Tilting your rifle...bullet flight path?

[Jimro]

Bart B.,

I've read that. The issue is that they are looking only at the small amount of arc at the top, so it doesn't address what we are talking about for extreme cant.

But trust me on the effect of gravity making the points of impact elliptical and not circular. Although a circle is just a special form of an ellipse. The line of bore will make a perfect circle that is centered around the point of impact, and you can easily measure that using a laser bore sighter.

Jimro

 

[Mobuck]

Regardless of the effect, the "accuracy" of a tilted rifle will be most affected by the lack of precise replication of position. If your accuracy requirements are very loose, probably OK. Sight lines closer to bore lines and short range=not a big diff.

 

[Bart B.]

Jimro, I agree the downrange group is eliptical, but across less than a 2 degree spread of the bore axis, it's minimal. The LOS is only 35 MOA away from the LOF for my 1000-yard example at any cant angle.

 

[Jimro]

Bart B.,

I probably got stuck on stupid, but one of the sniper training objectives someone mentioned was being able to calculate your hold over when laying on your side and shooting from under a car...

Suffice to say that it can be done, but no one really wants to do it at any sort of distance as you can run out of scope real quick using holdovers.

Jimro

 

[Bart B.]

That under car sniper also has to hold off horizontally in the direction the rifle's bottom is at.

 

[Boncrayon]

It's really all about gravity and NOT sight line. To tilt a rifle, you still have to account for the forward energy of the bullet as it is leaving the muzzle and the gravity force from the vertical ground.

 

[Bart B.]

????????

 

[g.willikers]

Has no-one mentioned the effect of the spinning of the earth?
Are you guys slipping or what?

 

[Bart B.]

No, they haven't

It's effect is negligible up to 1100 to 1200 yards. It's masked by other ballistic and atmospheric variables to difficult to easily correct for. No top ranked long range competitor I know of ever gave it a thought. I never did, either.

At longer ranges, it does have an effect. US Naval shipboard gunfire control computers calculate for it. As they also do for deck tilt (cant, for land lubbers). I operated and maintained one of those monsters in the late 1950's. All done with simple high school trig functions. Smaller numbers are used for rifle fire but the same stuff happens.

At target range, the muzzle points somewhere above the aiming point. The bullet drops some distance straight down below that point to hit where the site's aim at (microscopic coriolis and spin drift amounts ignored). If the rifle's canted to one side, that point where the muzzle points rotates in a circle to one side and a little below level from its original position. The bullet now drops straight down the same amount below that point. Bullets drop the same amount if the rifle's canted 90 degrees, but now from a point straight out horizontally from the rifle. If the muzzle pointed 35 MOA above the aim point originally, then canted 90 degrees, the muzzle now points 35 MOA to one side and bullet drop will be the same from that point down.

A 100% trig function. Calculate your own:

http://www.jbmballistics.com/cgi-bin/jbmmpm-5.1.cgi

Read this article for a good explanation in detail:

http://home.kpn.nl/jhhogema1966/skeetn/ballist/kantel01/kantel1e.htm#_Toc449514675