GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on July 22, 2015, 05:08:03 PM
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I had somebody contact me this morning to ask how to build a .30 cal Springer.... I have never seen a complete analysis of springer designs, but my gut reaction was to tell him to make the swept volume proportional to the FPE level he wanted.... I just had a quick look at a few volumes for some common springers, and if you take the volume in cc's and divide by 3, you get the following numbers.... Individual guns may be a bit higher, but the numbers look pretty close to me....
Crosman Quest / Gamo CFX/Whisper - 49cc / 3 = 16.3 FPE
Weihrauch HW95 - 45 cc /3 = 15 FPE
Weirauch HW80 / Beeman R1 - 57 cc / 3 = 19 FPE
Diana 350 - 71 cc / 3 = 23.7 FPE
Hatsan 125 - 80 cc / 3 = 26.7 FPE
Webley Patriot - 81 cc / 3 = 27 FPE
Hatsan 135 - 87 cc / 3= 29 FPE
So for a .30 cal, if you want 700 fps with the JSB 44.8 gr. pellets that is 48.7 FPE x 3 = 146 cc of swept volume should be about right.... To get 850 fps (72 FPE) make that 216 cc.... :o
Bob
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Holy Moly!!
:o
What kind of spring, Gas or Wire, would one need?
Say the coils off the rear of a Suburban?
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Different problem, but yeah, I wouldn't want to have to cock it.... ::) .... Maybe the biggest, meanest Gas Ram you can find at a place like N-Forcer?....
Bob
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Cocking it would be the small problem.
Given the size and weight of this fictional thing?
I'd think a permanent gun mount would be needed.
;D
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This would be a very heavy gun!!! Just think of how beefy the stock will have to be for this gun to deal with the recoil.
Oh yeah and try and mount a scope to this thing.
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I'm thinking it would look something like this?
(http://i108.photobucket.com/albums/n12/privateer_2006/12pdr-Saturday-28.jpg)
;D
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LOL
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Wait I'm confused about those figure for volume...
I'm assuming swept volume means the volume of the compression tube length that the piston travels. On my Vantage I know only moves about 6" and the diameter is 1"... That comes out to about 12 cubic centimeters, not the 49 you quoted for a Quest which I assume is the same.
V = pi * r^2 * h
4.71 = pi * .5^2 * 7
4.71 ci
* 2.54
= 11.9 cc
Edit
Nvm apparently you can't convert cubic inches to cubic centimeters like I was trying
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I had somebody contact me this morning to ask how to build a .30 cal Springer.... I have never seen a complete analysis of springer designs, but my gut reaction was to tell him to make the swept volume proportional to the FPE level he wanted.... I just had a quick look at a few volumes for some common springers, and if you take the volume in cc's and divide by 3, you get the following numbers.... Individual guns may be a bit higher, but the numbers look pretty close to me....
Crosman Quest / Gamo CFX/Whisper - 49cc / 3 = 16.3 FPE
Weihrauch HW95 - 45 cc /3 = 15 FPE
Weirauch HW80 / Beeman R1 - 57 cc / 3 = 19 FPE
Diana 350 - 71 cc / 3 = 23.7 FPE
Hatsan 125 - 80 cc / 3 = 26.7 FPE
Webley Patriot - 81 cc / 3 = 27 FPE
Hatsan 135 - 87 cc / 3= 29 FPE
So for a .30 cal, if you want 700 fps with the JSB 44.8 gr. pellets that is 48.7 FPE x 3 = 146 cc of swept volume should be about right.... To get 850 fps (72 FPE) make that 216 cc.... :o
Bob
I absolutely gaurantee you I can hit a hub cap at ten yards with that thing. Sometimes just because you can build it isn't enough reason to actually do it.
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There are (2.54 x 2.54 x 2.54) = 16.4 cc's in a cu.in....
Bob
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Some airgun smith should try to build one of those monster ...just for the kick of it. It would be monstrous, heavy and would be a blast to shoot. Not for commercial purpose for sure, but just as a some kind of personal or marketing project. All the parts can be done, but for sure some smart engineering would be required to cock this thing ...
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Sometimes just because you can build it isn't enough reason to actually do it.
I bet someone told someone the same thing once.
The PCP version of what resulted.
;D
(http://r.ddmcdn.com/w_622/u_0/gif/punkin-air-cannons-08-625x450.jpg)
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I think it's feasible to make one, though the only way I would guess it would work is using two or three gas pistons and using individual levers to cock each piston then the trigger mechanism would release them at once. Wouldn't be pleasant to shoot though and would be a nightmare to carry.
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Just for fun? The Punkin Chunkers came to be. Now those things shoot punkins a mile?
:o
Given rsterne is the best math guy on all this?
I say we politely ask his advise and skills to assist us to actually build one.
What bore-stroke-power kind of info.
It may only be a mind game? But if things look plausible?
They shoot punkins a Mile.
We're talking a .30 cal lead slug!
;D
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I'm not a springer guy.... but I did look at what it typical for bore to stroke ratios, and they typically run from 3:1 to 4:1, although a few fall outside that range.... The bigger the bore and the shorter the stroke, the more force you need to drive the piston, and the less distance you get to compress the spring / gas ram.... This means higher forces over a shorter distance.... It may come down to what is available, particularly in gas rams.... The longest stroke N-Forcer only has a 125 mm stroke, so with a bit of free play call it 120mm.... If the piston is 40mm OD, that gives a swept volume of 150 cc, with a 3:1 ratio.... That swept volume is towards the bottom end of the practical power range, IMO....
Before putting much effort into this, you need to define a realistic power level....
Bob
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You might be focused on the mini Gas Pistons.
N-Forcer does have bigger with 300 mm stroke up to 7.5 tons behind them.
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So lets say we use a mechanical device to cock and it's NOT a carry Gun.
It would be a solid mount construction. Say the back of a Jeep or something.
We have 300mm of stroke.
The piston only needs to be so big right?
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You might be focused on the mini Gas Pistons.
N-Forcer does have bigger with 300 mm stroke up to 7.5 tons behind them
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You bet I am.... anything with a longer stroke is at least 50mm (1.98") in diameter.... Maybe you can take the time to look through other manufacturers?....
Bob
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Not to mention, it would not be a direct translation of swept volume to fpe. You'd need to determine the best t port size to optimize efficiency, and you'd have to do your darn best to keep the t port as "short" as possible- but you're going to need an aweful thick and sturdy cap on the end of the tube as well. Plus stroke length and piston weight balanced with the force of the spring. If the stroke is too shirt you'll never get enough momentum to hold the piston down against that large volume of air, that thing needs enough stroke length to get moving pretty fast before the pellet begins to move, then pop loose and start moving down the bore at,just the right time. It would take a lot of trial and error, to say the least.
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So lets say we use a mechanical device to cock and it's NOT a carry Gun.
It would be a solid mount construction. Say the back of a Jeep or something.
We have 300mm of stroke.
The piston only needs to be so big right?
I saw,an interesting video on YouTube, of guys shooting bench rest at 1,000 meter with customised bench rifle that weigh about 50 pounds and up. I think this would be the extreme bench rest of air rifles. I imagine a sledge system like the d48, only with a much much bigger and heavier stock and action as well.
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You bet I am.... anything with a longer stroke is at least 50mm (1.98") in diameter.... Maybe you can take the time to look through other manufacturers?....
Bob
Say we stayed with the N-Forcer MF-25 which is a 1" Gas Spring but ordered a custom version?
That is do able.
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Perhaps.... They have one with a 178mm (7") stroke, but there is a warning on the website that says "Limited speed and stroke life".... You would have to contact them for more information.... Part # MF25-178.... It would be ideal if it worked, but I didn't look at it because of the cautionary note.... With a 172mm stroke and a 40mm bore, we would have 216 cc (exactly right for 72 FPE) and a bore/stroke ratio of 4.3:1....
Bob
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Heck yeah. But why? Because 'Murica! You could probably build it as a side lever, with a lever on each side to cock it and a foot stirrup like a crossbow! If I can find that video about the super bench rest guns, I will link it. Probably wouldn't be popular, obviously special purpose, but I,fell like you could realistically make it at around 20 or 25 pounds with a recoil sledge and expect to hit stuff with it.... :D
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with a 2 pound piston and a 2 second lock time?
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The linkage cocking shoes and even the barrel would suffer from the force applied trying to cock the thing. David
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Hey Bob,
My Hatsan 135 in .25 caliber is a Bazooka. I love it, but don't shoot it too often because it's so heavy and has a starling recoil that requires considerable patience. Plus I only get 750 fps from 19.91 H&N's.
My HO is to go with a PCP for any pellet diameter > 22 caliber :D
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I agree 100%, Kirk.... this is NOT my idea, all I'm doing is supplying the numbers for anyone crazy enough to try this.... I see no practical value or use for it....
Bob
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More food for thought.... I used an N-Forcer Red 19mm gas ram in a Crosman Phantom, and it overpowered the gun.... ie I'm sure a Blue ram would have produced the same results, and the gun was miserably hard to cock.... I know others that have used a Blue ram successfully in a Phantom.... That has a force of 100 lbs. uncocked, and about 130 lbs. cocked, and the Phantom has a ~1" (25mm) chamber, with an area of 4.91 cm^2 (0.76 in^2), so that means a starting "piston pressure" at trigger release of 130 / 0.76 = 171 psi., and a “piston pressure” at the end of the firing cycle of 100 / 0.76 = 132 psi.... figures I’m guessing we need to match in a scaled up gun.... Alternately, perhaps we can just use the average force of the ram (115 lbs.) times the stroke of 96 mm (3.78" or 0.315 ft.), for a potential energy input of 115 x 0.315 = 36 FPE.... The gun had an output of less than 18 FPE, so figure a 50% minimum loss....
Let's say we had a 40mm piston with a 172 mm stroke to give us the desired swept volume of 216 cc.... That is 1.57" diameter, for an area of 1.93 in^2, which at 171 psi needs a force of 330 lbs. cocked, and at 132 psi needs a force of 255 lbs. uncocked to give the same “piston pressures".... A Blue 25mm N-forcer ram has a forces of 225-305 lbs. about 10% less.... Using the alternative (FPE) method, the stroke is 172mm = 6.77" = 0.56 ft.... and we have an average force of 265 lbs. x 0.56 ft. = 148 FPE input.... Divide that by 2, and we get 74 FPE, which is close to the target for a chamber of 216 cc.... Looks like the numbers from both methods agree, so it looks like we have a basic design.... use a Blue MF25-178 ram (assuming it will live)....
Now what about cocking it?.... The Red ram in the Phantom was tough to cock but manageable, with an average force of 170 lbs. over a distance of 3.78".... The Blue 25mm ram will have an average force of 265 lbs. over a distance of 6.77”.... That works out to (265/170) = 56% more effort over (6.77/3.78) = 79% more distance.... or a total of 2.8 times the total effort required.... Two levers, one on either side, butt in the chest (on a padded cradle) might do it.... Maybe?....
Bob
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Two levers and a stirrup like a crossbow.
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How about a detachable windlass, like the Medieval crossbows.... *LOL*....
Bob
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Not a bad idea. They put detachable levers on the spring pistols, why not a windlass on a super springer
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With a 12" long handle and a 1" diameter axle, you would have 24:1 leverage, the force on the handle for direct drive on compressing the ram would be 9-13 lbs.... Use a 1/2" axle, only half of that force, and it would only take 4.5 turns to cock the gun.... Build the windlass into a cradle that sat on the bench, and the gun dropped into it for cocking.... Easy-peasy....
For the compression tube you could use 1.75" OD x 0.095" wall CrMoly tubing.... the ID is 1.56" (39.6 mm, close enough).... It would have a 3.8:1 safety margin at 2000 psi.... :o
Bob
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Why not set the buttstock up with a notch or cradle for the windlass, maybe with a detachable cheek piece that slides out so the windlass can slide in, and a cocking slot across the top instead of under neath with a cocking shoe of some sort to attach it to. Similar to a break barrel, the cocking shoe would be slid forward and locked into place before firing. Maybe put some sort of notched anti bear trap like many of the fixed barrels today have, as well. If it were done right it could still look sharp, too. Call me crazy, I think it can be done, and although unwieldy I still think it can be fired from the shoulder...
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Multi stroke...ratcheting rack drive..
Carve notches in the piston...use the sear as a retaining pawl.....each stroke of the cocking lever advances the piston 1 notch.....increase lever ratio by 10 times or more
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Linear Actuator maybe?
Press a button and it would cock the piston.
Wouldn't be a mobile Air Gun but I'm pretty sure we're beyond that already.
;D
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I'm not so sure the gun itself won't be portable, or impossible to shoot.... It should have 4 times the recoil of a medium .22 springer, and about 2.5 times that of a magnum .25 springer.... If the cocking mechanism is separate, there is no reason for it to exceed 10 lbs. or so.... except maybe to tame the recoil....
Bob
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I seen one at the GTA shoot a member here had it (mean machine), the cocking mechanism worked kinda like a old bumper jack, I may be wrong but seems there were 2 power levels on it. David
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Doesn't surprise me at all this has been done before.... in fact I would have been shocked if it hadn't.... Would be nice to see some photos / details, though....
Bob
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So when is somebody gonna take a spring off a large truck and find a scuba tank to serve as a compression tube and build a springer cannon? :-D
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Probably whenever one of us retires BEFORE crossing over to the dark side. Probably not likely :)