QB79 Ninja - The $200 PCP

[rsterne]

It's a great solution for the QB79 because it's a bolt on deal.... Any of the available mods that work on CO2 will also work with this setup, returning even higher performance.... You can do the same thing with a QB78, but you have to shorten the tube, drill it for the tank block, and ideally inlet the stock to add the two front stock screws as well for extra strength.... That places it beyond the ability of many, and I'm hoping that with my idea of eliminating most of the valve on the QB79 (in Stage 2) that the performance difference between them on HPA will shrink.... It's already a non-issue on a stock gun, or with my "Stage 1" tune.... only the more powerful tunes show up the difference to any degree anyway....

Bob

[Ribbonstone]

Two-part text:

Sanity reasserts itself.  The 2nd, 3rd, 4th, and 5th tanker I tried HATES contact between the bottle and the barrel.
http://www.gatewaytoairguns.org/GTA/index.php?topic=49855.0

That one gun, one barrel, seems to stand alone in preferring contact.  Don’t know what exactly to make of that, but am going to do what the barrel/test targets tell me it needs.

I feel a bit relieved.  The world is round, gravity works, and MOST guns/barrels resent hard contact with air vessels.

Part 2: QB 78 owners:

Lets say you already have a QB 78 and are reasonably handy with hand tools (no machine tools required), can still join in the fun.

If you can do a little DIY, can convert it to HPA. 

Need a gas block.

The current standard QB gas block has changed a little bit, taking 4 o-rings rather than two.  Not real sure how that helps, as ONE o-ring that works right will do the job.

Follow this tutorial for tube cutting and gas block attachment:
http://www.gatewaytoairguns.org/GTA/index.php?action=post;msg=472273;topic=49871.0


End up with a long tubed QB79.

Here is a short-tubed HPA 79 and a long tubed HPA 78.  These two are my "hook'em" guns. Likely to be tanken out to family gatherings, picknics, etc where i can "hook" newbie shooters.




Now Rsterne can tell you about the advantages for making power of a large amount of air “on deck” (air that is already regulated and just waiting to push your pellet.  If you have visions of high power, can either extensively mod the valve of a QB79 to gain some of that on-deck air or can convert a Qb78 and do less extensive valve mods.

If you consider the cost of a used QB you already have to be about $60.

QB gas block $35 (which would be fine for running at 1100psi or under)
JDS gas block $55 (which I would recommend for +1200psi output)
Ninja 1100psi tank = $80

Plus and afternoon of sweat.

OR if you have to buy new, call it $205…but you’ll have to ship from 3 different places so that would considerably up the cost though shipping.

But if you have a QB78 in hand, can consider that as “already paid” and think in terms of  “$105 to make it HPA”.

Lets look at it in the simplest way:

If you have 45 cc’s of on deck air volume, and you shoot one shot, finding the air pressure has dropped form 1100 to 600psi, then the NET push was 850psi.  If you have 90cc’s volume and after one shot, the pressure dropped to 850psi, then your net push was  977psi. 

[rsterne]

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....



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

[Ribbonstone]

 like the simplicity of the HPA QB's, long or short tubes.  Easy to take apart, change what you want or fix what is not right.  If simplicity is a virtue, then these are honorable guns.

[rsterne]

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....



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....



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

[NinjaPaintballRay]

Bob.  Amazing work.  This forum is very lucky to have someone with your knowledge helping people out.  Thanks for doing what you do.

[airpuffhunter]

Hello Bob, a little bit off, but would it be possible to drill the barrel in the back, so you can make a pass trug a bolt to engage in the spacer behind the valve, replacing the one that comes stock, but holding the barrel in place.
so you don't have to remove the barrel from the receiver every time you want to disassemble the gun?

[rsterne]

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....



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

[rsterne]

I swapped out the tank for the other one that I had set up for 1500 psi.... I wasn't quite sure what to expect, as normally that is too much pressure for stock hammer spring preload on a QB78.... As it turns out, with the smaller plenum of the QB79, the pressure drop during the shot compensates for the extra pressure at the beginning of the shot.... allowing the stock hammer spring to work OK.... Here are the results of the Stage 2 tune running at 1500 psi....



As before, the starting pressure was 2000 psi, and the ending pressure was 1000.... I got 16 shots averaging 918 fps (26.8 FPE) down to 1400 psi before the velocity started to drop below 900 fps.... The fact that the drop in velocity starts 100 psi below the regulator setpoint indicates that this tune is operating very close to the "knee" of the curve where I like to tune my regulated guns.... The efficiency was higher than at 1200 psi, working out to 0.80 FPE/CI, and I should be able to get 42 shots @ 27 FPE on a 3000 psi fill.... That a pretty serious hunting platform....

When I did the calculations for the pressure during the shot for the 12 cc Plenum, I get 836 psi at the end of the shot, and an average pressure of 1168 psi during the shot.... That gives a pretty good indication of why the stock hammer spring preload is working so well with this setup.... It also confirms that running 1200 psi on the Stage 2 tune is running less efficiently than it could because the hammer energy is too much for the 880 psi average pressure.... I now have no doubt that reducing the preload a bit on that tune will increase the shot count with little or no velocity loss.... I'm going to have to give some thought to what is the easiest way to accomplish that, as fitting an RVA to a QB isn't the easiest thing to do, and I want it adjustable, I don't want to just clip the hammer spring....

Bob

[rsterne]

Just out of curiosity I flung a few 18.1 gr. JSB Heavies through the Chrony.... They did 855 fps (29.4 FPE).... That's 3 FPE better than the best I ever did with a QB79 at 1500 psi with those pellets previously.... so the new "Maxi-Valve" certainly works great.... Also, so far, it doesn't seem to leak, despite not having the O-ring "squeezed" between the valve halves.... I would say the "Maxi-Valve" idea is a complete success in the QB79....

Bob

[joel w]

Thanks Bob, I think you have just added to my addiction by giving me my next project.   

Brilliant!

[Froggy.]

Bob, change the cocking action to a pull rather than push...easy to add a hammer spring adjuster like the 2240 crosman.

[rsterne]

I agree, Froggy.... The problem is, that the spring then holds the bolt forward, eliminating virtually all of the loading room for the pellet.... You have to either hold the bolt back during loading, or make another notch at the back to do that, like this....



I may well do that if I can't come up with a better solution.... without resorting to the complicated RVAs others have built for QB's that are still "cock on close"....

Bob

[Ribbonstone]

Not really a solution, but it does make it marginally easier to tune a QB.  I leave everything off I possibly can between spring changes.

No safety, no stock, no barrel band, not scope.  Just the bare metal work, set in bags, shooting over the chronograph bare-barreled.

Is one of the reasons I use an on/off between the tank and the gas block.  PROBABALY safe to remove one of the retaining screws (the front action screw) in order to swap springs, but I’d much rather turn the on/off to “off” and fire off the pressure in the tube firs (but keep the pressure in the bottle while I do it).

Once I get where I wanted to go,  put it all together again and then worry about accuracy.

Which might be my 2nd point: I usually have a definitive goal.  Either “X” amount of energy or “x” amount of shots per fill (or both).  If I was testing the limits, then it would be a never ending process and I’d just have to figure out an acceptable way to adjust mainspring tension externally.  I'm personally glad you push the limits (but it's a greedy though as well, you do it so i don't have to).

Then again, I do shoot a Raider, so the 2nd bolt notch isn’t too odd an idea for me to deal with.

[rsterne]

I drew out a couple of different methods, none of which I liked, so I decided to go to the above system which works really well.... The end block is drilled off-center for a 2" long 10-24 SS screw as in the photo.... The set screw in the side of the block pushes a piece of Delrin rod against the side of the screw to act as a brake so it won't self-adjust.... All I have left to do is mill the second down-slot at the back of the bolt travel, remove the rear cocking pin to convert to "cock on open", and I'll be ready to go.... I use an RVA so much when I'm tuning I feel lost without it.... I absoultely HATE having to swap out springs (and clip them) all the time....

Bob

[supertech77]

just as you said bob, it works great on the 850 hammerli, with the long valve previously installed to go 9oz co2, as i have done all the other mods listed on the 850 site, i filled to 2500psi, and i have not set up a crony on it yet but its banging threw a 1inch phone book where it use to only go in 1/2 way, thanks for your idea,i did have to remove 1 inch of the stock to make it fit with the gauge and fill nipple, but it works great;;;; happy,happy,happy  now the 850 is hpa,

[rsterne]

Well, sometimes you pay for not keeping good notes.... I made an offset RVA as in the photo above, removed the rear cocking pin to convert to "cock on open", and machined a new downwards slot to hold the bolt back while loading the pellet.... The only problem was, that the version I previously did that on had a shortened hammer and guide pin on the cocking block to allow the bolt to be drawn back further without it bottoming out.... When I adjusted the RVA so that I could push the bolt down into the rear slot, the hammer spring didn't have near enough preload on it.... Rather than modify the hammer and guide pin, I made a spacer to slide over the guide pin on the cocking block to increase the hammer spring tension.... The spacer was 0.35" OD, 0.22" ID, and 0.30" long, so it adds that much preload, and allows the gun to function properly.... I then proceeded to test the velocity at various preloads, with the following results....



You can see the typical plateau in velocity you get on a regulated gun when the hammer strike is more than required.... The velocity doesn't increase, the gun just uses more air.... One slightly unusual thing on this graph, is that the efficiency falls off on the right side as well.... For some reason, the power drops off quicker than the air usage when the gun is detuned below 800 fps in this Stage 2 configuration.... My choice with this setup, at 1500 psi, would be to tune the gun for just over 900 fps (26 FPE).... I would expect about 50-60 shots at that power level.... Pushing for more power than that with a QB79, even with the "Maxi-Valve" simply wastes air....

Bob

[rsterne]

Here are the results of a full string starting at 3000 psi using the Stage 2 "Maxi-Valve" setup running at a regulator pressure of 1500 psi.... I set the RVA to 2.5 turns out, which set the velocity just where the "knee" of the curve starts, with the 14.3 gr. Crosman CPHPs....



The average velocity was 908 fps (26.2 FPE) with a high of 914 and a low of 902 for an ES of 12 fps (1.3%) over the first 58 shots.... Shot 62 was just outside a 2% ES and wasn't counted, and the pressure at that point was 1300 psi.... As is typical when you tune a regulated gun to the "knee" of the velocity curve, you can shoot a couple of hundred psi below the setpoint before the velocity takes a dive.... The efficiency worked out to 1.07 FPE/CI, which for this power level in a QB79 is pretty astounding....

I'm extremely pleased with the results of this testing.... I think it would be very difficult to get more power than this from a QB79 without major changes to allow running a burst disc higher than the 1.8K which is required for safety the way the gun is produced.... While more power could be produced from a QB78 because of the larger tube, when you consider the simplicity of just screwing a tank onto a QB79 to convert it to a PCP it's a pretty impressive combination.... I will be re-fitting the 1200 psi standard SHP Pro regulator for final testing shortly....

EDIT: I should mention that using heavier pellets would increase the FPE.... 18 gr. would give about 29 FPE, 25 gr. about 32 FPE, and 32 gr. about 35 FPE....

Bob

[Raizer]

That gun is coming along in leaps and bounds mate!

[rsterne]

Today I refitted the stock Ninja SHP Pro regulated tank to the Stage 2 QB79.... I then shot 10-shot strings to check the velocity and air pressure drop for different hammer spring preloads so that I could calculate the efficiency.... Here are the results....



As I suspected during the initial testing of this version, the stock hammer strike was too much, wasting a significant amount of air.... The original tune suggested about 50 shots on a fill, but if the efficiency could be bumped up to 1.0 FPE/CI I predicted 73 shots.... Now I'm pretty confident that can be met or exceeded, since at 4 turns out I was seeing an efficiency of about 1.15 FPE/CI.... Now when using only 10 shots, and a gauge with 100 psi increments, it's easy to have some errors creep in.... but that 10 shot string only used 220 psi, or 22 psi per shot.... while returning 845 fps (22.7 FPE).... I'm looking forward to running a full string starting from 3000 psi as soon as I have my SCUBA tank topped up....

Bob