Recoilless Rifle

[BlackTallon]

I am dreaming of a recoilless rifle, but not much is posted on this topic. I have the book floating around "Improvised recoilless rifle" or whatever it was called, but I am thinking of something a little more advanced that the "cookie" launcher design. The thought of using a fairly massive weight to cover two large vent holes seems to have merit. When the propellant was ignited, the projectile would begin moving, as would the more massive counter weight. Being more massive, it should have to travel a shorter distance to counter act the recoil forces from the projectile. When the counter weight reached the full extent of it's travel, the gas could be vented through holes like a large mussel break of sorts in the rear of the rifle. This would reduce the pressure in the barrel and should keep it recoilless. Then the counter weight could be returned to it's forward position with the aid of a large spring. Any input guys?

[nbk2000]

Asides from posting a topic for your very fist post, spelling "Black Talon" (the bullet) wrong, and bringing up a topic that HAS been talked about endlessly, I'd also like to point out the following fact.

"An object in motion will stay in motion till external forces stop it."

In other words, your massive counterweight will continue to move after it passes the vent hole till it either flyes out the back (recoilless) or hits the back of your launcher (recoil).

For true recoilless without a water/cookie/etc counterweight, you need 5 times the projectiles weight in propellant powder (smokeless) plus a rupture disk to build up the combustion to critical velocity.

1 part propels the warhead, one part of combustion gases acts as counterweight, and the other three provides enough "ommph" to get it all moving.

[BlackTallon]

NBK,
Pardon the typo in my name and my posting so soon. I have a question however. Not to sound smart but, If this has been talked about so much, why can't I find it? I have conducted a proper search. The only thing I came up with was something talking about that new 20mm/5.56 over and under combo they are making, (I don't recall what they call it.), and a thread on Bazooka vs. RPG. I can find nothing dealing with an actual recoilless rifle. If there is something on here, please direct me to it.
""An object in motion will stay in motion till external forces stop it."
In other words, your massive counterweight will continue to move after it passes the vent hole till it either flyes out the back (recoilless) or hits the back of your launcher (recoil)."

I know there would be a little recoil, but how substantial would it really be? After the counter weight passed the vents, the pressure in the barrel would be reduced to nothing. If timing and the spring pressure were right, most of the "recoil" caused by the weight hitting the back of the rifle could be absorbed. Anyway, if you have ever seen a 75 or 105 mm recoilless being fired, there is actually a bit of recoil. You could also use the vent gasses in my idea for a mild venture effect which would further tame any recoil that would be present.

[Anthony]

Venting the barrel/chamber gas does nothing to reduce recoil (unless the jet effect of the escaping gas is used to push the weapon in the opposiion direction to which it is recoiling - like a muzzle brake). All it will do is stop thge counter weight from further accelerating. All it would do is store the recoil energy in the moving counter wight, which if you don't want it flying off, must be absorbed. This puts you back to square one. A large spring would help but the counter weight pushing the spring would impart recoil on the gun.

Maybe fit the action on rails with springs or better, dampers and use a good muzzle brake.

It would help if you were more specific in what this weapon must be like. You mention "rifle" which could imply a 50cal weapon, or do you mean something like a 110mm for firing anti-tank rounds?

[Arkangel]

The system you are describing is not dissimilar to a blowback type weapon, where the light projectile is accelerated very rapidly at the same time as the (equal and opposite) force is being applied to the relatively heavy breech block. In practice the bullet has left the barrel pretty much before the breech block has made any significant movement. When it does begin to move, it does so with some force, and is then pushed forwards again by the mainspring of the gun. That mainspring then exerts a force on the weapon body, which exerts a force on you. If you've ever fired a blowback smg you will be in no doubt that the recoil is there, and is enough to push you and your aim all over the place if you're firing a burst.

Scale it up (if that's what you mean) and you will have more recoil than you want to deal with. As NBK says, the only way you truly get a recoiless weapon is when an equal part of the charge is directed to keeping the weapon stationary.

[BlackTallon]

I think I will use this time to clarify myself a bit. What I am thinking here is a big bore, in the three inch category with a one or two pound projectile. Not a standard rifle by any means. Something much like the military 75 mm recoilless rifles. All I really want to do is get rid of the plastic blow away plug and the complicated casing and venture system. If you have ever seen a recoilless round, the casing is full of holes and there is a plastic cup like device that builds the pressure up as NBK mentioned. When the plastic thing ruptures, the gasses flow out the holes in the case and through the venture. The venture accelerate the gases to the point that the forward force from the venture equal the rearward force from the gases pushing on the projectile. This renders the weapon "recoilless." (Although there is a bit) I am thinking of a mussel loading weapon. I may be wrong, but it seems to me, that if you had a 1 pound projectile, and a 2 pound projectile with propellant between them and it were ignited, the 2 pound projectile would move half the distance of the one pound projectile in a given time. If that were true, a 5 pound projectile would move 1/5 the distance of the one pound projectile and so on. If barrel length, projectile weight, and counter weight were calculated properly, you could theoretically get to the point where the projectile would leave the barrel and the counter weight would only move 2 inches or so. Now yes, the weight would smack the back of the action, but the velocity should be fairly low, so not much recoil would be generated in the first place. I still want to vent the gases through venture like a mussel break, I just don't want them to be too complicated. That is why I was thinking about the vent holes. I envisioned a 90 degree bend, and then some cones to deflect the vented gases to the rear.

Also, springs can be used to absorb quite a bit of recoil. If you have any experience with Barrett 50's there is a drastic difference in the recoil of the A1 and the 95. They are basically the same weapon. The break is the same and everything. The semiautomatic A1's recoil is around that of a 12 gage shotgun. The 95 kicks the shit out of you. It is more like a 300 Winchester magnum from my experience. The difference is only that one is a blowback weapon and the other is bolt action.

Now, as for smg's there is recoil, but the bolt weight has an effect on that too. They use fairly light bolts to keep the ciclic rate up. All that chattering back and forth jars you around a lot, and you don't have much control. In an open bolt smg, when the bolt smacks forward, you are pulled down and left. When the bullet fires, you are pushed back and right. When the bolt becomes more dense, the ciclic rate goes down, and controllability increases. Shoot a sten. They have a heavy bolt, and I don't think there is as much recoil as some smg's with lighter, faster moving bolts.

http://www.roberts.ezpublishing.com/rarmory/rrifle.jpg

[Anthony]

Assumbing you have a 2pound projectile with a range of 500m, your counter weight, in order to come to rest in say 50cm would have to weigh around 2000 pounds. I doubt it's that linear due to the different ballistic efficiencies of different size/shape projectiles.

Also your counterwight would have to open to the air as air resistance robs most of a projectiles energy. If it wasn't, you'd have to stop it by friction alone which would work.

Another great thing is that slow heavy projectiles (counter wight) have better energy retention than light, fast ones (projectile). So your counter wight would decelerate at a much slower rate than your projectile (and it's got to stop in, what 2ft). This is because as velocity doubles, air resistance quadruples.

[Arkangel]

I'm not saying that the recoil on an smg is uncontrollable, or comparable with a 12 guage, especially .50 cal. Firing a burst from the sterling smg (L2A3 - as used by all the imperial stormtroopers in Star Wars if you look closely) you can pretty much keep most of the rounds on a man size target if you practice. It is, however significant and it sounds exactly the same principle as you describe for your "recoiless" weapon, which would at best be a reduced recoil weapon.

The physics are simple, newton's 3rd law - equal and opposite reactions. You fire a projectile, that projectile is exerting an equal and opposite force on whatever is pushing it, either the gases pushing it from the front of an open ended tube with equal force going out the back of the tube, OR the gas/barrel system that constitutes the gun, however it is operated.

Muzzle brakes are only marginally effective since they only work for the fraction of a second when the projectile is passing through the brake, and by then, most of the recoil forces have been passed to the barrel.

I have to ask questions about what you actually want to achieve. Does it have to be portable/reloadable etc. If portability is important, your counterweight system is not going to work. If it doesn't have to be combat reloable, then you could probably design something along the lines of a normal military weapon, just test it with different propellant loads until you get it right. Of course, if you want to fire it personally from an enclosed space you're fucked. Tell you what, why don't you just make a normal barrel, then wedge it up against the corner of a house or a big rock or something, that way there is recoil, but you don't feel it......

There was an interesting programme a while back called scrapheap challenge, where 2 teams make something from stuff they find in a junkyard. One time they made a cannon. The best one was made from a hydraulic ram body and was firing a steel ball about 3" diameter. They first used bp, then a commercial propellan, but in both cases, the recoil knocked the shit out of the carriages they'd built. Do let us know how you get on!

[blacktalon]

Anthony,
I mente inside the barrel. Once the projectile leaves the barrel, there is no more gas pushing on the projectile or on the counterweight. (propellant gas anyway)

I once saw a recoilless rifle with a similar principal to the one I am thinking of here, so it can be done guys. I think It may have been Swedish. In their design, there was a counterweight that weighed the same as the projectile, but the weight had large pop out fins on it. When it came out of the tube, it expanded, kind of like a backwards umbrella. The counterweight did however, stay with the weapon. The thing was, their design was a one shot weapon kind of like the American LAW, only without the rocket engine. I am thinking field reloadable and man portable. If you don't believe me, look in the big book of modern weapons (I think that is what it is called) It has a white cover with blue lettering. I think there is a 66 mm flack cannon on the front of something like that. It shows a cross section and everything. Maybe next time I am out I will buy the book and scan it for you. That would probably help.

Arkangel,
I know a regular old blowback system is by no means recoilless. The opposing force would be the vented gases. My idea would be more effective as well because you would have the vent holes uncovered while the projectile was still in the barrel, there by using all available gas. Also, venture increase the velocity of the gases unlike a mussel break. That should give you a little more oomph.

[Arkangel]

Oooooh, nbk got to you then. Personally I thought Black Tallon was ok, kind of sinsister/dyslexic combined.

Anyway, the 66mm you describe certainly sounds intriguing, do please post something if you can.

I can see what you're saying about having the gases vented further down the barrel and a VENTURI would help increase gas velocity (at the expense of higher barrel pressures - more force on projectile and recoiling weapon), but really this is a variation on the traditional systems which work well in any number of configurations, you simply have a single venturi at the rear of the barrel.

You seem insistent on the counterweight and I'm curious why, do you need to fire it from a confined space or something? If so, over what range? In WW2, British forces had something called the PIAT, a Projector, Infantry, Anti-Tank. This was realoadable weapon that looked like a weird bazooka, the difference being that the projectile was fired by a spring.

<a href="http://ourworld.compuserve.com/homepages/AdamWilliams2/piat.htm" target="_blank">http://ourworld.compuserve.com/homepages/AdamWilliams2/piat.htm</a>

Check this out, but as you can see, it was hardly recoilless. Depending what you want though, it could give you a solution

[Anthony]

That's a spring/piston airgun taken up a serious level! :)

That umbrealla counter weight doodad would have had to dissapate it's energy by friction alone. Not a problem for single shot but practically impossible to make reloadable, simply because of the force required to force the counterweight back into ready-to-fire position. Wear and tear would also severaly limit the number of shots that could be fired.

What would happen is your counter wight system failed to operate? Would the recoil break your back?

What's wrong with having your launcher use a water counter weight that would be ejected from the rear of the launcher? It would be a lot simpler to make and easily reloaded (have the water built into the round).

What sort of machinery do you build this weapon?

Arkangel, IIRC the homemade cannons had a bore of around 1.5" which shows that the recoil was even more potent.

In regards to the effectiveness of muzzle brakes, I was under the impression that due to the velocity of firearm rifle rounds, the projectile left the barrel before the recoil affected the shooter?

[Arkangel]

Yeah, it's a bit like the old long range crossbows, where they had a screw to wind the bolt back. I'm sure something neat could be made quite simply though.

A water counterweight is a much safer idea, what would be wrong with a balloon of water the same size as the projectile? Particularly if you are in a confined space.

So, you saw the show Anthony, lucky BASTARDS is all I can say, I laughed my arse off when the barrel came off the one built by those those clueless Army wankers. :D I mean really, SSSB ammunition! (string stabilised, stuck in the barrel)

Regarding MUSSEL BREAKS (It's MUZZLE, not MUSSEL [shellfish] NBK2000) (sorry Blacktalon, but you'll get there in the end), ALL the recoil energy has been passed to the weapon body before they take effect, but bear in mind that by the time it reaches the muzzle brake, it is at it's maximum velocity and the effect lasts for microseconds. Even if all the effluvium were directed rearwards at that moment (and that might sting your eyes), it would not make that much difference. They work, but not so much that you couldn't do without them.

[ January 08, 2002: Message edited by: nbk2000 ]

YIKES :eek: - I don't know why you corrected my post nbk, as I'd have thought you would have spotted it first in the 3 or 4 posts of B/T's that I was referring to. Maybe if you're from the US, sarcasm is a bit baffling, but then having seen enough of your infamous work before, I don't think so. Whatever, thanks for your caring touch. ;)

[ January 08, 2002: Message edited by: Arkangel ]</p>

[Yikes]

The weapon black talon is talking about is the German Armbrust short range anti-armour weapon.

This is a very interesting weapon as it has NO firing signature: no flash, no smoke, quieter than a pistolshot, yet firing a "missile" some 300 metres!

How is this done:
A propellant charge is sealed in a strong tube between two movable pistons. In front of the front piston is the projectile (AT-warhead), behind the back piston is a folded umbrella-shaped counterweight.
On firing, the pistons move to the ends of the tube, propelling the projectile forward and the countermass backward. The pistons actually stop at the ends of the tube, keeping all combustion gases in the tube. Projectile flies further to target, counterweight leaves the tube at the rear. On leaving the tube, the counterweight folds open, drastically increasing it's drag. There is no backblast, so you can fire the weapon from within a bunker, livingroom etc. (Try THAT with an M72 LAW!), needing a minimum distance from walls of only 0.8 m.

[blacktalon]

Yes, I do like the counterweight idea because it would be useful in confined spaces. Most recoilless rifles have a danger area behind them of 30m. You don't even think of firing them inside. You would be very dead. I am thinking of something useful out to 500m or so.
I have seen the PIAT. The only problem with that thing is it is a pain in the ass. I have heard it was all a soldier could do to cock the darn spring (the link said something like that too). I want to design something that can be transported, and served by one person.
I don't suppose there is anything wrong with a water counterweight. The only thing is that it would add to the weight of the shells, further limiting it's usefulness to a single person. The counterweight would add to the weapon weight, but that would be it. Water would add 2 pounds to every shell you wanted to lug around.
Yikes,
That's the one! Thanks a lot! What do you think? Could it be made reloadable? What if you had a propellant holder that was not a part of the projectile. Then you could refill the propellant reservoir, push the plungers back in, and load a new projectile.

[blacktalon]

http://www.jed.simonides.org/support/law/armbrust_series/armbrust-title.jpg


<a href="http://www.jed.simonides.org/support/law/armbrust_series/armbrust-series.html" target="_blank">Arm-burst</a>

[blacktalon]

http://www.jed.simonides.org/support/law/armbrust_series/armbrust/armbrust_005.jpg

here we go now. go to this web site.

<a href="http://www.jed.simonides.org/support/law/armbrust_series/armbrust/armbrust-archive.html" target="_blank">Arm-burst</a>

[BoB-]

Your kind've getting carried away, venturi nozzles would kick ass, but for the hobbiest theyre not really practical.

The exact weight of the coins your country uses shouldnt be that hard to find, a stack of coins wrapped smoothly in aluminum foil could have there combined weight written on the side, the muzzle blast of the weapon would rip apart the foil dispersing the coins out the back of the weapon where they would lose velocity quickly.

Pill and film bottles full of sand or shot also come to mind.

Also, have you considered diameter? since recoil isnt an option 3/4" or 1" projectiles could be used, good luck finding "safe" sch. 80 pipe though.

[JoeJablomy]

The idea here sounds kind of like something I think I saw on the Army Science Conference website, or maybe IBS. It's called a rarefaction wave gun (RAVEN), the basic principle being that if you vent the propellant gasses at the breech when the projectile is already 1/4 to 1/3 the way down the barrel, the pressure drop does not reach the projectile until it's already left the barrel. I'm sure this is partly because the greatest acceleration takes place in the first few inches of barrel and the round is probably already going supersonic (probably not to the really-high-pressure propellant gasses, though) after the first foot or so.
It's pretty much assumed here that by "venting the propellant gasses" we mean putting them through a DE LAVAL or C/D (NOT VENTURI, those are subsonic and totally unsuitable for rocket propulsion) nozzle, which in this case would probably be nothing but an expansion cone.
The army test device consisted of a 25x137 barrel (25x137 is a NATO round, for those of you who might think this meant the barrel dimensions) and a spring loaded breech block and used ammunition scored at the base to cause head seperation. The 'receiver' the barrel was screwed into had a divergent conical section that the block fit into. When fired, the block recoiled at a rate determined by the mass and spring tension, the case head tore off, the gasses vented out the divergent nozzle formed by the block and the breech itself, and the remainder of the casing Usually got ejected by residual pressure. Recoil reduction was 40-60%, I think.

The heavy breech block moves less to the rear than the projectile moves forward during a given time, and also with less energy, in proportion to their mass ratio, true. The problem is that any gun does the same, so if your breechblock absorbs recoil pressure for 1/3 of the time the barrel is pressurized, it has 1/3 of the recoil <I>impulse</I> a conventional gun would have anyway. It has much less energy than the projectile, but to move 2" compared to a 60" barrel, it would have to weigh 30 lbs (1 lb projectile) for your hypothetical 30mm gun, which is itself a bit too heavy to be portable. Actually, to give you an idea of what's going on here, the projectile will probably leave the gun in 1.5-2ms, which means your breechblock is travelling to the rear at 2"/.002s=1000i/s=83.33fps, which gives something like 3240ft-lbs energy.
This impulse will have to be transferred to the gun, which to reduce the energy to manageable amounts would have to be enormous. Of course, as I said, you might avoid 2/3 of this by venting, and if you make a really good nozzle, perhaps even an ejector of some kind, you might counteract even more. But it still wouldn't be very practical.

I guess there are two challenges that I in my crappy college apartment room can see to RAVEN design:
1. Valving. You want the ports fully closed for .0005s, then fully open within a basically impossible time frame, like within another .00005s. Or you could settle for partially open at .0003s and fully open at .0006s, although the beginning of the rarefaction wave would definitely hit the projectile and rob it of velocity. Either way, you'll have fun.
2. Nozzles. For this to work very well, you'll have to design a very good path from the breech ports to the air. As few sharp bends and corners as possible, I guess (not having too much education in fluid dynamics). Then you have to have your expansion nozzle, which accelerates the gas to the highest velocity you can get. This is equivalent to expanding it to atmospheric pressure, although how much expansion that is depends on the pressure of gasses going in, which varies, so you have to figure some compromise. Also, where along the length of the gun do the gasses come out? Is it a bolt action where the breech face, or, more importantly, the case mouth of the cartridge, where you will probably be harvesting the gas, is one or two feet from your shoulder? Or is it just a single shot bullpup? You could have a blast tube going over your shoulder (it's been done), but that might take several percent off your nozzle efficiency, which could be unacceptable. What I would do is make two nozzles, each with a large rectangular or ovoid opening to give two flat exhaust streams with air access between them and on the outsides, and this cluster would be right at the place where the gas is tapped off the barrel. The exhaust/air stream would be directed through a larger divergent duct that would carry the gas over the shooter's shoulder. This is an ejector nozzle, where the hot supersonic gas would combine with and expand/accelerate the air in the duct and some air that gets sucked in, thus increasing the propulsion mass and nozzle thrust. It's likely that some of the uncombusted propellant gasses would also combust.
There are a number of drawbacks to ejectors (weight, size) , and ways they're ineffecient(difficulty in mixing hot and cold gasses). The mass would just have to be dealt with; maybe it could be made from carbon/epoxy. The ineffeciency would largely be moot (assumption) because the nozzle would operate in pulses, and instead of trying to continually draw cold air into a hot stream, the hot gas simply runs into it and pushes it out the back. I saw an abstract by some russians about jet ejectors that can mix in either 50% or 150% air by disturbing or pulsing the streams; they hope this can compete with turbofans after further development. The twin flat nozzles are also intended to increase the surface/interaction area for the air that does get pulled in the front.

Overall, I'd test this as a 20mm before moving on to bigger stuff. At least in America, all the necessary materials for stuff in 20x102 is readily and even cheaply available, if you know where to look. It might be hard to adapt a vulcan barrel for this, though :(

One last thought on valving: if you use a gas piston to operate the valve, it doesn't have to have the same face area as the bore, which means it can be smaller, lighter, and faster than you might think at first.

[john_smith]

AFAIK the PIAT round wasn't thrown by a spring, it had a propellant charge in its hollow tailboom. Basically it was a just gun "in reverse", the barrel was attached to the projectile and the bullet/plug/piston/rod/whatever to the weapon. The rod also acted as firing pin, and was blown back and automatically cocked by the recoil. Do a search for "spigot mortars", there have been quite a lot of versions of them since the WWI, in all shapes and sizes. IMHO one would be a good choice for home manufacture since it allows for more freedom in designing the fins and the round in general. Of course, recoilless it ain't...

[chemofun]

Did the panzerfaust have a counter weight or did it use a lot of propellant with a rupture disk? I have seen conflicting reports.