Canadian Airgun Forum

Some of you might remember my post about a home made air rifle that I built some time ago. It shoots arrows and steel 3/8" 55 gr steel balls. Recently, I discovered it is the perfect fit for a 357 magnum shell. So I removed the primers, drilled it out and loaded them with 50 #7 1/2 shot. It works perfect as shotgun shells. Nice pattern and 600 fps avg. The bb,s go through 1/2" drywall at 15 yds. Perfect for starlings in a barn. Today My friend Watertown dropped by with a 24" .22 cal crosman barrel that he made a breach and scope mount for connecting it to my steel ball gun. Well here are some numbers I got. At 600 psi, I avg 775 fps. At 725 psi, I got 844 fps. And very accurate out to 50 yds. So now I have an arrow gun, a shot gun, a round ball gun and a pellet gun, all in one gun. I will be looking for a 357 rifled barrel for it later when I can afford it. Sorry, no pics at this time, but I will later.

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If I had only one wish, it would be to be able to "unsay" things.

I forgot to mention that the air reservoir was 2.2 ci and it dumps all of it each shot. Just now I down sized the reservoir to 1.5 Ci and got the same results.

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If I had only one wish, it would be to be able to "unsay" things.

WOW - good performance, Joe - keep at it!

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Best Wishes
Daryl

Thanks Daryl. Now that I have proven the effectivness of low pressure, high volume in a prototype, I intend to build a real gun with a real breech and trigger. Right now it,s quite makeshift. Since I can nearly schieve the same speed with 55 gr steel balls, Im assuming I can launch heavy pellets as fast . So thats next on the experimental list.

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If I had only one wish, it would be to be able to "unsay" things.

Sounds really KEWL, Joe!....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

I want to build one with a built in reservoir and regulator. That way I can open a valve, and the pressure chamber automatically only fills to what ever pressure I set it. Then close the valve and shoot. I would have to manually open and close the valve each shot, but that would be considerably faster than pumping 10 or 15 strokes with a hand pump every shot. Thats why I was looking for a connector hose to use an AT44 tube as an external reservoir.

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If I had only one wish, it would be to be able to "unsay" things.

Brilliant experiment, Joe. You seem to be progressing nicely from imaginative innovation to practical application. I'm anxious to follow your progress.

Excellent achievement & ideas, Joe - on the road to victory.

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Best Wishes
Daryl

I test fired a couple of 25.4 gr pellets . At 500 psi I got 571 fps. And at 600 psi I go 700 fps.
Even better than that. I tried the 16 gr pellets at low pressure of 250 psi and got 560 fps avg. one shot might have had closer to 300 psi but it went 584 fps.
What might this mean for big bore air guns ? Well, if a reservoir with a metering and regulated valve system was used, then there would be a few advantages . Using my dump valve, there would be no need for a powerful hammer and spring, each shot would have the same ammount of air at the same pressure, so a flatter shot string. A 3000 psi 500 cc reservoir should produce over twenty shots on a fill, because there would be more useable air, down to 600 or 700 psi. And Im assuming higher pressure, but less shots per fill could go super sonic.
Theres a facinating range of options to be tested. Not to mention ammo types. IE: Arrows, shotgun loads and bullets from the same platform.

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If I had only one wish, it would be to be able to "unsay" things.

The secret to efficiency with dump valves is not getting greedy.... It is the ratio of valve volume to barrel volume that is important.... The maximum potential FPE is a function of the barrel volume and the pressure.... For a given barrel volume, the larger the valve the closer you can come to that number, but the more air you blow out the muzzle after the projectile has departed.... The smaller the valve, the less power, but the higher the efficiency.... It is a matter of coming up with a compromise to achieve your desired results, that you can live with on air usage....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Totally agree with Bobs statement as to a balance.

There are those of us that are following your build there Joe. Considering the concept of low pressure/ high volume dump valves have been around for a couple centuries within the airgun design and development. Not a new concept but one that has been rekindled by technology and generations of those seeking experimentation such as yourself there Joe. Congrats upon that.
Its does bring to mind more recent yet unfortunately commercially built rifles of modern past. Bowkette, Titan, Daystate, all unfortunate builds that fell to the way side as failures no matter the builders or marketing. Not to pee in anyones pot, just rekindled reallity here.

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May the cry of the pack be with you upon your hunt

Whitewolf

I know theres a balance between barrel and volume of air, but the barrel is interchange .22 cal to 3/8" id shotgun barrel. So the volume would have to be adjustable as well as the pressure. Not that it can't be done, I just don't have the resources. Or the smart,s.

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If I had only one wish, it would be to be able to "unsay" things.

Perhaps more practical then, to have a couple of sizes of valves, one for .22 and .25 cal.... and one for .35 cal and arrows?.... You could even make just the larger size, and use a piece of plastic (or metal) as an insert to reduce the volume.... Just a thought....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Thats what I have done now. In fact, I have tried reducing the volume lower, but the speed dropped of rapidly once I went below 1.5 CI. I haven't tried the 55 gr steel balls with the 3/8" ID barrel with 1.5 CI, but I expect a much reduced speed than with 4.2 CI which is the original size.
I was wondering if the reason dump valve guns aren't sold, is because there wasn't an effective valve available ? Or a cost efficient one. My valve design is both simple and very cheap to build. Also it works flawlessly. Since I have proven that 1.5 CI of air at 500 psi, is all I need for decent pellet speed, I can shorten the reservoire by 6" and that would mean I could thread an a AT44 cylinder, directly to it. Since my cylinder is already regulated, I only need a shut off between the AT 44 tank, and the 1.5 CI pressure chamber. Probably a cam that pushes the pin on the AT44 to open it and close it. That way I could still remove the tube while it,s still got air in it.I know theres a way to calculate how many shot,s I'd get from 3000 psi down to 500 psi, but I don't know where to start. I'll have to think on it a while.

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If I had only one wish, it would be to be able to "unsay" things.

If your valve is 1.5 CI, and you are filling it to 500 psi (34.5 bar), you are using (1.5 x 34.5) = 51.7 CI of air (at 1 bar) per shot.... In most PCPs, that would produce more than 50 FPE of energy, but with your low pressure you are unlikely to get that.... However, I digress....

Your Hatsan AT-44 cylinder starts off with 180 cc (11 CI) of air, but you need to subtract the volume of the regulator.... I'm guessing that is about 1.5" long, which would be 1.3 CI, leaving you 9.7 CI of usable volume.... If you start at 3000 psi, and end at 500, that is 2500 psi usable (172 bar), so you have (9.7 x 172) = 1672 CI of air available.... Divide that by 51.7, and you get 32 shots....

You are getting 571 fps with a 25.4 gr. pellet, which is 18.4 FPE x 32 shots = 589 FPE total energy per fill.... That works out to only (589 / 1672) = 0.35 FPE/CI.... which is about 1/3 the efficiency of a Hatsan AT44.... You can do similar calculations for the other combinations of projectiles and valve volumes....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!