Difference in POI between Mk V11 & Mk V1 ammo?

[Ridolpho]

Richard: Something weird about this- why would a rifle shoot way too low with higher velocity ammo than the sights were originally calibrated for? I've found exactly the same thing with a '96 MLE and a Citadel Martini Enfield- at least a foot below POA at 100 yards with Mk VII velocities. Also weird, I noticed the rear sight cap on another MLE ('98 and stamped HV) was substantially taller than the one on the first rifle. When I swapped them it yielded a near perfect zero (at 100 yrds) with any ammo I tried. None of my references seem to mention different sizes of sight caps and I would have assumed any recalibrations of sights for different ammo would have relied on different ramp profiles on the rear sight. I hope someone can explain this.

Ridolpho