Recoil and its effect on ballistics

[Bucksnort1]

A question I've had on my mind for many years is this.

If you fire a 30-06 rifle from your shoulder, you feel the effects of equal and opposite energy. Let's say you clamp the rifle in an un-movable stand of some sort. Neither the rifle nor the stand can move when the rifle is fired. How does the un-movable rifle affect ballistics?

Let me give you an example of an experiment I saw, a couple of years ago on television. Some men built a trebuchet (you know, one of those castle busting ancient devices that hurls boulders at castle walls). When the trebuchet is fired, it moves a few feet forward and backwards. They wanted to know if range would be affected by staking the unit so it couldn't move. They did this and found the machine had less range than when allowed to move freely. Yes, I know, there could have been slight differences in weight and shape of the projectile.

Comments?

 

[us920669]

I never attacked a castle so I don't know about trebuchets, but how tight you hold a rifle will definitely make a difference. If I'm shooting for hunting zero I'll hold the fore end with my hand, even if I still use the bags. Of course, if it's not a real hard kicker, you might just support the front with your fingertips when shooting in the field, so in that case resting the rifle on the bag would duplicate it.

 

[jmr40]

Yes, you will get a small increase in bullet velocity if the rifle is held firmly and not allowed to recoil. The difference is not huge, but real. There is another guy who hangs out here who has provided some evidence showing small differences between shooting prone vs offhand and slightly more speed from the prone position. I'd not be surprised if he comments on this in more detail.

 

[Bucksnort1]

As I said earlier, I have thought about this for a long time. Actually, since high school while in a physics class. Believe me, that was a long time ago.

Another reason I'm curious (curious, not concerned) about this is because I recently bought one of the Caldwell Lead Sleds (not the top of the line but the one that's about $100). It recommends using one 25 pound shot bag to eliminate the felt recoil of a 30-06 and to seriously reduce the felt recoil of magnum cartridges. In all the Lead Sleds, you hold down the front of the fore grip with Velcro then place the rifle butt in a rear padded slot.

I found two 14.3 pound (each) barbell weights which don't fit the Sled perfectly but will work ok. Theoretically, you could use the Sled to keep the rifle from moving.

 

[Mobuck]

Considering the difference in weight of the rifle vs. the bullet, I believe the bullet will have exited the barrel before the rifle will move a significant distance. Holding the rifle firmly in place isn't going to make an appreciable difference in velocity.

 

[James K]

Since the barrel is a closed unit until the bullet exits, no matter what the rifle as a whole does, I fail to see how allowing or stopping rifle movement could affect the bullet velocity. This sounds like the same kind of idea that if an airplane moving 2000 fps fires a bullet from a forward gun that has a 2000 fps velocity, the bullet will never exit the barrel.

Jim

 

[Tinbucket]

Reccoil and it's effect on ballistics

The bullet has already left the barrel , when you experience recoil. You don't feel push, from the bullet, as it leaves the barrel. It's already gone.
So no effect on ballistics. the energy in the recoil was generated while it was in the barrel.
Ported barrels channel some of the exhaust of blast upward and take some energy out of recoil, but the bullet has already gone. imo

 

[DaleA]

They did this and found the machine [the trebuchet] had less range than when allowed to move freely.

I saw a similar show, (I think it was on public TV) where the guy had a large model of a trebuchet on wheels. When he locked the wheels so it couldn't move the range was less. Same projectile each time because it was a model and they were doing it indoors. They showed a diagram where the weight powering the trebuchet moved in an arc, when the whole machine could move the real path of the weight was almost straight down and so it was more efficient and the payload went farther.

http://www.stormthecastle.com/trebuchet/trebuchet-physics.htm

https://www.youtube.com/watch?v=BfRxMuFA4ww

 

[Jimro]

There will be a difference in velocity, but not much. Other than that no change. The mass of the rifle already massively outweighs the bullet so essentially increasing the mass of the rifle to "infinite" has very little effect on how much energy can be pushed out the other end of the rifle.

As far as firing a bullet from a moving airplane, the bullet will always leave the muzzle no matter the direction the firearm is pointed because from the firearm frame of reference it is going zero miles per hour with reference to the airplane. After all, right now our planet is rotating at thousands of miles per hour but feels like it is standing still to us.

Jimro

 

[DaleA]

After all, right now our planet is rotating at thousands of miles per hour but feels like it is standing still to us.

Obviously you and I participated in different activities last night.

 

[Jimro]

Obviously you and I participated in different activities last night.

You don't have a problem until all your loved ones sit you down in a circle, tell you they love you, then try to help you deal with your behavior....

Until then, you're good.

Jimro

 

[Bucksnort1]

DaleA,

I believe that is the show.

 

[Bucksnort1]

Tinbucket,

What you write makes sense for this reason. When you watch Gun Gurus or R. Lee Ermy where they shoot all manner of weapons, they show some of the shots in super slow motion. You can clearly see the bullet leaves the barrel before the shooter recoils from the shot.

 

[tangolima]

Ballistics is a big word. What exactly does it mean in this context here? Muzzle velocity, point of impact, or even felt recoil?

There must be reaction force when the projectile is being accelerated down the barrel. It is not possible that recoil happens only after the bullet has left the muzzle.

-TL

 

[zukiphile]

When you watch Gun Gurus or R. Lee Ermy where they shoot all manner of weapons, they show some of the shots in super slow motion. You can clearly see the bullet leaves the barrel before the shooter recoils from the shot.

Yet the shooter isn't really the issue. The bullet and rifle will necessarily accelerate in opposite directions as soon as the bullet moves. Effectively changing the mass of the rifle will influence its movement, but not whether it moves at all.

A rifle is distinguishable from a trebuchet because the movement of the trebuchet itself contributes to a more effective pitch in some of the same ways a baseball pitcher's movement allows greater speed and force than if he were required to keep his body and on pitching arm immobile.

 

[mapsjanhere]

Fixing the barrel in a solid mount does not change the physics. It just means that the energy is transformed into heat in the mount instead of kinetic energy of the rifle. The bullet doesn't care as long as the mass of the bullet is small compared to the mass of the rifle in the first place.
As recoil preserves impulse, mounting the rifle solidly just gives you a very large mass on the right side of the equation. The left side stays unchanged.
m(bullet) x a(bullet) = m(gun) x a(gun)
Things are different if you'd have a heavy bullet in a very light tube, in that case an unsupported tube would go flying while the bullet stays put (as in the case of cooking off ammo in the oven on Mythbuster; the cases went flying).

 

[MrBorland]

The bullet has already left the barrel , when you experience recoil. You don't feel push, from the bullet, as it leaves the barrel. It's already gone.

By the time the shooter perceives recoil, the bullet's gone. But the rifle physically begins to recoil as soon as the ejecta begins moving forward. As such, the muzzle has moved a bit while the bullet's still in the barrel.

If the rifle were perfectly clamped, the muzzle wouldn't rise at all while the bullet's in the barrel, so I'd expect the trajectory of the bullet to be a bit lower through it's arc.

 

[TXAZ]

The issue is conservation of energy.
If some of the energy is used to move the "projector" (rifle or trebuchet) then less is available to move the projectile (bullet or boulder).

 

[mapsjanhere]

If you do the math you end up with finding that the energy distribution between bullet and gun is inverse proportional to the mass ratio between the two. When you're shooting an 11g bullet out of a 4300g Garand 99.7% of the energy go with the bullet and only 0.3% are transferred to the gun, assuming a loosely held gun. Having it solidly in your shoulder will add considerably to the weight and reduce the transferred energy. Shooting from a fixed mount will therefore only add maximal 0.3% more energy to the bullet.