off-center scope mounting

[broomjm]

I have a question that I'm hoping more experienced long-range shooters can help answer. I inherited a gun that my father sporterized from a 7.7X58 Arisaka. Along with the walnut stock and turned-down bolt handle, he fabricated what seems to be a very sturdy scope mount. However, the mount is off to the left, approximately 2" from the line of bore. I've shot the gun a few times and had no difficulty sighting it in or getting decent groups from it.

My question is: What will the left-of-center scope mounting mean for shots beyond say 275 yards?

 

[Varmint Hunter]

If sighted in @ 275yds I'd suspect that all impacts beyond that distance would be to the right of your point-of-aim. Not a good idea for shooting at any long range but shoud work fine for muzzle to zero range.

 

[Buffalobob]

If it is offset 2 inches to the left then it will shoot two inches right at twice the distance it is zeroed at.
If you are zeroed at 275 yards then it will be 2 inches to the right at 550 yards. It will be four inches to the right at 825 yards -thrice the zero range.

 

[sharpshooter1]

Wouldn't the rifle shoot 2 inches to the left at 500, if you are zeroed @ 250? I would think of it like an X, with the bottom left end of the "x" being the scope, the bottom right of "x" is the rifle, the center of "x" is where it is sighted in at. Wouldn't the top left side of "x" where the bullet would impact?

 

[murf]

I'm with sharpshooter on this one, impact will be to left of line of sight beyond zero point. Good analogy on the X thing sharpshooter!


Murf

 

[EddieHarren]

Sounds to me like whoever set that rifle up had an eye dominance situation. Many shooters never check to see which eye is dominate. Often a shooter will struggle with poor results and find out that all along, they've been trying to shoot with their right eye and they are actually left eye dominate. The answer to this is an offset scope. This arrangement allows a right handed shooter to use their left eye to shoot. I hope I understood, correctly, the scope mount you mentioned.

 

[Buffalobob]

Sharpshooter

You are right! It is the line of sight that is to the right not the bullet. The bullet would be to the left.
Thanks for the correction.

 

[sharpshooter1]

I mean, that is of course not worrying about drift due to bullet twist.... I don't know how that would affect it..... /ubbthreads/images/graemlins/smirk.gif

 

[broomjm]

So, if I wanted to shoot further than my original zero range, I would need to start holding to the right of where I wanted to impact? Given this gun's fairly limited choice of bullets and nominal velocities, I probably shouldn't shoot past 300 yards anyway.

Thanks to all of you for your input!

 

[broomjm]

The scope was mounted off-center due to the design of the bolt and action...the only other option was a forward-mounted design with a LER scope.

 

[EddieHarren]

"The scope was monted off center because of the design of the action and bolt"

In that case disregard my response. I recently installed an offset scope mount for a customer who suffered from the malady I described. It has greatly improved his shooting.

 

[metau]

Another option would be to 'zero' it in a little off. ie- if the centerline of your bore is 1.25 inches to the right of the centerline of your scope, then have the rifle shoot the same 1.25 inches to the right of where you are aiming at for a compensated zero. Do elevation the same, but just change the horizontal aspect of it. Then you wouldn't have to worry as much about cross-over. Just a thought.

Jerry