About to take the plunge .... QB-79 on HPA question ?

[Motorhead]

As a rabid tinkerholic, going get a QB-79 and do all the Charlie da Tuna mods and what ever else I can figure out to "Hot Rod" the QB.
Going to replace Co2 with a small HPA tank which leads me to my question ??

The small HPA "Regulated" tanks can be had in @ 1000#, 1250#, 1500#, 1750# & 2000# regulated.
Being the QB is a Co2 based gun with pressures etc ... If one was to go the HPA route WHAT PRESSURE would be best for a field/sport shooting application in .22 cal ?

Thanks,
Scott

[jonnnyboy]

Scott, I have used the stock Ninja 13ci hpa tank which comes regulated at approximately 850psi.  I have also used the JDS tank regulated for 1000psi.  There was just a little more zip to higher tank pressure and I did not feel I was putting my gun to any undue stress with the 1000psi.

I have read alot of posts that were either negative or positive about using more than 1000psi, but in my case I just decided to stay within what would be normal operating limits of co2 which is 850-1000psi.  I'm sure some of the others will chime in with more experience and knowledge.  Let us know what you decide.

joe

[Motorhead]

Joe,
Thanks for the insight ...
Actually prowling around the web trying to get SPECIFIC conversion info going HPA in the QB's is really salt and pepper sprinklings within tons of threads that would need to be read finding it 

Coming from a strong Paintball background where we fiddled too death with Valves, Spring pressure, Hammer weights with Co2 or HPA pressures changes finding so many ways to find a sweet spot. I am assuming a Co2/HPA/PCP format has the same variables in the broad tuning possibilities 

Not really keen on chasing the FPE figures as more interested in flatter trejectory coming with speed of lighter .22 pellets.  Ideally in my mind would be sending the lighter / mid weight .22 pellets down range in the 800 fps range.

So ... saying that, any others offering insight may better know what route my future QB mods may be best suited.

 

[jonnnyboy]

Scott, I am definitely not an expert or anything but I think you will find that 800fps is on the upper end of what can be easily modded for this rifle.  That's not to say it is impossible, it will take a lot of tinkering.  700-750 seems to be the magic spot and this is the speed which I was trying to reach with 14.3gr pellets.

The basic mods that I felt comfortable doing were the internal deburring and the transfer port/icemaker tubing mod.  I also shimmed with a couple thin washers the hammer spring and smoothed up the trigger.  Mine has a valve that has been drilled for better air throughput and I added a probed bolt to push the pellet just slightly farther past the transfer port.  I also wrapped my barrel with teflon tape over the orings when I reinstalled it to help with any blowby leakage.

These are the main mods I added to my 79 and it is a shooting machine.  I had great luck with my barrel and as you can see, she will do a squirrel easily to 30 yards which is my self-imposed distance.  I have no hesitation taking a squirrel at these distances with this rifle.  Any farther and I am just too shaky shooting off-hand!

Hope that helps.
joe

PS. There are some guys on here who have forgotten more than I will ever know about co2 and especially these guns.  If you get a chance, check in on Ribbonstone and RSterne.  Also, Mike Melick, Tim of Mac1 and @SSS$$$ are all wonderful resources on these guns.  Ask your questions, somebody will know some answers!

[Ribbonstone]

Run 5 guns on 13ci HPA tanks....4 QB's and an AirForce TalonSS.

By preference, use the 850PSI output tanks on the QB's.  Have used higher pressures, but have decided to stick with the low pressure tanks.   IF pushed for a max pressure, would be conservative and go with 1000psi...which is still inside the normal range of pressures a QB tube would be exposed to on a warm day.

Other people certainly do use higher outputs without too many reports of "oops" (although at least one report of the tank block tearing off the end of the tube).

All I know for sure is that these 4 QBs have been running on 850 output HPA tanks for several years with no problems.

[grumpy]

Are you guys beefing anything up internally if converting to HPA ? Was thinking about getting one of the 13ci tanks. Thanks

David

[rsterne]

The QB 79 tank block mounting system has a definite pressure limit.... The screws that attach it are made of soft steel (easily replaceable).... but they are VERY close to the end of the tube.... too close.... I know of at least one HPA converted QB 79 that suffered a regulator failure (no downstream burst disc) and the 2600 psi in the tank went into the gun.... It sheared off the screws, blew the tank block off the end of the gun, and sent the block/regulator/tank assembly spinning across the floor of the shop.... Fortunately, nobody was hurt, although some underwear likely suffered an indignity or two....  

When you consider that CO2 on a hot day can reach 1900 psi pressure at 120*F.... and that I have heard reports of the holes in the end of the tube bulging (which also happened above).... it seems to me that the safety margin on the QB 79 is nearly non-existent, even with CO2.... If you are going to convert one to HPA, make SURE that the regulator has a 1.8K burst disc installed on the downstream side.... That effectively limits the regulator setpoint to a maximum of 1500-1600 psi.... and even those pressures may occassionally blow a burst disc.... Note that even if your regulator is set at 850 psi you MUST use a 1.8K burst disc or you risk a catastrophe in the event of a regulator failure....

The good news is that even at 1500 psi you can get LOTS of power out of a QB 79.... and even more out of a QB 78.... Check out this thread for a comparison....

http://www.gatewaytoairguns.org/GTA/index.php/topic,21681.0.html

I got over 26 FPE from my QB 79 and I'm now up to over 32 FPE from my QB 78.... on just 1500 psi....  

Bob

[Jaymo]

rsterne, did you use the stock QB78 tube when running 1500psi?
Did you do any mods to the valve to improve valve retention?
I've pumped my 78 to 1100 with my Axsor. Never tried 1500.
Has anyone tried installing a longer tube on a 79, to get more volume between the tank and valve?
I was thinking about doing that, so I can tether it to my 48/3000.

Can I rebuild the regulator on my Pure Energy 48/3000 tank to put out 3000 psi, so I can use it with my Marauder, B50, and 909 PCPs, instead of with CO2 guns? I realize the 1800 burst disk would have to be replaced with a 5000 just like is on the tank side.

[rsterne]

CO2 can generate up to 1900 psi at 120*F.... so I wouldn't worry too much about the tube on the 78 & 79.... The 78 has a backup steel sleeve mounted right behind the valve.... so there are a total of three screws (two on the sleeve, one on the valve) locating it.... If you really want to be sure, check to see that the sleeve is right against the back of the valve.... Other than that, I don't see a problem with the 78 safety wise.... HOWEVER, I would make SURE that the gun is protected with a 1.8K (1800 psi) burst disc in case the regulator bypasses.... This is even more important on a QB 79 because of the way the tank blocks is mounted.... They can, and have failed....

If you read through that thread, you will see the results I obtained with my QB 78 after I shortened the tube about 3".... That made it the eqivalent of a QB 79 with a 3" longer tube.... It was very important to get that extra volume.... but the difference between the shortened 3" tube and the full length 6" one was neglible....

I am not familiar with the Pure Energy regulators, I have only worked on Ninja ones.... If you want to bypass the regulator completely, you should be able to just remove the piston, spring and check valve.... 3000 psi in, 3000 psi out.... It might leak, however, and you might have to use the piston (to get the O-rings sealing up) and remove the seat from the piston?.... Not sure....

Bob

[Ribbonstone]

That steel ring inside the gun (the front breech screw and the big thick stock stud screw into it) is right up against the valve.  Have to bend or shear those two thick screws before the valve is going to set back, so extra retention screws aren't needed on that end,

Main plus of using a cut off QB78 tube is to allow a full length stock.

Got 4 HPA conversions (3 on converted 78 tubes), two co2's, and one PCP QB.

[rsterne]

Main plus of using a cut off QB78 tube is to allow a full length stock.

and to get more power.... The extra volume between the regulator and the valve keeps the AVERAGE pressure up during the shot up.... It won't matter if you're not using a valve with the front end opened way up.... but if you are, a 3" minimum length between the valve and tank block really make a difference....

Bob

[Ribbonstone]

Only one that was tuned for max power is the long barreled .25, and I do think the long tube was a help. 

In the mirco moments of the valve opening and closing, am pretty sure the regulator can't add air; the shot happens with whatever volume of pre-regulated air that is between the regulator and the valve.  All the pictured  HPA guns have an on/off. When "off" the rifle's air tube is still charged to the output pressure.

Velocity with the regulator "on" is the same as the one shot taken with the regulator on "off".  IF the regulator does kick in during that small time fame of a shot, whatever air it may be adding to the tube during a shot arrives too late to add to the pellet's speed.

Probably a QB79 sized tube has all the air volume a .177 could ever tap off for a shot...and probably enough volume to make for a pretty fast .22.   But when I wanted to get a .25 up to 30-40 foot pounds on low pressure (currently using an 850psi bottle), needed the long tube to do it.

[rsterne]

In the mirco moments of the valve opening and closing, am pretty sure the regulator can't add air; the shot happens with whatever volume of pre-regulated air that is between the regulator and the valve.  All the pictured  HPA guns have an on/off. When "off" the rifle's air tube is still charged to the output pressure.

Velocity with the regulator "on" is the same as the one shot taken with the regulator on "off".  IF the regulator does kick in during that small time fame of a shot, whatever air it may be adding to the tube during a shot arrives too late to add to the pellet's speed.

I agree 100% and the experiment I did in the thread below was designed to prove just that.... Your findings come to the same conclusion regarding the inability of the regulator to contribute during a shot....

http://www.gatewaytoairguns.org/GTA/index.php/topic,21681.0.html

When parts that would produce over 31 FPE installed in a QB 78 were installed in a QB 79 tube, the power dropped to 26 FPE.... a loss of 15%.... Not only that, but the shot count did not increase, the gun was less efficient, producing less power from the same amount of air.... When I cut the QB 78 tube in half and swapped the parts back into it, virtually all the lost power returned.... I have a rule of thumb that you need 1 cc of volume between the regulator and the valve seat for each FPE of energy you want to keep the AVERAGE presssure during the shot from dropping too much and robbing power....

Bob

[Ribbonstone]

Makes sense to me...pretty good estimate of the volume needed.  Seem to run into a limit tuning the QB on 850psi output.  Past a certain point, won't shoot faster...guessing that there is just no more "on deck" air to move ("on deck" being the already regulated air stored between the  tank and the valve).  Increasing that on-deck air (by using a longer tube) raises that limit.

Past that leveling off point, are going to need more pressure....but there seems to be a wise limit to how much pressure the QB tube  and tank block should be asked to contain.

So the main question is  want output pressure.

Mr. Archer and myself tend towards the 800-900psi area and are probably conservative. Have used 1200 without any problems.  Others seem to like 1400-1500psi.

PERSONALLY...think 1200psi  is safe, but as I have other guns to shoot when I want high energy, will continue to run mine at 850psi.

[grumpy]

Does anyone have a link to the tank and regulator, thats a  good deal ?

David

[rsterne]

When you consider that CO2 pressures can reach 1900 psi at 120*F.... an HPA conversion up to those pressures should be OK as long as you run a 1.8K burst disc and the action is bolted into the stock.... I've run the math on all the QB parts, assuming mild steel components at 1800 psi and here are the safety margins I calculated....

Tube (assuming DOM seamless tubing):  3.9:1
QB 78 end cap threads: >20:1
Wall thickness under threads: 1.7:1 (if seal is inside of the threaded area, does not apply)
Three valve locating screws (including steel sleeve), total shear strength: 2.5:1
Tubing wall yielding (distorting) around the above screws: 2.7:1
QB 79 tank block 4mm attachment screws: 1.2:1 (ie should shear at ~2200 psi in theory, known to have occurred at 2600)
Yield (ie distortion) of tank block attachment holes in tube: 1.0:1 (ie should distort at 1800 psi, confirmed by CO2 gun in hot car)
Tear out of tank block attachment holes in tube: 1.2:1 (ie should tear out about the same time the screws shear off - severely bulged at 2600)

From the above, the weakest design point is obviously the attachment method of the QB 79 tank block.... The holes are way too close to the end of the tube, if they weren't you could really increase the strength by using high-tensile screws (not a bad idea anyway, the stock ones are very soft material).... I did ignore the two screws attaching the block to the wood stock, and the friction of the barrel band.... so there is obviously some additional safety margin IF the action is in the stock.... However, there is no way I would even consider operating a QB 79 on HPA without insuring that there is a 1.8K burst disc on the downstream side of the regulator.... Even then, there is little safety margin left.... although it is the same as for CO2 on a hot day.... For safety, I wouldn't pressurize a QB 79 unless the action was installed in the stock including the extra two screws into the tank block.... I use an additional 3/16" shear pin in between the O-ring grooves (only use the inner O-ring to seal) on my HPA conversions.... JDS Airman now sells a tank block with two additional screws in the same location (you still use the original screws as well).... There is no more problem with tear-out as they are much further from the end.... The two additional 8-32 screws in that location would increase the safety margin to 2.7:1 in shear and 2.0:1 on the tube wall yielding (a 3/16" shear pin even more).... I would use that modification even on a QB 79 operating on CO2, personally....

On a QB 78, the weakest point from a design point of view is the tubing wall in the threaded portion, because the O-ring seals in the middle of the threaded portion, not inside it where the tubing is full wall thickness.... Any bulk fill fitting (CO2 or HPA) would be more than twice as strong in that area if the O-ring is simply moved in further so that it is located inside of the threaded portion, where the tube is full thickness....

Any steel item subjected to repeated stress and relaxation (like filling and emptying an airgun) will be subject to fatigue if it is stressed to more than 45% of it's tensile strength.... What that means is that if you have a safety margin of over 2.2:1 you don't have any concerns with fatigue.... I use that as a minimum design point for any of my HPA projects.... From my calculations, if you have the O-ring on a bulk fill fitting on a QB 78 on the full tubing wall instead of the threaded portion, the gun fulfills that.... Likewise, if you beef up the tank block mounting on a QB 79 with at least two additional 8-32 (or larger) screws between the O-ring grooves, it should also be OK.... provided you drill the holes in the tube accurately so that all 4 screws share the load properly....

I'm not an engineer, so I'm not guaranteeing any of the above.... Just some things to think about on the QBs, whether on CO2 or HPA.... First rule of HPA on a QB 78/9.... MAKE SURE YOU HAVE A 1.8K BURST DISC....

Bob

[Ribbonstone]

Think we're confusing the poster a bit.
 But considering that air pressure increases less drastically than co2 with temperature increase, a good argument can be made that an 850psi HPA tank is LESS likely to cause a problem than a co2 tank.  IF both exposed to 98F (which is not a terribly unusual temperature), which would stress the tank block mounting system more?

So I'll take the stand that over all (considering all the temperature ranges a gun is normally used in), 850PSI output  air is less stressful to the mounting system than co2.

UNLESS the regulator fails...and they can. Inside there is a spring controled piston kind of per set to only let out a set pressure of gas.  That piston has a seal that blocks the vent from the 3K tank at some set pressure.  But that seal can leak, letting the air pressure creep up.  If it totally fails, then all 3K of air is dumped thought the regulator.

There is a burst disk (a safety feature, kind of like a blow off valve on a hot water heater) on the reg.  Would be good to have that burst disk be a 1.8K one rather than the 3K ones that are often used.

I may be paranoid, but will also use a RAP4 on off.  Does have a gauge to read the output pressure (which can help diagnosis creeping pressure from an almost-sealing regulator) but it also has a burst disk.  That way, can put two 1.8K burst disks between the 3K tank and the gun.

[Motorhead]

This post makes a LOT OF SENSE, as do the others BTW .....
So it absolutely is a MUST HAVE item the 1800# burst disk on the downstream regulated air space.

What question not getting directly addressed is that of What is an optimum pressure regulation for Hot rodding a Qb79 on HPA in .22 cal ?  ( 850# being generic and safe .... 1200# pretty normal for Co2 at 90*F )

Not wanting to sound anal, but .... ?

Think we're confusing the poster a bit.
 But considering that air pressure increases less drastically than co2 with temperature increase, a good argument can be made that an 850psi HPA tank is LESS likely to cause a problem than a co2 tank.  IF both exposed to 98F (which is not a terribly unusual temperature), which would stress the tank block mounting system more?

So I'll take the stand that over all (considering all the temperature ranges a gun is normally used in), 850PSI output  air is less stressful to the mounting system than co2.

UNLESS the regulator fails...and they can. Inside there is a spring controled piston kind of per set to only let out a set pressure of gas.  That piston has a seal that blocks the vent from the 3K tank at some set pressure.  But that seal can leak, letting the air pressure creep up.  If it totally fails, then all 3K of air is dumped thought the regulator.

There is a burst disk (a safety feature, kind of like a blow off valve on a hot water heater) on the reg.  Would be good to have that burst disk be a 1.8K one rather than the 3K ones that are often used.

I may be paranoid, but will also use a RAP4 on off.  Does have a gauge to read the output pressure (which can help diagnosis creeping pressure from an almost-sealing regulator) but it also has a burst disk.  That way, can put two 1.8K burst disks between the 3K tank and the gun.

[Ribbonstone]

Know of no tests made of the real strength of QB tubes.  Suspect that the type of steel and heat treatment has varied over the years.  Some may expand and contract slightly as pressure is applied (which is expected), some may expand and deform (not contracting again), and some may just fracture.  Can be soft/ductile or hard/brittle; we assume they are all safe with co2 type pressures but have doubts even the Chinese ever did any real testing (the quality control of sub contractors would have to be constantly checked).

So basically, while an individual can investigate an individual QB tube, what they find probably doesn't hold true for all QB tubes.  If you have to set a limit, would have to set a low enough limit that lets the worst examples survive.

Pressure is pressure, co2, air, or aardvark farts...if it fails at 1000psi with one, it would have failed with any of the others.

[Motorhead]

Very well said ... pressure is pressure !!

Original question on Hot rodding for .22 safely within guns Co2 design parameters still stands ?

Know of no tests made of the real strength of QB tubes.  Suspect that the type of steel and heat treatment has varied over the years.  Some may expand and contract slightly as pressure is applied (which is expected), some may expand and deform (not contracting again), and some may just fracture.  Can be soft/ductile or hard/brittle; we assume they are all safe with co2 type pressures but have doubts even the Chinese ever did any real testing (the quality control of sub contractors would have to be constantly checked).

So basically, while an individual can investigate an individual QB tube, what they find probably doesn't hold true for all QB tubes.  If you have to set a limit, would have to set a low enough limit that lets the worst examples survive.

Pressure is pressure, co2, air, or aardvark farts...if it fails at 1000psi with one, it would have failed with any of the others.