Do recoilless rifles have recoil?

Depends on how you define 'recoil'

OK, I'll pull out my (rusty) minor in Physics: It depends upon how you define 'recoil'. If you assume the gases exiting out the rear are frictionless, and that the projectile is relatively frictionless exiting the front, then there is no energy imparted to the tube. Therefore in the macro case, there is no force (recoil) transmitted to the tube, and the weapon truly is recoilless.

Measurably and theoretically, if there is friction (or a blockage like the Afghan video noted above) from gases exiting the back (which there will be from both an absolute measurable and theoretical perspective), or friction of the projectile exiting the front of the tube, then energy is imparted to the tube and a force aka recoil will be generated. Clearly the forces involved are orders of magnitude less than a similar sized projectile from a non-recoilless weapon, but they will be there and will be measurable as there are no truly frictionless systems.

As such, from the micro perspective, there are forces (recoil) transmitted, albeit relatively nil by comparison, so the weapon is not perfectly 'recoilless'.

Kind of like the famous question 'what does the word IS mean'?
 
Friction

Probably something to that.

The projectiles for the M40 had pre-engraved copper or brass bands to take the rifling of the barrel. I always assumed that they were made that way in order to cut down on friction or to allow the round to get started down the bore easier. When loading it, you always had to spin the loaded round a little to get the engraved copper band to line up with the rifling.
 
OK, I'll buy that. But when you fire the weapon, you feel nothing. Sure, there may be some measurable amount of recoil due to friction but, it is not measurable to the human shoulder. I don't think anyone wanted to get that deep into it. For all practical purposes there is no recoil.
 
Surely there would be twist recoil from the reaction of the rifling making the bullet spin as it accelerates down the tube, or are the rearward facing gas jets angled to cancel that out also?
 
OK, that's something I can comment on.

During initial development it was discovered that the vents had to be angled in opposition to the rifling twist or the gun would torque. I seem to recall that while it wouldn't flip the gun, it did cause problems with the mount and the tripod, which weren't designed for that.

That's also part of the reason why the driving band is pre-engraved, it helps cut down on that torque and it also makes driving the projectile through the bore easier. It takes a lot of pressure to engrave the driving band, and apparently with an open system there simply wasn't enough pressure unless the band was pre-engraved.
 
I have only seen the old 106mm Jeep (M151) mounted recoilless rifle and I will confirm that the thing has more blast than anything else I've actually seen in person. To be honest, I've also seen a 105mm tank gun fired but I really can't remember which has more blast. And by blast, I mean from both ends of the recoilless rifle. In comparison, a 105mm howitizer has much less. But on the other hand, a modern 155mm howizer (a gun-howitizer, really), has rather more.

They were used extensively around the world in the 1950s and 1960s, some larger ones even, but guided missles have mostly replaced them in service.

The first editions of the "Small Arms of the World" by Smith and Smith included recoilless rifles.
 
Well, here is another thought. The M67 shoots a 90mm projectile. The .50 BMG shoots a .50 caliber or 13mm projectile and without the recoil management system not many of us would not be able to shoot it without possibly breaking bones. now multiply that by approximately 7 times. 13x7=91 and try to imagine putting that up to your shoulder and firing it if it weren't designed to be recoilless. Like I said, just a thought.
 
The M8c spotting rifle is .50 caliber (bore size) but uses a special round (smaller case than the .50 BMG) and is loaded to match the trajectory of the 106mm round.

The idea is to fire the spotting rifle at the target (it being a much less noticable blast to the enemy) until hits were obtained, then trip the main gun (106mm). One thing about a recoilless rifle, when fired, EVERYBODY in the area knows where you are! So you pinked them with the spotter, swatted them with the 106, and then boogied to keep their buddies from swatting you.

There is no felt recoil, the thrust of the gasses rearwards balances the recoil of the projectile launch. Net effect, zero felt recoil.

Lighter, shoulder fired RRs (like the US 90mm) do feel like they "lift" when fired, because the weight of the projectile (and powder charge) is removed when fired. Kind of like the way the Tommygun "climbs". The gun doesn't actually climb, recoil forces virtually balance the weight in full auto fire, but your mind (and arms) are still holding up a 13lb gun, so it gets lifted. people think its the gun, but really, its the operator.

A should fired RR will usually have some muzzle flip (so does a bazooka or RPG), due to the soldier holding it up, and it suddenly getting lighter when fired. Its not the weapon or recoil that causes it, its the shooter.
 
My group arms room kept a couple of the 106s on hand for training. I got to gun a round and AG another when we had a range day. You know you are crackin open a can of scunion when you tap that sucker off. As a demo, we set up a wooden pallet 10m behind and the backblast wiped it out. I have a couple of great pics I will have to dig up and post.

Few interesting tidbits I recall:
-as of 1995 it could still defeat any known tank armor
-it has a 6-7000m range and can also be used for indirect fire
-the flechette (or "beehive") round has a dial-the-range fuse on it. Estimate the range, set the fuse, and it busts loose with a few thousand flechettes at the appropriate range to saturate your target.
 
Here ya go...

These pics were taken at noon, probably Jan or Feb at Ft Bragg. The pic that shows the nice backblast evidently overwhelmed the light sensor on my camera.

In the well lit pic note the taped off backblast area.
 

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There's recoil. The recoil is what makes the projectile move. Just like a rocket. The exhaust gas/backblast is what generates the recoil and that recoil is applied to the projectile to balance the conservation of momentum equation.

In a conventional firearm, expanding gases push on the base of the bullet and on the breechface. The momentum of the bullet and escaping gases equals the momentum of the rifle as a result.

In a recoilless rifle, expanding gases rush out the back of the rifle and also push on the base of the projectile. The momentum of the gases/exhaust/backblast equals the momentum of the projectile.

The recoilless rifle doesn't get into the act because it's just an aiming tube. So there's very little felt recoil.
 
There's recoil. The recoil is what makes the projectile move.
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So I quess the inventor, the military, the physicist and all of us that have trained on them and fired them are just ignorant right? You know, they don't just hand you this extremely dangerous deadly weapon and say here you go, go fire this thing until you figure it out. They sit you in a class room and go over every aspect of the damn thing before they let you anywhere near the range. Again, what you are describing is reaction not recoil. Recoil is basically the rearward movement of the weapon in response to the projectile be fired out the front. Usually felt against the shooters shoulder, in the case of a vehicle or tripod mounted weapon, the recoil is transferred by the vehicle or the tripon to the ground. Since that doesn't occur with a recoilless rifle their is no (or at least not any appreciable amount of) recoil.
 
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Recoil is a reaction. That's pretty much the definition of recoil--it's an equal and opposite reaction to the action of firing.
So I quess the inventor, the military, the physicist and all of us that have trained on them are just ignorant right?
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No. The inventor was clearly talking about felt recoil, recoil applied to the gun and shooter and there is very little of that.

As TXAZ points out, the gun isn't really coupled into the system of the projectile and exhaust gases except by the friction of the gases and projectile on the tube which is small. So the recoil transmitted to the RIFLE and therefore to the shooter is small. From the shooter's standpoint the rifle doesn't recoil so it makes sense, from his perspective, to call it recoilless. The RIFLE is recoilless for all practical purposes.

But that doesn't mean there is no recoil. There is motion and any time you have motion, you have recoil as a consequence of conservation of momentum. In this case, the action is the rush of gases/exhaust/backblast out of the back of the rifle and the reaction/recoil is what forces the projectile out of the front of the rifle. It doesn't affect the rifle or the shooter to any significant extent but it's still there. It has to be--conservation of momentum demands it. And, in fact, in the case of the recoilless rifle, it's actually the recoil that makes it work.

Just as a rocket exhaust makes a rocket move as a consequence of the recoil generated by expelling the gases, the backblast of a recoilless rifle generates recoil and that recoil is actually what causes the projectile to move forward.
 
Again, you are confusing recoil with reaction. For it to be recoil, that reaction must react against the gun itself. Recoil is not the reaction, recoil is the rearward movement of the weapon caused by that reaction. In a recoilless rifle the reaction is just reacting on the atmosphere not on the weapon itself and therefore cannot be called recoil.
Just as a rocket exhaust makes a rocket move as a consequence of the recoil generated by expelling the gases
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Yes, exactly. The rocket is moving in the opposite direction of the blast, that is recoil. It is recoilling against the explosion. A recoilless rifle does not recoil against the explosion. Can you not see the difference.
 
...recoil is the rearward movement of the weapon caused by that reaction.
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That's a very narrow definition of recoil. Recoil is recoil whether it acts on a gun or on something else.

Rockets work via the principle of recoil but there isn't any gun at all involved. In fact, the "father of space" travel initially came up with the idea of a "recoil rocket" that could travel through space via the recoil generated by expelling gases--even though the gases weren't pushing against air.

http://www.buzzle.com/articles/how-do-rockets-work.html

"Just like the gun experiences a recoil when it fires a bullet, the rocket also experiences a recoil when it throws out the exhaust gases out of its tail. This recoil is so strong due to the very high velocity of exhaust gases, that it launches the rocket upwards!"​
In a recoilless rifle the reaction is just reacting on the atmosphere...
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It doesn't have to act on anything to work because it works on the principle of conservation of momentum--recoil. It would work in space, just as well as it does in an atmosphere.
A recoilless rifle does not recoil against the explosion.
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The RIFLE does not recoil. The RIFLE is recoilless. That doesn't mean that there's no recoil. The recoil is actually what makes the projectile move. The motion of the projectile is a consequence of recoil--the recoil generated by the exhaust gases/backblast. The recoil that doesn't act on the rifle to any significant extent.

In a regular rifle, the gases expand and push the bullet out of the muzzle. That motion generates recoil that acts on the breech.

In a recoilless rifle, the gases expand and rush out the rear of the rifle. That motion generates recoil that does not act on the rifle but does push the bullet forward out of the muzzle.

There's recoil in both systems, it's just that in the regular rifle system the recoil acts on the rifle via the breech and both the gases and the bullet exit the muzzle.

In the recoilless rifle the gases exit one way and the bullet exits the other way. The recoil generated by the exit of the gases does not act on the breech (there isn't one), it acts on the projectile and that's what actually makes the whole thing work.
 
The question was "does the recoilless rifle have recoil. It does not. The round coming from the recoilless rifle may have recoil but it does not react against the recoilless rifle itself therefore the rifle has no recoil. In your rocket ship scenario, the rocket is the projectile not the weapon that fired it.

Recoil: To spring back, as upon firing. To shrink back, as in fear or repugnance.
synonomous with: rebound, kickback, kick
 
Yes, there is recoil. I worked on the 106 and set them up for firing. The vent in the back is adjustable for wear and recoil.
 
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