I've just finished the "research" on the subject of canting. First draw is that the accepted models are plain wrong, a suspicion I had since my first post on this matter.

After looking at some papers, especially an excellent one written by Jeroen Hogema, a dutch gentleman, I started to see some discrepancies among the usual published stuff (in this and other forums) regarding the correct solution to calculate the effects of canting.

One thing that especially alerted me was the “fact†that vertical deflection was almost regarded as minimal and not to worry about…weird to say the least.

Also, I contacted Rubén Nasser ("Tiro Fijo") from Paraguay and a poster here.

So between Jeroen, Rubén and myself after a very enjoyable exchange of emails, the correct solution showed up.

In short, the correct solution MUST account for LOS and Zero Range, and thus VERTICAL DEFLECTION is an ISSUE.

So the right formula to account for cant is :

X(R)=H(R)*sin(cant)
Y(R)=H(R)*cos(cant)-DROP(R)

where H(R) is height of bore line with respect to sight line (as a function of range R)

I really don't want to make a tedious thread with many formulas, but if someone is interested, just let me know and I'll post them.

Example :

MV: 2900 fps
BC: 0.490
LOS : 2.0 inches
Zero : 200 yards
Cant : 10 degrees

Dist / H( R ) / X / Y
yards / inch / inch / inch
0 / -2.00 / -0.35 / -1.97
100 / 3.55 / 0.62 / 1.30
200 / 9.10 / 1.58 / -0.14
300 / 14.65 / 2.54 / -6.97
400 / 20.20 / 3.51 / -20.21
500 / 25.75 / 4.47 / -40.64

Get a hold of Derrick Martin's (Accuracy Speaks) book on shooting competitively with the AR-15.

Derrick is High Master, Distinguished, President's 100, etc, as well as making a living building competitive rifles.

His opinion is that cant isn't as important as a lot of guys think. He shoots a canted rifle, and shoots it quite well (I know, I've shot against him ).

I'll be the first to admit that the formulas above went right over my head (heck, I'm just a shooter... ), but in the real world, I know what some guys say who shoot way better than me.

Besides, I usually prefer the simplest method of acheiving a goal. I couldn't even begin to comprehend the formulas required. I just get my dope at the ranges I expect (or know) that I'll be shooting, and trust that.

(BTW, no disrespect meant to the above poster. I'm just giving another side to look at.)

Gus,

Actually, I would be interested in your formulas. If you would post them, I promise to wade through it all! I can do a little math myself! Anyone who isn't interested in tedious formulas doesn't have to read them! Thanks!

Gary

quote:

Originally posted by mudstud:
Gus,

Actually, I would be interested in your formulas. If you would post them, I promise to wade through it all! I can do a little math myself! Anyone who isn't interested in tedious formulas doesn't have to read them! Thanks!

Gary

Here goes the post in other forum of TiroFijo on the subject we discussed together and with Jeroen. Please let me know if I can be of further help

-----------------------------------------------

The basic formulas we are using are:

horizontal projection: X = drop*sin ß

vertical projection: Y = drop*(1 - cos ß)

ß = cant angle

I think these formulas should be pretty accurate for the small angles we are discussing, normal cant in LR shooting should be 6º or less.

The sight height has no effect when you zero the scope at any distance, since you are basically converging the LOS and bore line at that range, and then compensating for drop (see images A, B and C in this article: http://www.tirofusil.com/canting01.php )

When you cant the rifle you do it rotating on the LOS, so drop is the "diameter of the circle". This is normally done in target or long range shooting.

But when you have a hunting rifle you don't normally change the scope's settings, so you may take a shot at 400 m even if your zero is 200 m using holdovers. In this case the angle between LOS and bore line corresponds to the 200 m zero and the effect of canting would be smaller than if the rifle was zeroed at 500. The sight height does have an effect in this case.

The formulas Gustavo posted take this into account:

X(R)=H(R)*sin ß
Y(R)=H(R)*cos ß - Drop(R)

where H(R) is the height of bore line in relation to sight
line, as a function of range R:

H(R) = R/R0*(SH + Drop0)- SH

SH = sight height
R = range
R0 = zero range
Drop0 = drop at zero

quote:

Originally posted by Cold Bore:
Get a hold of Derrick Martin's (Accuracy Speaks) book on shooting competitively with the AR-15.

Derrick is High Master, Distinguished, President's 100, etc, as well as making a living building competitive rifles.

His opinion is that cant isn't as important as a lot of guys think. He shoots a canted rifle, and shoots it quite well (I know, I've shot against him ).

I'll be the first to admit that the formulas above went right over my head (heck, I'm just a shooter... ), but in the real world, I know what some guys say who shoot way better than me.

Besides, I usually prefer the simplest method of acheiving a goal. I couldn't even begin to comprehend the formulas required. I just get my dope at the ranges I expect (or know) that I'll be shooting, and trust that.

(BTW, no disrespect meant to the above poster. I'm just giving another side to look at.)

Derrick also "dials in" the windage to accomodate his cant at each of the distances he competes at. In other words, his sight are set specifically for each distance, and for his cant at the position he shoots from at that distance. I he did not do this, he would we having "windage" errors based on the degree of his cant.

I too know Derrick, he's a great competetor, gunsmith and a nice guy to boot.