The MPX and MCX weapons have an OP rod and recoil springs above the bolt carrier. Therefore the rail is higher above the bore than an AR or SIG 516. The typical rail height above the bore on an MPX or MCX being higher than ARs is a price we pay for not having a buffer tube as part of a lower receiver extension.

The optical centerline being 1.5 inch above the bore sight number comes from bolt action rifles with telescopic sights. ARs have a gas tube and a picatinny rail above the barrel which increases the height of all rail mounted sights above the bore. My MCX has a rail about 1.5 inches above the bore, so sights are usually just under three inches above the bore.

I have read that the HK 416 and SIG 516 designs are somewhat similar as one designer worked on both designs. My 516's rail is about 1.25 inches above the bore. The piston runs above the bore and below the rail on the 516.

Bill

 

Thank you for the insights. I'm still trying to figure out the full exact measurements, but this is helpful. I'll likely need to contact some manufacturers to fish for some specs.