Different loads, different point of impact curiousity?

[SJPrice]

I know that different loads in the same rifle will cause a different point of impact. Common sense tells you it is so and the real world proves is true. I have never actually given it much thought until now. I understand the reason for the vertical change due to bullet weight, speed etc. but I am not sure I completely understand why the point of impact changes on the horizontal plane, with the exception of how wind acts on the bullet depending on speed, shape and weight. Given a "no wind" situation, what would be the reason for horizontal changes in the POI?

[J Miller]

I know that different loads in the same rifle will cause a different point of impact. Common sense tells you it is so and the real world proves is true. I have never actually given it much thought until now. I understand the reason for the vertical change due to bullet weight, speed etc. but I am not sure I completely understand why the point of impact changes on the horizontal plane, with the exception of how wind acts on the bullet depending on speed, shape and weight. Given a "no wind" situation, what would be the reason for horizontal changes in the POI?

Barrel harmonics. Different weight bullets cause the barrel to vibrate differently. Sometimes the vibrations will be such that the muzzle is at the point of vibrating to the side rather than top or bottom as the bullet leaves.
I've read that the harmonics follow a circular patter similar to the rifling.

Joe

[SJPrice]

Thanks for the response Joe. The reason I became curious was the similarity of 2 rifles and how the POI moved to the left almost an identical amount with the same 2 loads. The rifles are both Browning 1886's. One is a SRC with a 22" round barrel and the other is a rifle with a 26 octagon barrel. The loads in question were both factory loads. The one that both the rifle and the carbine were sighted in for is the Remington 405 grain express soft point. Then I tried some Garrett 45-70 420 grain Hammerhead loads. These are the 1650 fps loads, not the +P which is listed at 1850. In both cases the POI moved 2 inches down and one inch left at 25 yds. I found it curious in that the change was identical when so many other factors were different.

[J Miller]

You're right. Two different barrels doing the exact same thing with two different types of ammo. Could be I'm all wet on this one.

One other thing I've noticed in hand guns, especially .45s, is torque. With the bigger bullets and heavier loads the guns will twist around in your hands. I'm wondering if something like that might be a factor in yours?

Joe

[adirondakjack]

Once I was in a particularly self-mutilating mood and read Fackler on this. His explanation is that yes, bullets essentially fly through the air in a "dutch roll" much as a fighter plane tries it's darnedest to roll in a straight line but always has a bit of wiggle, esssentially screwing through the air as if working it's way along a lazy spiralling path.

Even with one bullet weight, changes in charge will cause changes in velocity which can cause a bullet that "used to" hit dead on at a certain range to suddenly hit an inch low and an inch left.... Changes in bullet weight increase the effect.

If Fackler is right, and I suspect he is, were we to take that same "1/2 inch left and 1/2" inch low" load and shoot it at a different range (let's say 175 instead of 200 yards, or 15 instead of 25), we MIGHT see the horizontal strike move left or right a little As well as of course vertically, as in effect we're at a different point in the path the bullet follows (think of a pitched baseball. Where it is in relation to an imaginary "string" stretched from pitcher to home plate varies a bunch over the flight of the ball, both side to side and vertically. A bullet is less dramatic, but this illustrates the idea.)

[Malamute]

Interesting comments.

When being a spotter for shooting at the 600 yard plate in hot weather, you can see the bullet's air distortion trail, and it looks like it spirals. Not sure why it does that, but this thread made me think of it.

[Tycer]

Interesting comments.

When being a spotter for shooting at the 600 yard plate in hot weather, you can see the bullet's air distortion trail, and it looks like it spirals. Not sure why it does that, but this thread made me think of it.

Exactamundo! You can see the spirals of a barrel being shot when filmed in super-high-speed video capture played slow. I was told it has to do with that exact phenomenon in the barrel. Different harmonics of that spiral in the barrel cause different flight paths hence different POI.

I never found the video I was looking for.

http://www.youtube.com/user/29426129#p/u/10/FaW_Hs0B79c
http://www.youtube.com/watch?v=L_E_GJay ... r_embedded
http://www.youtube.com/v/s5pVya7eask&rel=1&border=1
http://www.youtube.com/watch?v=xeeeFxA_9nA

[Ben_Rumson]

I have often seen this spiral in WWII gun camera footage when the tracer rounds take flight...IRC German B&W footage. As mentioned above torque...Somewhere around here I've got before and after pics in an old A R magazine of Elmer K. shooting a rifle from the shoulder chambered for 50 BMG... First pic is him aiming.. Second pic he's pushed back on one leg.. the other leg raised a foot or so off the ground... the rifle has torqued completely out of his supporting hand...and raised up about half way to his hat...He said it didn't kick too bad....

[Chuck 100 yd]

Torque ,,, The gun starts to recoil before the bullet exits the barrel. Different loads and different recoil impulse. The gun also twists due to torque before the bullet exits the barrel.

I don`t know how to figure it out but just how much horse power does it require to take a bullet from 0 to 300.000 rpm in 2 or 3 milliseconds The gun will move and the impact too.

[adirondakjack]

To experience gun torque, fire a heavily loaded .44 mag or .45 Colt revolver using your left hand only. The RH twist causes the barrel to twist to the shooter's left. Not as noticeable when shooting right handed, as turning the hand toward the midline of the body is a natural movement. When fired left handed, the hand rolls toward the back of the hand, away from the body's midline. It's creepy.

[darkwater]

Interesting comments.

When being a spotter for shooting at the 600 yard plate in hot weather, you can see the bullet's air distortion trail, and it looks like it spirals. Not sure why it does that, but this thread made me think of it.

Exactamundo! You can see the spirals of a barrel being shot when filmed in super-high-speed video capture played slow. I was told it has to do with that exact phenomenon in the barrel. Different harmonics of that spiral in the barrel cause different flight paths hence different POI.

I never found the video I was looking for.

http://www.youtube.com/user/29426129#p/u/10/FaW_Hs0B79c
http://www.youtube.com/watch?v=L_E_GJay ... r_embedded
http://www.youtube.com/v/s5pVya7eask&rel=1&border=1
http://www.youtube.com/watch?v=xeeeFxA_9nA

Sweet...must be why they put heavier barrels and/or harmonic dampeners on target rifles...the less movement, the better accuracy.

[El Chivo]

changing bullets seems to affect the windage more than changing powder

[adirondakjack]

Interesting comments.

When being a spotter for shooting at the 600 yard plate in hot weather, you can see the bullet's air distortion trail, and it looks like it spirals. Not sure why it does that, but this thread made me think of it.

Exactamundo! You can see the spirals of a barrel being shot when filmed in super-high-speed video capture played slow. I was told it has to do with that exact phenomenon in the barrel. Different harmonics of that spiral in the barrel cause different flight paths hence different POI.

I never found the video I was looking for.

http://www.youtube.com/user/29426129#p/u/10/FaW_Hs0B79c
http://www.youtube.com/watch?v=L_E_GJay ... r_embedded
http://www.youtube.com/v/s5pVya7eask&rel=1&border=1
http://www.youtube.com/watch?v=xeeeFxA_9nA

Sweet...must be why they put heavier barrels and/or harmonic dampeners on target rifles...the less movement, the better accuracy.

That's corect. BUt all that said, with careul load development, inching along in small steps, along with all the necessary stuff for CONSISTENT ammo, even "whippy" barrels can be made to print well. My pencil barrel (original 1918 barrel) 8MM Mauser holds 3/4 MOA with a recommended handload, and I'm not all that particular about brass prep, etc. But if I let it wander by 1/4 grain charge, or seat em .010 different, the group not only opens up, but the center of the group moves in a more or less "clock face" manner (might go to 2 oclock, or 10, etc).

[SJPrice]

Great discussion and thanks for all the replies and information. I never noticed the torque from shooting heavy revolvers as I shoot left handed and so it has always just felt natural to me. I think I will load some lighter, as in 300 grain cast loads and see where they print in comparison to the 405s and the 420s. I may also try some leverevolutions I have on the same target. Might prove interesting with these two Browning 1886(s). I will post the results if anyone is interested.