A theoretical exploration of physical possibilities, AKA Let's Make A Monster

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Biohazard

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Jan 23, 2016
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Inspired by the recent release of Hatsan's .30 springer and another semi-related thread, a question has planted itself in my brain, and I would be interested to hear the opinions of my fellow airgunners (especially those who have a deep understanding of powerplant mechanics and limitations). Namely, is it theoretically possible to create a viable large-game hunting rifle (meaning .45 or .50 cal, 800-1000 fps) using a spring or gas-ram powerplant? Logistical considerations aside (cost, weight, insane cocking force and murderous recoil), is it possible to produce sufficient muzzle velocity, and how might it be done? If we can come up with a decent answer (and I can come up with the cash), this may turn into a custom-built abomination.
Here are my thoughts on how it may be done: Start with the basic platform of a Hatsan 155 (gas ram, underlever, bolt-action sliding breech, Monte Carlo stock), reinforce the cocking arm to levels heretofore unknown (a rectangular steel bar rather than a round rod, likely knurled for grip), increase the diameter and wall thickness of the compression cylinder (45 mm, perhaps larger?) without lengthening it (unless this is necessary. If I am correct, larger diameter= more power per cycle, while longer stroke= longer shot cycle). I can't help but think the recoil of this thing would make a scope pointless, so I'm thinking a simple set of fiber-optic iron sights. A bench-rest stock might be useful, or at least a mount for a bipod. Weight-wise, this thing is going to turn out 20 pounds bare minimum, and I'd shell out the extra cash (and weight) for hardwood.
Now that you've heard my theoretical musings, I want to hear from you. Is this even possible, let alone wise? If it is possible (or if not and you just want to play pretend), how would you do it? Let's make a Monster!
 
Here are a few to consider.

Insanely powerful crossbows (ballistas) typically use some sort of lever-actuated ratcheting device to cock them. If a powerful nitrogen-filled piston is to be used, a similar device might be a necessity. 

The air chamber will also have to be somewhat larger (think really big piston), which adds to your recoil. Holding the "thing" steady enough to produce a tight group probably couldn't be done. Unless you outweigh the weapon by about 25 times! 

The "pellet" isn't going to be an issue, but boy is that sucker going to be heavy! 
 
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Good points, Alan! I do have a 175 lb recurve crossbow, and I can usually manage to cock that without an aid. That being said, perhaps a ratcheting lock or a longer cocking arm, to gain leverage? I wonder if there is an established equation for cocking weight based upon cylinder size and length of cocking lever. Where did I put that algebra cheatsheet... Although, that also raises the question of the trigger mechanism. I imagine it would have to reinforced to withstand the vibrations of firing, and I am curious if that level of restrained power would equate to an extremely heavy trigger pull. Hmmm...
 
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I've been thinking about how to actually make a big bore springer for a while now. Hatsan pretty much just showed us how far their power plants can be stretched and I don't know of a more powerful production springer off the top of my head. So i guess the next step is to put another power plant in the rifle. And they just did that with their Hercules! The trick will be how to get 2 power plants to work together effectively and not destroy anything associated with/the rifle.

The other thing that I just thought about is barrel length, as in -> what truly is the "best" barrel length? What is the ideal length for velocity?
What is the length for best accuracy?
And how long is too long for practical uses?
 
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I haven't researched the Hercules much, but in theory two compression cylinders (I'm thinking a side-by-side configuration) could have mated outlet ports, so as to funnel the flow into one point. I cannot help but wonder if simply increasing the size of the piston might suffice, since it appears that the .30 Carnivore springer uses the same size cylinder as the rest of the 135 series. From my (admittedly limited) knowledge of physics, the same size piston delivering the same amount of force at the outlet port would produce different velocities for different calibers, due both to the increased weight of larger projectiles and the expansion of the volume of air in a larger bored barrel. To compensate for this, you would need to move a larger quantity of air in the same amount of time, thus generation much higher internal air pressures. You could do this by using two cylinder (an idea which I find very interesting), increasing the diameter of the piston so as to compress a larger amount of air within the same space, or lengthen the piston, so you are pushing a larger quantity of air over a longer firing cycle.
As far as the barrel length, I once read that 24" is about the optimum length for springers. Longer than that actually is supposed to reduce accuracy, due to drag on the pellets and lost force behind it due to expansion in the barrel. Lengthening or widening the piston would obviously alter this, as a greater amount of air is being pushed behind the pellet. I cannot verify this conjecture, as it was taken from reading a rather vitriolic back-and-forth between two reviewers of a rifle. If anyone knows the true answer to this or any other questions of ballistics, please do chime in. I really wish I paid more attention in Physics class now...
 
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Dual pistons would have to be mechanically connected, or one would "overtake" the other, no matter how good the manufacturing part-to-part specs.

I can't speak of nitro piston specifically for airguns, but master units are available for industrial applications. Due to seal considerations, there is a limit, but I don't know exactly what that limit is. I do know that compressed strut ratings exceed 1,000 pounds. Of course they're as big as your arm! 

I do hope you have relatives, because by the time you get it built, it'll take three men and a boy to carry it! While that is an exaggeration, we have to assume your planning on "holding" t in your arms while you pull the trigger?

Oh! Speaking of which... Multi-sear triggers aren't a problem, but you may have to built your own big enough to do the job. 

Good luck.
 
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Tom Gaylord over at PA has a dual piston rifle, a Whiscombe JW75. It is an under lever for cocking (three strokes) it is a break barrel for loading. It uses gearing to cock both pistons at the same time. The opposing pistons, according to Tom make a springer shoot like a PCP. You need to go look at Tom's blogs on this gun to get all the info.

I was thinking if you started with two Hatsan's , Eng. degree, CNC machine, and a little help from Mr. Whiscombe you just might get your monster.

Best of luck,
Noel
 
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Sometime back I had the idea to make a springer cannon---wheeled carriage and all. I was looking at some steel tubing that had an inside diameter of three inches for the barrel. Then looking at some truck suspension springs gave me the idea for the springs. A long ram hydraulic jack for cocking the thing. Some other larger diameter tubing that the springs would fit into for the cylinder. And, . . . .

The stumbling blocks---nowhere near enough time, money, or facilities to make the thing. 

As far as what you need to calculate is just a matter of scaling everything so that you wind up with the same pressures at the port as a smaller rifle. Your projectiles will need to have similar weights relative to a round ball as the smaller guns. That is, if the pellet weight is 1.4 times the weight of the same caliber round ball, then that is the proportion you want to use for your big bore. 
 
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"jps2486"I have a better idea. Let's start with a spring from a car's front end, a piston from a Pratt & Whitney R2800, a flag pole to cock the thing, and a 5 inch barrel from a Navy destroyer. We can shoot Isis ragheads from 5 miles.
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Well, let's see how your numbers work out. A single P&W R2800 cylinder has a displacement of 175 cubic inches. A five inch 38 caliber naval gun has a volume of 3730 cubic inches, and a single car strut spring will not have nearly enough energy to get an approximately 40 pound pellet to travel 5 miles.

(Note: Naval guns and artillery pieces are often defined by the bore diameter (caliber) and the barrel length in how many calibers long it is. That makes the 5" 38 caliber gun barrel 190 inches long. This proportion is quite useful in predicting how a particular gun design will perform with respect to velocity for a given pressure and projectile geometry.)

Now what might be practical to make. Let's start with a 7000 grain (1lb) pellet with a diameter of 1.875" ( 1--7/8"). Put this out at a velocity of 850 ft/s. An RWS 48 in .177 has a barrel length of about 90 calibers long, and it achieves the desired velocity with a similarly proportioned pellet. This gives the 1.875" diameter bore a length of about 168 inches or 14 feet. 

Now we need a piston that has a proportional volume to that of the RWS 48. This I do not know, nor can find quickly. If anyone knows then please add this information. We also will need a spring or series of springs to achieve the same pressure behind the pellet. The pressure is something else I do not know.

Dual pistons connected together would be beneficial. One thought I have (since this thing would be pretty long) is to have one larger piston that surrounds the barrel, while the other smaller one is behind the breach. Both would have the same effective piston area, travel distance, and springs. The difference in piston area is only due to the outside diameter of the barrel. The larger piston would have both an outer and inner seal. 

Since the thing would be an artillery piece, the recoil should be absorbed by a spring system on rails. For that is what we strive to do with our artillery hold on spring powered air guns.
 
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Inspired by the recent release of Hatsan’s .30 springer and another semi-related thread, a question has planted itself in my brain, and I would be interested to hear the opinions of my fellow airgunners (especially those who have a deep understanding of powerplant mechanics and limitations). Namely, is it theoretically possible to create a viable large-game hunting rifle (meaning .45 or .50 cal, 800-1000 fps) using a spring or gas-ram powerplant?
Click to expand...

30 cal springer is as logical as putting as 4 cylinder engine in the M1 Abrams tank sir. It will drive it but not very far.
 
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Air powered guns have their place and are big fun as well as very useful within a realistic power range of up to 200 ft.lbs max. As you attempt to move into powder burner range things just get silly. You get a gun that will make 1 or 2 shots per fill and it wont even come close to matching the hotter pistol rounds. We are limited to a max of around 4000 psi unless you want to go to a nitrogen setup. Even the weakest pistol rounds run around 10,000 psi with high powered rifles run 60,000 psi. If you want to shoot a gun with powder burner power just shoot a powder burner.
 
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"sharroff"We have a 500 fpe .45 PCP (Texan) that puts out twice the energy of a 45 ACP handgun shooting match ammo. It's so long it doesn't fit into some gun cabinets and loud enough it sounds like a real rifle going off (which it is). Why take that and force a spring into the equation?


Click to expand...
From the original post: 
Namely, is it theoretically possible to create a viable large-game hunting rifle (meaning .45 or .50 cal, 800-1000 fps) using a spring or gas-ram powerplant? Logistical considerations aside (cost, weight, insane cocking force and murderous recoil), is it possible to produce sufficient muzzle velocity, and how might it be done? If we can come up with a decent answer (and I can come up with the cash), this may turn into a custom-built abomination.
Click to expand...

Again, this thread is about making a springer in a similar class that can be shoulder fired. 

Let's design this thing! Do we want to use a caliber .45 with a 192 grain pellet (1.4 times the weight of a lead round ball which is about proportional to a 11.5 grain .177 or a 22.4 grain .22), or the caliber .50 with a 263 grain pellet? 

Next, we need a barrel length. What is the shortest barrel (in terms of caliber) springer that meets the desired 850 ft/s or so with these weight of pellets? We can use this as a baseline. That is, take the barrel length in inches and divide by the caliber. Use that and multiply by either .45 or .50 to determine the length of the barrel for this big springer. 

Taking our sample smaller caliber springer, we need to determine the volume of the compression chamber of the big gun (again in terms of barrel volume). We will need to choose a compression chamber diameter as well.

Then, we need to figure out how much air pressure the original spring can generate, and/or its energy (average force time the travel distance F x d), and scale this up to our piston diameter. I think that a gas spring of some sort would be easier to build since we could vary the pressure in it to get the force/energy required. 

Finally, we need to consider how to put this monster into a shoulder fire-able stock. A trigger release mechanism that does not require a 40 pound trigger pull, yet is safe. And a means to cock the thing fairly easily. 
 
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I would say .45 for caliber (large enough for deer in most localities, while saving .05 or so of an inch in bore diameter). I have heard that the maximum barrel length for most spring-type rifles to maintain accuracy is 24 inches with the ideal being 12; I would err to 18, so as to provide more leverage for cocking while maintaining a reasonable bore volume. Beyond 24 inches, the compressed air behind the slug loses compression and the projectile begins to drag in the barrel.
A thought occurs to me; perhaps, in order to calculate the required dimensions of the compression piston, we may need some input from the big-bore PCP cognoscenti. Namely, in large-bore air rifles (the Texan being an excellent example) how much actual air is displaced during a full-power firing cycle? How much volume at what pressure?
Most figures list the fill pressure at 3000 PSI, but does that translate to it releasing a charge of air at 3000 PSI for one shot? I suppose the volume of air needed could be calculated, as I_Like_Irons suggested, by the internal volume of the barrel. The calculation of this (18 x 0.454) gives us an internal barrel volume of roughly 8.2 square inches. Therefore, a cylinder diameter needed to compress that volume to a pressure of 3000 psi can be reverse-calculated, assuming a standard 21" piston stroke length. Said diameter would need to be... uhhh... I'm not good with geometric calculations. Tag out?
 
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You will need a proportionally longer barrel in order to achieve the velocities. That is if a caliber .22 barrel that is 18" long is needed, then for a caliber .44 it needs to be twice as long---slightly longer for the .45. If , for example, the .22 can get by with a barrel of 12" then our big bore .45 will have a 24.5" barrel.

Spring guns by their nature have different and improved efficiencies over a PCP, in that not nearly as much heat is lost in the cycle. The PCP starts with ambient temperature high pressure air that cools upon expanding as it is released down the bore. The spring gun, on the other hand starts with ambient temperature and pressure air that is rapidly compressed, thus heated. As it propels the pellet the air cools back to ambient, minus a little bit heat that transfers to the barrel. This is a more efficient system. 

Just as another example of scaling, let us say that our sample .22 has a 1" diameter piston, and a stroke length of 1/2". (These are numbers grabbed out of the air and probably do not reflect a real springer). To maintain the proportion, our .45 will need a piston of 2.045" diameter and a stroke length of 1.022" 

For the spring, however, if the sample .22 has an average force of say 100 pounds over the 1/2" stroke, our .45 will need a bit more than 4 times that. The spring force will have to go up as the square since our piston area goes up by this amount. 

If we are making a break barrel, the actual cocking force will be just about double. Our barrel is twice as long which gives you more leverage, but the spring force is about 4 times greater. 

As I pointed out earlier, this thing may take on the proportions of a punt gun. Although a gun with a 30" barrel is not all that unwieldy. We just have to tidy up the spring compression end, by perhaps having half of it surround the barrel. 
 
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A light gas gun is basically a giant springer in which the piston is driven by a pyrotechnic charge and the gas in the chamber is hydrogen or helium. I don't understand all the physics, but lighter gases are able to transfer more energy to the projectile. Some people have reported small but measurable increases in muzzle energy after filling their PCPs with helium. https://en.wikipedia.org/wiki/Light-gas_gun

One thing to keep in mind if anyone is actually thinking about doing this: hunting regulations for big game may specifically require a PCP in order to allow quick follow-up shots for humane kills and hunter safety. Arizona is like that.
 
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"I_Like_Irons"
"sharroff"We have a 500 fpe .45 PCP (Texan) that puts out twice the energy of a 45 ACP handgun shooting match ammo. It's so long it doesn't fit into some gun cabinets and loud enough it sounds like a real rifle going off (which it is). Why take that and force a spring into the equation?


Click to expand...
From the original post: 
Namely, is it theoretically possible to create a viable large-game hunting rifle (meaning .45 or .50 cal, 800-1000 fps) using a spring or gas-ram powerplant? Logistical considerations aside (cost, weight, insane cocking force and murderous recoil), is it possible to produce sufficient muzzle velocity, and how might it be done? If we can come up with a decent answer (and I can come up with the cash), this may turn into a custom-built abomination.
Click to expand...

Again, this thread is about making a springer in a similar class that can be shoulder fired. 

Let's design this thing! Do we want to use a caliber .45 with a 192 grain pellet (1.4 times the weight of a lead round ball which is about proportional to a 11.5 grain .177 or a 22.4 grain .22), or the caliber .50 with a 263 grain pellet? 

Next, we need a barrel length. What is the shortest barrel (in terms of caliber) springer that meets the desired 850 ft/s or so with these weight of pellets? We can use this as a baseline. That is, take the barrel length in inches and divide by the caliber. Use that and multiply by either .45 or .50 to determine the length of the barrel for this big springer. 

Taking our sample smaller caliber springer, we need to determine the volume of the compression chamber of the big gun (again in terms of barrel volume). We will need to choose a compression chamber diameter as well.

Then, we need to figure out how much air pressure the original spring can generate, and/or its energy (average force time the travel distance F x d), and scale this up to our piston diameter. I think that a gas spring of some sort would be easier to build since we could vary the pressure in it to get the force/energy required. 

Finally, we need to consider how to put this monster into a shoulder fire-able stock. A trigger release mechanism that does not require a 40 pound trigger pull, yet is safe. And a means to cock the thing fairly easily. 


Ok, design the monster. Pick the springer of your choice. Make note of the FPE it produces and the weight of the gun less the sock and hit that number with the appropriate multiplier for a rough idea. Lets say you have a fairly stout springer putting out 20 ft lbs. and the mechanism weighs 8 pounds. 500/20x8 lbs. = 200 lbs. Your monster weighs 200 pounds and would have double+++ that for the cocking force. With the use of titanium you might be able to get it to 130 or so pounds. And buddy boy think about the reverse recoil and stress on the mechanism, not to mention the shooter.

Air guns are great fun and have their place in the shooting sports. If you just gotta push it to the max go with a 5500 psi, one shot per fill, nitrogen pcp gun. Make the bore large enough as in an inch or greater and use sabot rounds. What you end up doing is making a monster that just might be able to duplicate a $300 dollar center fire for $30,000+. As for me, I will just grab my trusty old Winchester M70 in 30-06 and know I have a sensible tool for the job at hand.
Click to expand...
 
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