The Side Mounted Scope on the 6.5 mm Carcano

[Bob Prudhomme]

To better understand the difficulties of sidemounting a scope on a rifle, there are a few more things about rifle scopes you should know. Look carefully at the following two diagrams:





These may look a bit complicated but are really quite simple. When a bullet leaves the muzzle of a rifle, the only force acting on it then is gravity, and it will begin falling to the earth. For this reason, to hit a target at 100 or 200 metres by aiming at it through a scope (or sights), it is necessary to raise the barrel up so the bullet will follow a parabolic curve to the target and impact the target on descent. The amount of elevation depends upon how "flat shooting" the rifle is. A rifle with a high muzzle velocity and a high ballistic coefficient will not require much elevation, while a low velocity round with a bullet possessing a low ballistic coefficient (the 6.5mm Carcano M91/38, for example) requires more elevation.

Quite often, on a hunting rifle, the line of sight will be adjusted until the rifle is able to hit bullseyes at 200 metres. This does not mean the hunter is specifically looking for game at 200 metres, although his rifle is sighted in for that distance. The purpose of this is that his rifle, at 100 metres, will only be shooting an inch or two high at the top of the parabola and this can be easily compensated for, much easier than trying to hit a target at 200 metres with a rifle sighted in for 100 metres. The results can be seen in this chart. Note how quickly the bullet begins to drop.


It is interesting to note, from the first two diagrams, that the bullet path will cross the line of sight just a few metres out from the muzzle, and again at the target. This actually means that a rifle sighted in to be accurate at 200 metres is also accurate at a few metres.

Now, while the trajectory of a rifle seriously affects hitting the height of a target at different ranges, and this was the inspiration for built in rangefinders on hunting scopes, the advantage of mounting a scope (or open sights) directly above the barrel of a rifle is that the left-to-right (windage) of line of sight to bullet impact relationship does not vary with range. In other words, if you aim at bullseyes at 50 metres, 100 metres, 200 metres and 300 metres, you will see a corresponding drop of the impact point of the bullets as you go further out but, unless you are shooting in a crosswind, there will be no variation to left or right on the target.

However, if you mount the scope on the side of the receiver, as on LHO's alleged rifle, you are no longer directly over the barrel. Even though it appears to be too small of a space to make much difference, the line of sight (from the scope) and the line of departure (bullet path) are now beginning from two different points, and the rifle can only be sighted in for windage to be accurate at one range and one range only; namely, the point at which these two lines converge. Any close shot made with this rifle will put the bullet to the right of the aimed at target, and any shot made past the convergent point will put the bullet to the left of the aimed at target.

Years ago, a friend of mine owned a Winchester Model 94 30-30 lever action rifle. It had open sights and was a great deer rifle in brushy ground. For some odd reason, my friend decided one day he just had to have a scope on this rifle, even though he was a deadly shot with open sights. As with the Carcano, it was necessary for the gunsmith to side mount the scope on the 30-30, not because of interference with the action but because this repeating rifle ejected cartridges straight up from the receiver, and they would hit the scope.

The gunsmith "boresighted" the scope after mounting it but, of course, it was still necessary to sight the rifle in at the range as boresighting only "gets you on the paper", as they say. It almost drove us insane trying to sight that rifle in so it would hit bullseyes at 100 metres. Every adjustment we made to elevation or windage seemed to throw us off somewhere else. It didn't help that the Model 94 is a very light rifle and likes to kick, and one is anticipating this with each shot.

During this exercise, I tried a couple of shots with the open sights, and found having the scope right in your face made this an extremely awkward and uncomfortable thing to do. As I said before, those who think the inadequacies of the scope would have prompted LHO to use the open sights during the assassination are as much as saying LHO never practiced at a range with this rifle. If he had, he would have removed the scope long before he brought the rifle to Dealey Plaza.