiency somewhat.... The gun may well be operating on the "plateau" of the velocity curve, and reducing the hammer strike a bit may well not drop the velocity while increasing the shot count.... I'm pretty sure that dropping the velocity just a bit (20-30 fps) could add maybe 10-20 shots to the string, so that is something worth experimenting with at a future date.... If we could get the efficiency up to 1.0 FPE/CI at 22 FPE, 73 shots should be possible....

With the relatively small 12 cc plenum, which is only 1/2 cc per FPE at this power, the average pressure available per shot is less than 900 psi.... How is this possible?.... We start out with 12 cc (0.73 CI) of air at 1200 psi (83 bar), which is 60.6 CI of air a 1 bar.... Each shot is using 36 psi from the 13 CI tank, which is 32.3 CI of air at 1 bar.... Assuming the regulator response time is too short to add any useful quantity of air during the 1-2 milliseconds before the valve closes, at that moment we only have 60.6 - 32.3 = 28.3 CI of air at 1 bar left in the valve.... That means the pressure has dropped from 1200 psi to (28.3 / 60.6) x 1200 = 560 psi, so the average pressure during the shot is only 880 psi.... It shows how important plenum volume is in a regulated gun.... If we had double the plenum volume, the average pressure would be 1040 psi, much closer to the 1200 psi setpoint.... and the efficiency would be significantly higher.... On the other hand, this is pretty remarkable performance on a QB79 from only 1200 psi, thanks to the much increased volume of the "Maxi-Valve"....

About the only thing left to do is to test this gun running at 1500 psi, which is an easy level to achieve with the Ninja SHP Pro regulator and still be within the safety levels provided by the 1.8 K burst disc.... How to change the regulator to that output is in the separate thread on the Regulator referenced in the first post in this thread.... As time permits, I will be doing that and reporting the results....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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