Why not a fuel-air rifle?

Kurt: Also on the issue of locking and unlocking the piston. I'm afraid I'm not much good at mechanical design but my impression is that a number of semi auto rifles have to lock when fired (an AR15 for example) and unlock when the impulse from the gas tube arrives at the bolt carrier. I'm not up on the AR's design but I think that somehow that impulse is used to rotate the bolt out of the locked condition and then push the bolt/bolt-carrier assembly back against a large spring. If so a variation of the AR's mechanism should work in this instance.

Anyway if I ever decide to try this, first I'd want to see if I could get a single shot rifle to work. Semi auto would be a much more complex operation.

=rod=
 
Rod,

I love this idea; but it's starting to sound too easy! Where are the engineers in the crowd to point out what might be missing?

Here are a couple of thoughts that occurred to me on the drive home:

150 ft lbs is, I believe, correct pressure in most engines; so the 1200 lbs of compression is more than adequate. But what about the *volume* of gas necessary to operate the mechanism? Isn't this an issue as well?

1200 lbs of water pressure, for example, is considerable; but you still need a certain volume of water to turn a wheel. I was never good in science; but isn't it Weight X Distance = Force? Wouldn't we need a certain volume of gas to generate sufficient force?

Reading the gentleman's fascinating post from the other forum, made me wonder about the rate of speed at which the gas would need to be produced. I relate that to fast or slow burning powders. Would diesel fuel burn quickly enough? Or would something as volatile as gasoline, acetone, or isopar, be necessary?

As for the locking mechanism, there are many. I don't pretend to understand them thoroughly; but there are the various locking lug designs, blowback designs, rotating barrels, etc. No problem here! This we can get solved!! ;-)

Keep working on it! Pretty soon you'll be ready to take the "RodRifle" public!

Kurt
 
About 25 years ago the US Army conducted tests with small arms ammo using liquid propellants. They never found one which would equal the standard propellant, nitrocellulose. Which, BTW, is very cheap.

As far as fuel air guns go, check back about 3 or 4 years in Scientific American. They had an article about a 'gun', actually an assembly of separate structures, including several tons of weight on a railroad car to absorb recoil (some of it anyway; it recoiled in three directions). It used hydrogen and air as a propellant, and was used for propelling small lifting bodies (aerodynamic shapes) for the U S Govt. I believe they reached Mach 7 or 8. Walt
 
I'VE GOT IT.

OK, all we need is a SMALL two-cylinder gas motor. Right? Little 100cc pair of 50cc cylinders, I had a two-stroke 100cc '65 Yamaha laid out like that, the motor (sans tranny) would have weighed far less than an M60.

Pull one spark plug. On that same cylinder, plug the exhaust port and pull the carb. Run a major-heavy-duty rubber hose off the spark plug hole...and connect it to the barrel. Right in front of that you need a mechanism that'll pull a hollow bolt back, throw a round in the chamber and throw the bolt forward...drive that mechanism off the crank.

We now have a high powered full auto single barrel gun with no actual combustion in the barrel and therefore, spin the sucker up to 10,000RPM and get an ungodly rate of fire. Use round lead balls for easy feeding. Rate of fire is adjustable via the throttle on the cylinder that's still firing and running the SOB.

Ohhhhhh MAN ya. I *think* 50cc of power would be adequate, if not use a 200cc twin. Whatever.

A couple of points here: two-cylinder motors WILL run on one cylinder. I once had to limp 40 miles out of a wilderness area on one cylinder of a twin 650cc Yamaha; 325cc worth of power let me cruise at 45mhp. I could have done better by pulling the plug and exhaust on the dead side, as it was I was fighting compression on that side but I was counting on a quick fix back in town, which happened.

Cool, no?

Jim March
 
Jim; I want you to go back on your medicine. Now. You need it. Dr. Walt

PS; whatever you do, don't reread Heinlein's 'The Moon is a Harsh Mistress.' I don't want you reminded of the linear accelerators the Lunar Colonists used against the Earth fleet, shooting iron spheres cast in zero g.
Trust me, it would be too much stimulus for you now. ;) Walt
 
Walt, shaddup, I'm having FUN here :D.

Lesse. Assuming a two-stroke you could get 10,000 rounds per minute :D. If we go four-stroke for reliability you could gear the pellet/boltaction at 2:1 off the crank, because otherwise every other piston rise would be "underpowered" because the side that's still got a working spark/fuel system isn't kicking off. So you go to 5,000 rounds per minute on a 10,000 ROTATIONS per minute motor, and every other air pulse is *not* driving a round and therefore cools the barrel.

HELL ya. And it's all basically off-the-shelf tech. The bolt action that feeds the pellets in needs to be on oiled bearings 'cuz it's gonna be movin' like a bat outta hell. You shouldn't have enough heat to ignite high-tech synthetic oils, and you'll want to allow a small amount to flow down the barrel anyway, lubricating and cooling the barrel.

Only weird thing is your pellet velocity *AND* rate of fire will climb as you give it gas. You should be able to rev the motor prior to "dropping the clutch" which gets the bolt flying back and forth and the pellets spewing like you just bought shares in a bearing factory.

Ohhhh HELL YES what an evil critter!

:D :D :D

Hey guys: anybody know if the BATF is lurking?

Jim March
 
Jim: Yeah! For military applications you could attach a chain saw blade for close encounters instead of a bayonet. You could build a log breastworks while waiting for the buggers to show up.

If you got mud and water in the trenches hey, hook up a pump, it the swiss army knife of assault weapons.

=rod=
 
Ok, If we go with the diesel principal, air compressed at a ratio of about 16:1 will heat to approxamatly 2000 degrees. At this point a mechanically linked fuel injector could inject a small amount of diesel fuel resulting in a controlled burn. (BTW: this is exactly how diesel engines work) This is where it gets tricky, here we need an exhaust valve of some sort to release this energy through the barrel to fire the gun. Basicly, the firing chamber would be seperate from the barrel and release its energy at the right time. So a repeater would be very possible since the bullet wouldn't have to sit directly on the charge. Further, if we rigged everything through simple mechanical linkages, we wouldn't need electricity, pumps or any external components at all. This thing might not only work, but could even be carryed and fired by one man.
 
Grayfox: I have been talking to another guy who is familiar with I.C. engines and he takes the same tack you do, go diesel. But when he did the calculations he finds that there isn't enough energy with a starting volume about equivalent to a 50 bmg case to get more than nominal velocities out of a .22 cal 40 grain bullet(maybe 700 fps). Now a 50 bmg case sounds big to someone familiar with rifles but in spring piston airgun terms that's not a lot of volume. A typical SP airgun chamber is 1" in diameter and has a stroke of about 3.25" quite a bit more volume than a 50 bmg I'd imagine. Anyway this guy says that precompressing the charge is what the tank gun must have done. Also wouldn't you have to have a pretty powerful pump to inject fuel into a cylinder pressurized that highly (16:1)?
 
Rod,
I was told some diesel engines in Germany were running 20:1 ratios and lasting for years. (circa 1975)

Jim,
Using a rotating, multi-barrel setup. If exhausting contaminants or barrel overheating becomes a problem, why not blow air thru each barrel just after it passes the firing position. Use one or more positions (as the barrel rotates) to get the amount of air flow you need to do the job.

If you're using an IC engine of some kind, you could add a cylinder(s) for extra power (if needed) to generate adequate air pressure.

If all this gets too big, heck, mount it on a jeep (oops.. er, that is) Humvee, a flat-bed truck (for civilian insurrections), or whatever.

Heck, mount two or three of 'em and have an Earth-bound Puff! (It only takes a minute.)

Hmm, a lightly-armored flat-bed truck could have two or even three across the front of the bed and two more on each side. Six or seven of these buggers could be pretty persuasive under proper conditions.

Kodiac,
Paint this dude BLACK and it would be the ULTIMATE TACTICAL support vehicle. :) :)
 
You could use a triple-cylinder engine and turn one into the "dead drive piston", or a four-banger, whatever. You'd probably do better with a bigger twin though.

In my design there's NO combustion going on in the cylinder that's driving the projectiles. It's being cranked by the cylinder(s?) that are still "live"...so you don't have to worry about combustion gasses/residues in the firing mechanism.

Even if you go diesel, I think this is still the answer, use one pr more pistons to "drive" the non-firing air compressor piston.

By the time you hit 10,000RPM you'll have enough air velocity to REALLY work it.

Jim March
 
Rod,
Actually hydraulic pressure is much easier to produce than air pressure, so the fuel injection isn't a problem. While I didn't mention it, I was concerned about air volume being too low. Ok, we make it bigger. I like the rotating multi-barrels idea. Picture this, a large single pressure chamber with rotating multiple barrels. Bullets feed into the open breach end of each barrel during rotation and are fired as they came into line with the pressure chamber. A fuel-air gattlin gun! Heck, we could mount it on Dennis' " Ultimate Tactical" vehicle and really rock!

I just had a strange thought, if there's a BATF agent somewhere reading this he must be about to have a heart attack! Or maybe ROTFLHAO :)
 
I have a “Potato Gun” made from some PVC pipe. You jam a potato down the muzzle end; unscrew the cap on the back end and spray in a half second spray of hair spray; quickly screw on the cap and pull the trigger(which is a standard gas barbecue igniter screwed into a hole you drill and tap in the area of the chamber). Let me tell ya if you get your mixture right you get some “HOIST” from this baby. It will throw a potato 300yds or more. Not a toy … well maybe a toy to be used under supervision.

Seriously though Rod … I think the fuel-air has merit particularly with large weapons such as naval guns. It would be much better then silk bags of black powered.


[This message has been edited by Scott Evans (edited February 26, 1999).]
 
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