Where Do Rifles Shoot By Themselves?

how was the rifle held when it was zeroed? if a shoulder was put to the stock when zeroed, the poi will be lower when fired in free-recoil.

think of a revolver vs. a semi-auto. the revolver front sight is very tall while the semi-auto front sight is very short. the revolver muzzle rise is much more than the semi-auto muzzle rise because the revolver barrel in recoil pivots on the wrist while the semi-auto barrel in recoil slides straight back. same principal here.

murf

Bart B. said:

I think there's two basic schools of thought in this conundrum:

One is the rifle and bore stays motionless until the bullet leaves the barrel.

The other is the rifle and bore axis starts moving before the bullet leaves the barrel.

Are Newton's laws applicable?

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The barrel does not stay motionless as the bullet travels down the barrel. That has been experimentally proven, and measured.

All you ever wanted to know about bullet jump.....

The Line of Fire (LOF) is a line connecting the center of the muzzle with the aimpoint on the target, where the aimpoint is defined as the location on the target to which the muzzle points, i.e., the boresight point. The LOF defines the origin for the jump vectors all the jump angles are measured relative to the angle of the LOF.

Muzzle pointing angle: The angle between the gun muzzle at the instant of shot exit and the pre-shot LOF when the trigger is pulled.

Muzzle crossing velocity: The angular deflection of the trajectory produced by the gun muzzle transverse velocity. This angle is computed from the arc-tangent of the ratio of the gun muzzle transverse velocity at the instant of shot exit to the projectile exit velocity.



Bullet motion starts at approximately -0.75 ms.



To answer your original question: The bullet strikes the target at a location equal to the sum of all the jump components.

I have done just that before and placed additional targets at 25, 50, 75 yards that the projectile passed through on the way.

The bullet impacted where it was aimed.



If the barrel is moving before the bullet exits, wind blowing too hard or shooting at extreme changes in elevation, just correct the aiming device for the difference, then you'll be back to POA=POI.

Shorter range but better light for the camera.



If barrel movement could not be accounted for, no one could ever hit a bullseye.

Is your hypothetical free recoil like an artillery hold? If it's bolted down, it will not shoot same POI as if held by muscle and bone.

We have all gone to the range with our buds and our zero'd rifles with a scope and they will not shoot to the same spot as we do. They see the same bull in the same cross-hair, but their hold is different from ours.

Always cracks me up in the movies when someone picks up a rifle from a fallen, and just puts rounds into amazing places as intended... Yeah, sure, you betcha

That's why every soldier has his individual battle zero for the rifle he's issued. At least it used to be that way

In a parallel universe where rifles are sentient beings

All rifle barrels move backwards and their muzzle axis points back and forth in different directions before bullets leave them.

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Yet folks have come up with methods that enable them to achieve repeatable points of impact relative to the same points of aim.

Like the rest of the sentence you were quoting.

...wind blowing too hard or shooting at extreme changes in elevation, just correct the aiming device for the difference, then you'll be back to POA=POI.

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Depends on where the rifle's center of gravity is relative to the barrel bore. If the cog is in line with the bore it shoots to the proper height. If the cog isn't in line with the barrel then the rifle rotates about the cog. Rifling in the barrel adds axial rotation about the bore. Again, cog determines axial movement, if it symmetrical about the bore no effect. Difficult to make a rifle with the cog perfectly centered and carry it in the field.

That is one thing I think the AK tried to do. Get the COG closer to the axis of the bore ...

jmorris said:

Shorter range but better light for the camera.



If barrel movement could not be accounted for, no one could ever hit a bullseye.

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Jump components are not always consistent.

Otherwise, explain why all the bullets do not go through the same hole in an indoor, windless range?

You hit the bullseye because the size if the bullseye is larger than the circular probable error.

Jump components are not always consistent.

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This is true, there are some things that would never make it 100 yards much less hit a target or center of a target.

redneck2 said:

I can assure you that a rifle/shotgun fired from something like a lead sled can impact at a significantly different point than when fired off a bench.

I bought a lead sled so that I wouldn't get beat up by my 870 shooting 3" Copper Solids. It was so far off as to be useless.

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In 12yrs of using a sled for nearly all my bench work, I've never had that problem.

When I shoot from a benchrest it has always been my experience that POI slightly changes depending on whether my shoulder is snug to the butt of the rifle or loose. It seems to me that inconsistency here is one of the things that creates a vertical string. It also seems more apparent in lighter weight/heavier recoiling rifles then in heavier weight/lighter recoiling rifles. Now keep in mind that I don't know this to be a 100% proven fact but seems to be true for me. Now, this could actually be caused by some other inconsistency in my bench rest technique but I don't think it is. It also seems to vary depending on whether my non trigger hand is holding the forearm of the rifle ahead of the front rest or is tucked underneath holding the rear bag. Possibly also dependent upon how far rearward the forearm is in the front rest, as it changes the arm of the recoil motion around the balance point of the rifle. Once again, I don't claim to know any of this to be a universal fact, I'm just sharing what seems to be the case for me and that by keeping these factors in mind and consistent tends to shrink my groups from the bench.

JohnKSa said:

Yes they are. And that means that the rifle begins moving in recoil as soon as the bullet begins moving. It also means that the school of thought that says the rifle stays motionless until the bullet leaves the barrel is incorrect.

However that doesn't necessarily imply muzzle RISE. Depending on the circumstances the gun could, theoretically, recoil straight backwards which would be recoil motion without any muzzle rise.

It is not possible to answer the original question with only the information provided. It will depend on where the moment of inertia of the system is relative to the recoil vector in both the case where the rifle is held normally and shot and when it is shot without being touched.

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That assumes the barrel is a perfectly rigid beam, with absolutely no flex, which is impossible given the barrel is made from an elastic material.

I once watched a dozen people shoot a 5-shot group with the same ammo in the same rifle resting it on one or two bags on a bench top. Groups ranged from 3/4" to almost 2". A plot of all groups centers measured 2-1/2".

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I have witnessed this same phenomenon myself years ago and after also passing around an XP-100 I had, I ruled it to be caused by how people were holding the rifle.

Even guys that had a hard time with the rifle were dead on with the pistol.

That said this problem is eliminated if the rifle mount is repeatable and "shoots itself" without being "messed up" by a human.

Much of this discussion only serves to prove how critical consistency on the part of the shooter is.

Bart B. said:

I would guess a fourth or more of all rifle shooters think that statement's cattle crap. They think the rifle doesn't move until the bullet is out of the barrel

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Those are the people who didn't take high school physics, or who learned their science from Road Runner. Like when you run off a cliff you hang there a moment before you start falling.

Newton didn't say "for every action their is an equal but somewhat delayed reaction."