Rifle Scopes Do you measure the front or rear on a rail??

[GSRswapandslow]

I have an EGW 20moa rail...i'm trying to figure out ring height and am measuring everything...and I came across something that I'm confused on:
EGW states their rails are between .4 and .45" thick....mine is .425" (10.795mm) thick, AT THE REAR. Wouldn't the front be the important measurement, since the scope slants downward? The front measures out to 0.281" (7.15mm)

My scope (viper pst) is 2.441" (62mm) with the BC cap on it..

so with that said:
using rear thickness
(.425+.820)-(2.441/2) = 0.025"
not a lot, but clearance is clearance according to Seekins

using front thickness
(0.281+0.820)-(2.441/2) = -0.119"
obviously, this does not work now....

If I chose to go to the lows:
rear thickness
(.424+.0.925)-(2.441/2) = 0.130"
this works with more than adequate clearance but raises the scope a bit...not a lot, but more than 0"

front thickness
(0.281+0.925)-(2.441/2) = -0.014"
now...this wouldn't work WITH the BC cap..but without, it would...or maybe just sand down the BC cap some to fit...no biggie


so...back to my question, do you use the front or the rear of the base to figure up your needed ring height?

 

[glock24]

Re: Do you measure the front or rear on a rail??

Definitely use the front of the rail.

Also, I would forget about using the rail thickness alone, and instead take a measurement from the top of the rail to the top of the barrel. This measurement, plus your ring center-line height is more realistic to your actual scope's position over the barrel.

Also, depending your barrel contour and scope length, you will usually end up with additional space because the barrel tapers away from the very end of the objective bell.

<span style="text-decoration: underline">Example;</span> (below picture)

Top of rail to top of barrel = 0.290"
OD of objective bell = 2.085"
Ring center-line = 0.820"

(0.290"+0.820")-(2.085"/2) = 0.0675" clearance (calculated). It is obviously more than this due to barrel taper.

 

[GSRswapandslow]

Re: Do you measure the front or rear on a rail??

so...taking a straight bit and resting it level on the middle of the scope base gets me .444" to the thinner part of the contour, where the scope bell will rest.

i'm thinking the super lows will work