Rifle Scopes Scope zero vs Base MOA

[XLR]

Question for the optical savvy. Are most scopes designed to be in the middle of their elevation adjustment with a strait base? All my rifles are currently running 12-42x nightforce scopes and I have found that with a 20 moa base, it puts the elevation adjustment almost on the bottom allowing almost full upward adjustment (45 moa). If I were to change ot a 32x nightforce which has 65moa of elevation adjustment, would a 30 moa base be needed to put the scope close to the bottom of its eleavtion adjustment? Thanks

 

[One-Eyed Jack]

Re: Scope zero vs Base MOA

Where the erector is in the tube depends on where the scope is looking -- it can be anywhere in the tube on a flat or canted base.

If the erector is looking straight ahead (along the optical bore line of the scope) when it's in the middle of the tube, then it will look down (bullet "up") by about 4-5 MOA when you zero the scope with a 308 at 100 yards with a flat base.

If your NF scope has 65 MOA of total elevation travel, you can use a 30 MOA canted base and still zero a 308 at 100 yards. You will have approximately 57 MOA of bullet "up" elevation. If you are at your 100 yard zero, then you will have about 8 MOA of "down" elevation left.

 

[Switchblade]

Re: Scope zero vs Base MOA

Cant is the rifle leaning left or right. Scope bases are SLOPED.

Scope erector travel will give extra MOA in upward travel since the base is sloped on a 20 or 30 MOA sloped base. For a typical 308 a 20MOA sloped base is fine for 1200M if you can hold for that range.
If you move to a 338LM you would want a 30MOA sloped base for the extra range.