Help - ring height

[SouthBayTommy]

I'm looking to upgrade the scope on a Howa 1500 308. It has a standard two piece picatinny base.

My current scope has a 1" tube with 40mm objective. The rings are "low" with .61" height. There is about 3 mm of clearance at the bell.

The new scope has a 30mm tube with 50mm objective. It seems that I need to add .20" (5mm) to the .61" ring height and I should be okay.

Is my calculation correct or am I missing something?

I'm looking at Vortex Pro Series rings which would be the Low size but most of what I'm seeing is 50mm objectives need high rings.

I'm so confused.

Thanks for your help!

[kcheung2]

The nominal size of the objective lens isn't the same thing as the outside diameter of the objective bell. Measure your existing 40mm scope and it's likely about 45mm across. Likewise many 50mm scopes are about 55-62mm outside diameter. Half of that is about 28mm, or 1.1 inches or so. And for the Vortex Pro rings, that matches up to the 1.26" for the High rings leaving about 0.1" clearance, or 3mm.

[SouthBayTommy]

hi kcheung2, it makes sense now.

as you can tell i'm a complete newbie and your help is greatly appreciated.

thank you!