Alsatian

I bought some scope mounts for a new rifle yesterday. The clerk asked me how close I wanted the line of sight to the barrel. I answered as close as possible. It now occurs to me that there might be a preferred height which is NOT as close to the barrel as possible. Any comments?

For example, I think I can make a good argument that it would not be desirable for the line of sight even with the barrel at the rifle. In my analysis, this would reduce the point blank range of the rifle. For illustration purposes, suppose the line of sight is 1.5" above the line of the barrel at the rifle. The bullet must travel some distance before it rises above the line of sight -- maybe 35 yards. If you are defining your point blank range based on 3" above or below the line of sight, then you have an additional distance X that the bullet travels to attain 3" above the line of sight and then drop to 3" below the line of sight. Thus, starting with your barrel 1.5" below the line of sight adds 35 yards -- the distance travelled before first attaining the line of sight -- to the point blank range.

Is there a distance of the line of sight above the barrel which is considered optimal? Of course, if you have any cant in your rifle hold -- where the scope/barrel alignment lists off to the side rather than being vertical as intended -- this causes problems, more problems the more the line of sight is separated from the barrel -- but the solution there is don't cant.

gorse

Interesting thread. I must disagree as to the non-desirability of having the centre of the sights (or scope) coincide exactly with the centre of the bore. Of course, this is impossible, but as a theoretical exercise, it is useful. The reason I disagree is that any issues as to the line of sight/ point-blank range, in a practical sense, would be offset (I think, more than offset) by the inherent advantage of absolutely no parallax in the system (at least, no parallax between the centre of the bore and the centre of the scope). I'm not referring to optical parallax, in the scope itself. But, this sort of arrangement would allow sighting along the closest possible axis, coincident to the bullet's path. I think that the point-blank range issue would be rather a moot point, in practical terms. Further, issues like scope cant, as you mentioned, would not exist.

Certainly, the sighting system in such a rifle could be adjusted to give a zero at whatever distance is required (within reasonable limitations). The point-blank range would exactly coincide with that distance, whatever it is, rather than the point of coincidence being simply the second point in space where the bullet path crosses the line of sight. I think that it would be desirable (and optimum) for those two points to coincide exactly on the target. Now, if you are referring to a non-adjustable system....that is, the sighting device cannot be adjusted to give a zero at different distances, then the max. point-blank range would still coincide with the bullet's path at the target face - BUT, there would only be ONE distance at which the rifle could be zeroed, based on the exact ballistic characteristics of the cartridge used. That would certainly not be satisfactory...and in the real world, with variations between different rifles...likely unworkable.

An interesting mental exercise.

bigbulls

You have a point in the MPBR however it will be soch a small advantage to have it 2 inches rather than 3 inches that under field conditions you will never notice it.

However, the higher you mount the scope the farther you must hold your cheek off the stock in order to see through the scope. This is highly undesirable as it will cause inaccuracies because you will not be holding the rifle as securely as you should. So the MPBR advantage you may gain mounting the scope higher will be negated by you being less accurate.

Another thing to consider is that when you must hold you cheek off the stock it hurts more when you fire the rifle.

The fact is that most all factory stocks are not made properly to allow a shooter to really snug up into the rifle and be able to see through a scope. Even a low power scope with a 20mm objective lense. So mounting one higher than needed simply causes uncomfortable and inaccurate shooting.

Run a 180 grain accubond at 3000 fps through a ballistics program and you will get these numbers.

With a 1.5 inch high scope.....
crosses line of sight at 28 yards
three inches high at 145 yards
crosses line of sight at 255 yards
three inches low at 299 yards

With a 2 inch high scope......
crosses line of sight at 35 yards
three inches high at 151 yards
crosses line of sight at 260 yards
three inches low at 304 yards.


So you gain five yards. Really not worth the other problems you would create.

thndrchiken

I've always used the rule of thumb that for 50mm objectives you use high rings, for 40mm medium, for 32mm low. Of course every gun and scope being different will ultimately dictate what size rings to use.

stubblejumper

I have always used the rule of thumb not to buy any scope that can't be mounted in medium leupold rings.

Soilarch

lets not over-complicate this. Like said before, the advantage of finding the exact "right" height won't ever be noticed...so with that in mind, I tend to think a scope 3" from my barrel is more likely to be snagged, bumped, upset handling etc. than one @ 2" THIS while unlikely, WILL be noticed when and if it happens...let that scope get some action from the action

One dumb-boys thoughts, for you...free of charge.