HPA

[ribbonstone]

Why HPA and not CO2?
1. Not nearly as temperature sensitive.  You can use HPA in the middle of winter and get the same performance as room temperature.
2. Power can be boosted or lowered by changing the regulator pressure.
3. Delivers the same air pressure to the valve with every shot.
4. You can fill them at home, even when your co2 bulk tank is empty, with a hand pump (or a high pressure air tank).

HPA vs PCP:
1. More shots per fill with typical QB/HPA, but more pumps (if using a hand pump) to reach a fill.
2. HPA gives a consistent gas pressure gives a long shot string of small vel. variation.
3. The rifle itself never has to contain truly high pressure air; the pressures can be no more than co2 normally achieves.
4. PCP’s can certainly be set for higher energy levels, but not for nearly as many shots per fill-up.

The low temperature sensitivity and longer consistent shot string is what attracted me...still does.  Even with a small 13 CI air bottle, getting 75 shots at 13 foot pounds that don’t vary by more than 8 feet per second, or 45 shots at 25 foot pounds that won’t vary by 10 feet per second is impressive.



These two converted HPA QB78’s have become my favorite hunters.  Yes, they’re heavy. Complete, ready to go,  the shorter QB78/5mm runs 8 lbs. 4 oz. while the longer QB78D/25 runs 8 pounds 11 oz so neither one of them is a light weight.  The 5mm is set to run at 13 foot pounds b (14.3gr @ 640 fps) while the .25 can make 25.6 foot pounds (30.5gr. @ 615 fps).  This is about 8% more energy than they get on co2 during the summer. Both are running on HPA 13 CI bottles regulated to 850 PSI; if you are power hungry, can add  about 10% more energy if regged to 1200 psi.

Running from 3,000PSI to 1,ooo PSi, the .20 will give 75 shots (975 foot pounds per fill) while the .25 is a gas hog, getting 45 shots from 3,000psi to 1,000PSI (1152 foot pounds per fill).  Depending on the pellet used, either of them can shoot their whole shot string with  much less than a 2% variation (and 1.5% is not unusual).

Converted by shortening the gas tube, adding a QB79 gas block, inletting the stock for the new gas block, moving the barrel bands to behind the gas block,and adding the supporting stock screws (also glass bedding the gas block to the stock for added support).



If you can do the work yourself, could easily pick up a decent used QB in .177 ot .22, the gas block, HPA bottle, and be on the cheap side of  $175.  With the shown On/OFF( a RAP4 with gauge) call it $200.  Would be even cheaper (and no stock work, drilling, or tube work) to start with a QB79..and there is no reason you can’t use co2 when the weather is hot.

This was from the Qb78D/.25 , but shot at the odd distance of 22 yards (when it rains, that's what I can get without getting soaked):

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BTW: If you lose your nipple cover, the little snap-on part of one of the mini-marks-a-lots snapes onto the nipple just fine (it’s ugly, but fills the need for a nipple cover until you can buy one).



Also, this picture should give some members the idea...if you really hate removing the safety in order to de-stock the metal work, you can fix it so that you'll never have to take the safety out again (unless working on the internals of the trigger).

[London177]

That's the way to go Rib without a doubt. Thanks for the info' and photos. You've done some exceptional work with the QB's.
regards,
Alan

[johncedarhill]

Excellent work and description. Maybe when I run out of chores I can try that on my qb 78d.

[Jaymo]

I've been thinking about doing that to my QB79. I'm assuming you relieved the inside of the stock so the safety will pass through it.

[ribbonstone]

Also thinned the safey's thickenss (so the inletting slot could be smaller), then pinned the safety so that it points straight down when off safe.  That changes it to a 90degree rotation, which you can flip in or off with your trigger finger.  

Have to check your rifle...most of them are fully off safey when the safety is pointing down, but some of them need a flat filed on the drum at that point  to fully disengage the safety.

[BigCat1]

What brand or reg and bottlers are you using...............and what is the highest pressure to use  safely.,.........................Thanks Troy

[ribbonstone]

The gas tubes are only designed to hold co2 pressure...so anything above 1000SPI would make me want to add two valve restaining screws (as issued, there is one screw).  CO2 can go higher than 1000PSI, but better to consider that the max. for the standard gas tube.

Some people are running 1200PSI, 1400PSi,and even 1600PSi, and if they've reuptured a gas tube, they're not posting about it.  Have been some posters that have had valve problems at that level.  


Could cnage the gas tube to a PCP rated tube (they are some custom shops that make them), but if going to that bother, make the rifle a PCP and be done with it.

I would add two valve retaining screws if going above 1000PSI.  Personally, am keeping those two at 850PSI as that's as fast as I need them to go.  A little faster than warm weather co2, but will give me that speed in the middle of winter. Even at 850PSi, am considering adding two valve retention screws.....hasn't been a problem, but like to have the added solidness.

Regulators are pre-set. They can be adjusted, but it's a matter of changing the spacing of the spring washers that run them and that's not something to fool with unless you know what's what.  Consider them fixed, order the PSI you want for the start.

Are not stamped with a logo, the bottles from three sellers all seem to use the same regualtor.  Looks a lot like the Myth regulator, but as I've not compared the insides, can't tell you if it is the same.

[Gene_SC]

Excellent comparisom and dang good straight forward information Rib. All you need now is one of them custom rotary clips and you can really spit out the lead.

Thanks so much for sharing this. A great post on HPA vs CO2 configurerations on the QB's

Gene

[jonny1o1]

im definitly seeing the advantages of HPA would a 13CI tank with a crosman pump be alright for HPA?

would the tank really need to be pumped to 3000PSI, or would refilling to only 2300 PSI or around there be good?

[ribbonstone]

Will store the tank with about 1,000PSI in place.  90% of the time, will pump the tank up to about 2000PSI-2200..which takes about 55-60 strokes on the pump...which is where I tend to take a pump-cool down rest anyway.  Some times, will go make a cup of coffee and drink a couple of sips...then pump it another 50 strokes....take a pump cool down rest and finish my coffee...then top it off to 3,000PSI.

So long as the pressure is a good bit higher than the regulator'sout-put, it will shoot just fine.  Am running 850PSI , so will stop shooting at 1,000. that would give me from 3,000 to 1,000 psi for shooting, which gives between 75 shots (a .22 set to 11.3 foot pounds) and  35 shots ( a .25 set to 25.5 foot pounds).


Finsished testing these three. Still warm here, so reconverted them back to CO2 until winter months.  Left to right: .25/.22/.20


Been adding this when posting about HP.

Safety concerns:

Has been a lot of discussion about using QB gas tubes for HPA.  SOME of those concerns would be minimized by using HPA pressures regulated to be about equal to  normal temperature co2 (850psi).  So long as the QB’s tube pressure doesn’t exceed normal co2 pressure, there shouldn’t be a problem.  I’m still not convinced that running an HPA regulator to anything over 1050-1100PSI is a great idea and much prefer to run at a conservative 850PSI.

Air is “thinner” and will find a small leak that often goes unnoticed when using co2. Co2 also tends to expand o-rings (the o-ring absorbs some of it and swells).  Expect to do a bit of leak detection and o-ring replacement (better to use better quality o-rings) when switching to HPA.

There is still the possibility of a regulator failure and all 3,000PSI being dumped into the tube.  the burst disk on the gun-side of the regulator is a 1800PSi disk...it should let go if the regualtor fails and vent the excess gas.  Doubt the gas tube would shatter like a grenade, but would expect the internal parts to be over stressed and fail.

[Jaymo]

Very good write up, Rib. As always.

[ribbonstone]

Know winter is coming, even down here in the "sweat lands" can feel the coming changes.

So, off with the CO2 on at least these three, on with the 850PSI HPA tanks, and an afternoon resighting....ready for  cold weather tree squirrels (although the two hurricans did a lot of damage to the acorn/nut crop).

Left to right: .25 / .22/ .20