Interesting Question?

[dreever]

On my .308 I replaced the Seekins .30mm .92 height rings with Badger 1.125 height rings to get a bit more barrel clearance. Which amounts to .205 higher scope mounting.
Here's the question: All things being the same how will this effect my 100 yard zero if I make no re-zeroing adjustments. Will bullet impact be higher/lower by how much, or will it stay exactly the same?

Danny

 

[6BRonwheels]

Hi Danny,
Based on my calculations, the bullet should strike .1" high at 100 yards, .3" high at 300 yards etc.

 

[BoydAllen]

If you have ever lapped a set of rings, you know that even the high priced ones do not show a perfect cut without some work, so this is strictly a theoretical answer, as if the scope was perfectly mounted in the first case, and the only difference was that it was .205 higher in the second. It will print .205 lower, at all distances, if you don't touch the scope. Now we know that the scope mounting was probably not perfect in either case, so, as I said, this is strictly theory.

 

[gunsandgunsmithing]

If you have ever lapped a set of rings, you know that even the high priced ones do not show a perfect cut without some work, so this is strictly a theoretical answer, as if the scope was perfectly mounted in the first case, and the only difference was that it was .205 higher in the second. It will print .205 lower, at all distances, if you don't touch the scope. Now we know that the scope mounting was probably not perfect in either case, so, as I said, this is strictly theory.

Not so,Boyd. The difference in line of sight and center of bore changes and the angle of correction will change to accommodate it. It won't change the POI by much, but,theoretically speaking, it will change. Check it with a ballistics program that allows changing the sight height. Think about it like this...the barrel must be pointed upward to make the paths of the bullet and the crosshairs intersect. If you move the scope but not the barrel, you will change where they intersect.--Mike Ezell

p.s.-the shorter the distance to the target, the more difference it will make

 

[SS427]

Wouldn't it have the same effect as if you raised the reticle .205 higher, which would lower the impact of the bullet that same amount at 100 yards?

If you make a 4 or 8 click, one inch adjustment at 100 yards, that equals a two inch change at 200 yards and a 1/2 inch change at 50 yards, right? I could be wrong, but wouldn't that mean a .205 change at 100 yards equal a .410 change at 200 yards?

 

[BoydAllen]

I was referring to what would happen if no scope adjustments were made, which, if you reread the question, what he asked. Without a scope change, the angle stays the same. It would be as if one simply lowered the bore .210, with no other change. This is a parallel repositioning, not an angular adjustment since the relationship of the bore and scope base is unchanged, and no scope adjustment done.

 

[gunsandgunsmithing]

I was referring to what would happen if no scope adjustments were made, which, if you reread the question, what he asked. Without a scope change, the angle stays the same. It would be as if one simply lowered the bore .210, with no other change. This is a parallel repositioning, not an angular adjustment since the relationship of the bore and scope base is unchanged, and no scope adjustment done.

But we're not talking about a PARALLEL repositioning. Because the bullet begins to drop as soon as it leaves the barrel, and he has an established 100 yard zero, the bore centerline is angled upward in relation to the scope centerline.(this is actually being done with the scope internally). Without angular difference between scope and barrel, he'd be way low; starting at being low equal to scope height and increasing with distance. We are "lobbing" all bullets at the target,regardless of caliber to some degree. So the barrel and scope can't be parallel. I agree with you that if they were both parallel, the difference would be the amount of change in scope height. Key words here are that he had an established 100 yrd zero, and for all practical purposes, that's all that matters because nobody shoots without being zeroed at some distance. At any distance greater than .000 from the muzzle, there will be an angular difference between the bore CL and scope CL if you want to hit what you're shooting at.--Mike Ezell

 

[BoydAllen]

Guys,
For purposes of illustration, lets say that I hold the scope in a rigid fixture, so that it can not move. Then we attach to it a barreled action with the lower rings, and adjust the scope so that the bullet hits exactly where the scope aims at 100 yards. (I know that using a scope for a point of attachment will not work.) Now, with no other change, I lower the barreled action by .210, by substituting taller rings. The scope is still on target, but the barreled action has been moved so that its bore is parallel to its original position, but .210 lower. Since the angle of the barrel has not changed a second round fired will be .210 lower on the target. The trajectory is unchanged. Now at a longer distance, if you start with the scope adjusted so that with the lower rings the bullet impacts precisely where the scope is aimed. and you do the same ring change, the point of impact will still be .210 lower than before, at the new distance.

On the other hand, if the conditions of the problem are changed so that the scope is re zeroed at 100 yards after the ring change. and we consider the down range situation (still zeroed at 100 yards), the point of impact at say 200 yards will be higher with the tall rings than with the short ones. I fact, if you use a good external ballistics program ( I have Quick TARGET.), and play to scope height, going well above any reasonable mounting height that would be practical in the field, you can get to a place where the points of impact for 100 and 200 yards are at the same height with no adjustment. If you don't believe me, try it, before you jump to a conclusion.

 

[rbertalotto]

Boyd, I do believe you have this one correct!

Using a ballistic program can easily resolve the answer as Boyd stated..............

Fun little problem for a freezing rain night!

 

[BoydAllen]

;D

 

[gunsandgunsmithing]

Boyd, My apologies to you. Amazing what a mental picture can do to help a tired mind see the light. I actually think we started out in agreement and I then got sideways somehow. :-[. Oh well. Sorry and thanks for setting me straight.--Mike