Mountain Air .25 cal. QB78
Built on a QB78D, the outside fit and finish of everything except for the barrel is factory standard. Thatâ€™s not a bad thing. If you havenâ€™t held or even seen the current versions of the QB78D, theyâ€™ve improved. Metal work is as well polished and evenly blued as any gun on the market, the stampings are gone, being replaced with silver lettering, and the stock is almost graceful.
BE AWARE...ROY had NOTHING to do with that muzzle attachment....that bit of ugliness is all my fault.
The new .25 cal. barrel, besides being longer (24â€), is finished in a very nice soft satin blue. Thatâ€™s the only external evidence that the rifle is other than a standard 78D.
Roy does a very nice shroud, and I suspect most of his orders include one. Have been making my own for a good while, and decided that I wanted something quick detachable for this rifle so ordered it without one of his shrouds. Want this rifle to hunt with, so simple is a positive.
Itâ€™s a long wait. Roy has more work than time, so expect 4 or 5 weeks wait for your name to come to the top of the list, then a week (for a simple job) or three (for a fancy job), and some shipping time....call it 6 to 8 weeks.
What I expected was a rifle able to toss light weight .25â€™s to about 600 and heavy weights just over 500. I really UNDERESTIMATED Royâ€™s tuning and valve work.
This is a bulk fill rifle, but for most testing it was run from a remote line connected to a 20oz. tank.
Diana Rastatt - 19.4gr. - 671 fps -19.4FPE+
#3 buckshot - 23.3gr. - 603fps - 18.8 FPE+
Ram Jet - 24.2gr. - 603fps -19.5 FPE+
Spitz Kugeln - 25.1gr. - 601fps -20.1FPE+
Crow Mag. - 26.2gr. - 596fps -20.7 FPE+
Ram Point - 27.1gr. - 594fps -21.2 FPE+
Kodiak - 30.7gr. - 584fps - 23.2 FPE+
To be truthful, really was not expecting the rifle to be that fast. Looks like a normal (although long barreled) QB78D, but certainly moves more co2 with every shot. Bolt runs smoothly and without any more spring resistance than a standard QB78, so what is done to get the gas to the pellet doesnâ€™t require a heavier than normal hammer spring.
ITâ€™s the valve and transfer system. Without giving royâ€™s techniques away, he changed the valve geometry, produced a new valve seal, and smoothed/enlarged the gas passage. Not just more gas being released but gas that flows with much less restriction. Most of the other tune work was done as well. Canâ€™t judge how smooth the issue rifle was on the inside to start with (judging from the outside, it started life a lot smoother than my older QBâ€™s) but it certainly is smooth now.
Some testing showed that it takes about 1.1 to 1.2 grams of CO2 per shot to move that Kodiak pellet to 23 foot pounds. Thatâ€™s about 2 1/2 times as much gas being used per shot than an out-the-box QB78. being a bulk fill, it carries a bit more co2 than one that runs on 12gr., but not a whole bunch more. Can figure about 22-23 good shots per ounce (28gr.) of co2. That would let a 20oz. tank last for about 430 shots and a full bulk of the gas tube (about 1 1/2oz.) last for 33 shots. Most bulk fills under field conditions are less than full, call it 7/8oz. for about 16-17 full power shots.
The barrel work is top notch. Not just the finish (which is excellent), but the machining. Crisp cuts, square where it should be square and well rounded where thatâ€™s called for. Barrel is very slightly larger in diameter than a standard QBD barrel, enough that the barrel band shows signs of being lapped to fit (a nice touch).
The bolt probe is of the same design as the standard QB, but larger in diameter, with larger passageways, and using dual o-rings for sealing. Iâ€™d have to take the o-rings off to see how it was made, but evidently the original probe was cut off and this probe added to the stock bolt. Do not know if it was welded on, silver soldered on, or threaded, but once the o-rings are off how it was attached should be evident. The bolt work is excellent.
Sighting in and initial accuracy tests were shot at 25 yards. The two heavy pellets both grouped great, as well as the light weight Rastatt. The overall best groups were made by Kodiak pellets. Kodiak averages for three 5-shot groups at 25 yards is just over 1/4â€ (.27â€). Thatâ€™s reasonably small for any size pellet, but with a .25 itâ€™s just an oblong hole. In fact, the only pellet that groups less than great was the Ram Jet (but the ram point was close behind the Kodiak for 2nd place).
Didnâ€™t test all the pellets at 50 yards due to lack of time and impending rain. Besides, if the pellet shot poorly at 25 yards, doubling the distance isnâ€™t going to make it better. The overall winner is the Kodiak. Not only shot the smallest 50 yard groups (three 5-shot average is .87â€), but really seems to drift much less in the wind than I expected. For 3-shot fans, kept track of the first 3 shots in each group, and those would average about .68â€.
Round ball (Hornady #3 buckshot) didnâ€™t group as well as any of the pellets at any range. Itâ€™s useful for short range (Iâ€™d keep it inside 20 -25 yards to stay under 1â€ ). The only real good things to say about round ball are:
1. Itâ€™s cheap and easier to find than .25 cal pellets.
2. Even in pitch dark, canâ€™t load a round ball backwards.
3. Not having a front or back, it canâ€™t tumble.
As a hunter, this rifle has a lot going for it. More energy than needed for airgun type small game (rabbits, tree squirrels, pest birds) but it certainly has the accuracy.
Head to head shoot-off with a .22 Discovery.
Had a little shoot-off at 25 yards, Six 5-shot groups for each rifle, each using the most accurate pellet found so far (Kodiak in the .25 and Crosman premiers in the Discovery). the better pellets were tested again at 50yards.
The Discoveryâ€™s 838 fps average (in the sweet spot between 1750PSI and 1050psi) with a 14.3gr. pellet works out to 22.3 foot pounds. This is just about even with the QB 25/78Dâ€™s 584 feet per second and 23.2 foot pounds.
The Qb 25/78D is more accurate at all ranges tested. Discovery can beat 1â€ at 50 yards, but the AVERAGE groups size (5-shot groups again) is closer to 1.2â€. The trigger of the Discovery has been worked over, but itâ€™s not as good as the QBâ€™s and the light weight of the Discovery does not steady it from a rest as well as the QB.
That .25 pellet drifts in the wind just about the same as the faster .22 pellet. Ballistic programs actually show a tiny bit less drift for the .25, but itâ€™s so little can ignore it.
The .25 has a bit more energy at 50 yards due to the better BC of the heavy , well shaped Kodiak pellet. Itâ€™s not a great amount, and either one of them have more than enough power for game at whatever range accuracy limits your shots.
The higher velocity of the Discovery .22 gives a much flatter trajectory. Bullet drop for the .22 (both rifles zeroed at 30 yards) is less than 1/2 that of the .25. That is an important difference when hunting; guessing the range wrong will more often result in a miss from the slow .25 than from the fast .22.