Alternate QB79 HPA post ("Stumpy" the 100 foot airgun)

[Ribbonstone]

With cool weather coming and the interest in HPA/QB’s, might be time to look at “stumpy” again.

Not the only HPA/QB in the safe, but the QB .22 is the simplest.  If you were happy with typical co2 type performance in the summer (just a little bit better than “stock, something like 12-14 foot pounds), can have that in the winter with HPA and MINIMAL $ outlay.

Came to the conclusion that if you are going to own many airguns, then not all of them should be really powerful ones.  Better if each one has a use they are really-really suited for. Find much more daily use for the lower powered versions than I do daily use for the hot rods. When you need power, there is no good substitute, but when patrolling a typical back yard, excess power is actually a disadvantage (both in noise and in added penetration).



Stuff to do:
#1. 850PSI 13CCI bottles are cheap and 850PSI can more than equal co2 performance.
#2. Standard valve actually works great on air at 850PSI…probably LESS likely to blow a valve seal than co2 as (a.) the pressure is less than summer time co2 and (b) air is less “dirty” than co2 and (c) becomes a closed system (in that the tank doesn’t go on and off to fill) so less likely to pick up stray grit/dirt that can slice your valve stem.
#3. Can get +200 shots per fill at that energy level.  That does take a little fiddling around, but very little compared to the power tunes.

Am going to repeat #3 as it is the main reason I keep this rifle as it is. Same co2 power/ +200 shots per fill/ doesn’t seem to care how cold it is outside. 

Did do the following:

1.   Cut/crown the barrel to 16”.  That RWS “compensator” doesn’t telescope over the barrel very far, so it looks longer.
2.   Added a cheap 850PSI output 13CI tank.
3.   Mounted an old Tasco 3-9X just because it was lonely and I wanted the 4X that was on it to use elsewhere. Did mount it as low as I could as the QB79 stock doesn’t have much of a cheek piece.
4.   Changed the transfer port to a poly tube.
5.   Valve is ALMOST as issued. Old valve still have that horrible little fiber filter/screen filter, which has shown itself to just disintegrate and foul the valve.
6.   Adjusted spring tension (decrease) the old school way by removing it and cutting ½ coil at a time until I got down to 12-13 foot pounds.
7.   7. I got use to using the gauged brass on/off, but you can leave it off.  Could cut the barrel back another 1.5-2” without it and make it even more “stumpy”.

So even set up for minimal air use, still see a little rise in energy for heavier pellets. Still in the 12-13 foot pound ball park, with the lightest (RWS Hobby) earning about 12.2 foot pounds and the heaviest tested (18.1gr) earning about 12.8 foot pounds. 


ACCURACY:

This won’t win any bench rest competitions, and perhaps shortening it to 16” actually helped it shoot well, but its “good ‘nuff”.

20 yards/ 5-shots each:


Do have enough airguns (more than enough if you ask my wife), so they kind of take on tasks.  The task this one is best suited for is rat-zapping/suburban back yard pest defense.  It’s short, really-really quiet (big LDC/ lower power/ small air use pretty much equals real quiet), accurate enough, and LESS likely to blow holes in my outbuildings (and if the rats are out in the shed or the shop, why would I want to shoot them?).

Not real sure I’d ever try shooting anything alive past 35yards…probably could get lucky at 40yards, but the trajectory makes things “iffy” much past 100 feet (which is why the title).

TRAJECTORY:

SERIOSULY…really expect a flat trajectory from 650fps/13.4gr.?  Not going to happen. Wouldn’t happen with co2 as the gas, won’t happen just because air is the gas.
Can mitigate it a little, depending on scope mounting height, with the traditional 30 yard zero.  That would put you about ½” high at 20yards and about 2/3” low at 35yards, which covers most suburban back yards just fine.



Something like 8.4-8.7 foot pounds left at this range, so I’d not try it on anything tougher than a small tree squirrel/rat.

SOME THINGS: I DO NOT KNOW WHY:

FIRST: Know the theory/practice of free floating and I tried it.  The tank actually does NOT touch the barrel, although it will “clank” when carried roughly. 


For this rifle to shoot, I NEED a little barrel pad between barrel and tank.  I’d have thought that would have screwed up accuracy, but for whatever reason, shoots better with that soft pad (of friction tape) than it does without it.



Considering the old adage, decided not to play orthodontist to a gift horse and just accept that it “is what it is”.

SECOND: When I decided to shorten than QB79 barrel, ran a few tight patches though it. Thought I detected a slightly tight spot at about 16”.  Put a couple of rod-pushed pellets though the bore and still got the impression that there was a little tight spot at about 16”.
So I cut it at 16”.  My thought was that if there is a tight spot in the barrel, would be better if it was at the muzzle than in the middle.

Have no idea if this helped or hurt accuracy,  but suspect (from use) it didn’t harm it any.

SHOT COUNT;
Does seem to take forever to both chronograph and shoot 43 5-shot groups.



Didn’t read a real drop in velocity until shot #206.

Velocity very uniform for unsorted pellets. Even the worst individual shots fell inside 2% (and out of 215 shots, have to expect a few odd-ball pellets).
So I’m not guessing/estimating/predicting +200 shots, have actually produced them.

COST:

Let’s assume you can change to a polly port, adjust mainspring tension, cut a barrel, and recrown a barrel (which would make those four jobs “free”).  Then you would need to put out $ for the following:

QB 79 about $106 (buyt if you are reading this, probably already have a QB79...and likely from the days when it cost $80-90 new).

$60 850psi 13ci bottle. Lots of places on line, and there are more sophisticated bottles, but the simple (cheap)800- 850Psi output tank will more than duplicated co2 speeds.

$40 RWS compensator (this one taken from an RWS 850, but it fits the QB barrel just fine).  Can look on-line for information to “activate” the brake.
 So you could do-it-yourself for about $206 to end up with a short 12-13 foot pound really quiet carbine with an afternoon or two invested.

Could buy a $270 for a ready to go  version from a well-known dealer (I forget which forums where that name is forbidden), take it out the box and do NO WORK and end up with about 13-14 foot pounds… but it’s louder than optimal and full length.  I’d estimate something like 125-140 “good” shots with that out-the-box set up.

 HIDDEN COST: 3K filling Filling

The hidden cost is a way to fill the 13CI tank.  My answer is a pump. To date, the 3 pump brands I’ve had no trouble with have been FX, Hill, and the cheap Chinese pump from Flying Dragons. To be honest, filling from 900psi (about where the 800-850psi tank start to go off reg) to 3K is a PIA.  But for 200shots, have to expect some effort. The way I use this rifle, one fill, just taking 20-30 shots a day, lasts a week.

More likely for me is to shoot that rifle just a few times a week (usually only at garden pests or when there is a rat infestation under my shop/shed) so one fill lasts a month or two of actually “fired in anger” usage.

Not for everyone, certainly not for the power hungry, but if you’ve got a typical suburban back yard, it will cover the distance.  If co2 had been doing “it” for you in the summer, HPA can do “it” for you in the winter with not temperature problems (OK…you folks that have to live though -20F in the winter…I really don’t know how that would mess with seals/regulator/etc. Generally, once it gets under 25F, I stay inside.)

[SpiralGroove]

Hey Ribbonstone,
Nice work . The QB's are easily the best bang for the buck (cost/quality) in a PCP; especially if you can do the work
Looks like you're ready for some serious, cool weather patrolling of the backyard.  Everything the size of a dime should be on Red ("Ribby")Alert .  After all, you've got 200 chances to bring home the bacon .

[Gertrude]

Great Post and Great Info !
Thanks Ribbonstone !

[mercury]

Interesting post , I will take note of the tip re barrel pad thanks

[beerhippy]

You've got that well sorted.  Good job!

[Ribbonstone]

Once I realized that something like 200 shots at 12 foot pounds was possible, it kind of overshadowed the urge for power. Got to thinking of "stumpy" for different uses (whenever the target is 30yards out or less and the need for real quiet is important).

[WeeHeavy]

Great stuff! Nice break down of the project and costs. I love reading posts like this. They get me dreaming of the stuff I hope one day to have time and money to do.