Scope mounting height


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GarySTL
July 30, 2012, 08:53 PM
What effect does mounting height have? I understand that a high mount might have an effect on cant if there is any. But other than that I'd like to be educated.

I know my ballistics program has a place to input the height, but I never looked to see what changing the height input made.

A friend is concerned about too high a mount on his Ruger 10/22. I'm thinking that on a .22 it's ongoing to matter much.

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jmr40
July 30, 2012, 09:53 PM
The biggest reason is that having a scope too high, or too low for your individual rifle makes it difficult to get your eye lined up with the scope with the gun mounted correctly.

But there are other reasons that determine the bullets flight. The bore will always be lower than your sights and will always be pointed slightly up in relation to your line of sight. When you bullet leaves the muzzle it will be traveing up at a slight angle and will cross your line of sight at some point around 25-50 yards from the muzzle. It will reach its apex at some point and begin to fall back down. When it crosses the line of sight coming down, that is the range your rifle is zeroed.

If your scope is mounted 2" above the bore vs the typical 1.5" that means the angle the bullet takes to cross your line of sight the 1st time is sharper. For extreme long range shooting this can be an advantage. At typical hunting ranges it could be a disadvantage. An AR rifle with typical iron sights has the sights very high above the bore. If zeroed at 25 yards it will again be zeroed at 300 yards. Good for long range shooting, but it will be 6"+ high at 100 yards and about a foot high at 200 yards. It does not reach its apex until after 200 yards because the sights are so far above the bore. With a typical hunting rifle with the scope mounted lower you can zero at 100 yards and never have the bullet more than 1" above or below your line of sight from 50 yards to 150 yrds and only be 2-3" low at 200, about 8-9" low at 300.

The ballistics programs need this information to accurately calculate trajectory.

GarySTL
July 31, 2012, 08:48 AM
Thanks for the explanation. After posting my question I thought about it and realized that it was all about the crossing angle of the line of sight and bore.

I'm thinking that with a 22lr sighted at 25yd it not going to make much difference out to 100.

Thanks

One_Jackal
July 31, 2012, 09:32 AM
Another reason to use low profile mounts is life. By nature a scope mounted 2" high is going to get beat up more than a low profile mount. Nothing is more aggravating than walking through the woods and have a vine rip the gun out of your hands or bring you to an awkward halt.

sage5907
July 31, 2012, 10:15 AM
Another reason for mounting the scope lower is to be able to see the sight picture with the cheek firmly held against the stock. You don't want your head bobbing around like a bobble head doll. If you close your eyes and place your cheek comfortably against the stock and then open your eyes you should be able to see your sight picture. Also, the sight picture is affected differently with a higher mount when shooting prone than when shooting offhand or sitting because your body is leaning forward. It the last few years it has become fashionable to have a straighter stock with less drop at the heel which requires a higher mounted scope. BW

GarySTL
July 31, 2012, 10:33 AM
I guess he'll have to try it out and see if he likes it, if not he can get lower rings.

jmr40
July 31, 2012, 11:56 AM
As a general rule, as low as possible is best. At least on most hunting rifles meant to be shot from field positions. On rifles like AR's or many target rifles made with stocks designed for high mounted scopes then high is OK.

This is the problem with mounting really high on a 22. The trajectory difference probably won't be noticeable, but getting a good sight picture through the scope could be difficult. At least with a factory stock. Buying a stock designed for high mounts would be different.

TonyAngel
July 31, 2012, 01:26 PM
I wouldn't worry about the math when choosing rings. What I'd worry about is getting a height that lends itself to getting a comfortable and consistent cheek weld for you in the position that you shoot from most often.

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