scope height above receiver

[Bart B.]

Yes, figure 3 ain't right. Bullet drop at target range must be measured from the line of fire point above the line of sight. A 100" drop at 600 yards requires the LOF point 100" above point of aim where the LOS intersects the target. Bullet drop below the horizontal at target range is virtually the same for reasonable amounts of cant. But bullet drop from the LOF at target range is the same regardless of cant angle.

Here's my version using a clock face that shows exactly what happens with a bullet having 100" drop from LOF at 600 yards:



Maximum ordinate (MO, high point of trajectory above LOS) for zero cant is almost 30 inches at 350 yards for a 600 yard zero for the bullet used to calculate data for.

Note the drop below horizontal below the red line for different degrees of cant. As the sine of 30° is .5, note the 30° cant moves the bullet impact half of 100 inches; it's 50 inches to the right and several inches low. And those 5 bullet holes' plotted arc is the same arc as the clock face has at its edge.

That very same figure 3 is shown on a popular web site for accurate shooters:

http://www.accurateshooter.com/optics/canting-effect-on-point-of-impact/

Too bad it's not correct. Not surprised that nobody has seen fit to delete it and replace it with good stuff. In it, Brian Litz says a 1° cant will produce five inches of lateral displacement at 1000 yards with "common cartridges." A bullet with 286.5 inches of drop from LOF at 1000 does that. It takes a 7mm match bullet of 168 grains leaving 3200 fps to do that; 7mm Wby Mag, for example. Is that a common cartridge?

I'm not surprised that so much bad ballistic data's made public. It's equal to the Flat Earth Society continuing to tout the earth is not round and trying to prove it

 

[RPZ]

To me the scope height is only significant in obtaining a firm cheek weld on a harder kicking rifle. And it's affect on zero and points of impact at ranges less than zero and past zero for practical shooting be it hunting or self defense. The closer to the bore the less the difference will be at distances shorter than zero and shorter distances beyond zero. Cant is something that can be all but eliminated with propper scope mounting where the vertical post/posts are as close to being perfectly vertical as possible. Any error is not going to be an issue in practical shooting, or apparent unless you are shooting bench rest or 1000 yard competition.

 

[Sniper66]

What is the max height a scope should sit above the reciever on a varmint rig? Will mounting lower make for easier shooting? I have a 700 VLS and am debating using a stock pad to get proper alignment on a "tall" scope vs going with a scope that sits lower on the gun. Any thoughts?

I have two Remington 700 varmint set ups, a VLS .243 and a VSF .223. Both have low mounts. The VLS has a Leupold VX-III 4.5-14X 40mm and the VLS has a Bushnell Elite 4-16X 40mm. Both are wicked accurate with my hand loads. I very much prefer low mount. It works for me and to my eye it looks better too.