How to work out which hight for mounts

[Dangermouse]

Before I depart with hard earned cash and get it wrong, can someone follow my idea and either confirm it is correct or not.

To find out the hight of mounts you need to stop the objective bell touching the barrel

Measure the outside diameter of the objective bell = a
Measure the outside diameter of the scope tube = b
Subtract the scope tube figure (a) form the objective bell figure (b) giving you figure c.

Measure the hight of your mounting rail. Ideally from barrel to where the scope mounts rest on the rail - not the top of the slots in the Picatiney rail, if you have them = d

If figure (c) is greater than figure (d) then that is the amount of hight that you need from your rings.

The only problem I can see with this is if you have a rail with MOA angle, ie as I have a 20MOA rail. This would cause the scope to be sitting at an angle to the barrel, not horizontal, and would bring the objective bell closer to the barrel.

Any thoughts?

DM

[Ovenpaa]

The inclination of a 20 minute rail is around a third of a degree so not a lot in the great scheme of things, you can either take the length of the scope add half the dimension of the objective bell and do the math or assume it is parallel and allow a minimum of 3mm clearance at the objective end.

Alternatively lay the rifle on its side, place the scope parallel to the rail with the objective bell as close to the barrel as possible and then measure the gap between the rail and the bottom of the 'scope and take it from there.

[lapua338]

Generally, I find that 50mm OBJECTIVES will almost always use HIGH rings in a given style. In certain instances, such as with extremely heavy barrels or some makes of firearm, SUPER HIGH rings may be necessary. 42-45mm OBJECTIVES will almost always use MEDIUM rings in a given style. In certain instances, 45mm scopes may require HIGH rings. 40mm OBJECTIVES will almost always have enough clearance with LOW rings in a given style, though MEDIUM rings will give slightly more clearance, particularly when using a barrel with a thicker shank portion or a heavier contour.
This is certainly true with Leupold and Warne rings.

[Dangermouse]

That sounds like a good rule of thumb but gets shaken about a bit when you start looking at Scopes with 35 and 40mm tubes!

Using the maths I mention above the IOR 9-36 X 56 would use the IOR low mounts, where as the Nightforce 8-32 X 56 would use the high NF mounts.

Not as simple as you might think, especially as much of the purchasing is done over the Internet these days.

DM

[Ovenpaa]

Well the Viking has an IOR and hefty barrel so I can measure the mounts if that helps any?

[Dangermouse]

I won't send you on a fools errand until I am ready to buy, but may ask later in the month,
Thanks,
DM