Just a quick question. Can the Burris P.E.P.R. mount be put on backwards? I have a Burris 2-7 scope mounted in one and at 50 yards with the elevation all the way up, I'm still hitting 18 inches low.
(By backwards I mean with the mount slanted back towards the stock.) This is on my .458 SOCOM.

My load for sighting in (50 yds) is as follows:
32 gr. H110
Hornady 300 gr. hollow point
WLP
Starline Brass

I've used this scope with Warne rings on my Marlin 1895 .45/70 at a 50 yard sight in and it's dead on.

I'm headed back out tomorrow with the scope reversed in the mount, but I was wondering if anyone else had experienced this.

Does the mount have built in elevation (i.e. 20MOA)? If not (and it's a 0MOA mount) turning it around will no effect on elevation.

The one I have is 0 MOA

If the 18" discrepancy is the result of mount issues then turning it around will at least confirm the issue is with the upper or mount.

I had a PERP mount and it was gtg. Might want to just try moving it forward or back to see if that 18" discrepancy between POI with max scope adjustment changes (if it does all signs point to an issue with the flat top upper.) Then try turning it around to see if it changes (POI should change if the issue lies with the mount/should not change if the issue is with the flat top.)

If you have another mount or even a pair of adequately high weaver/picatinny rings you should try those too.

Still had the same problem after swapping the mount around. Further inspection is showing that the bullets are hitting the flash hider (bored out M60).

There is a piece of metal in the threads that is causing the bullet to just crease the side. I think its a piece of the old M60 barrel. I'll be looking into removing it later tonight.

Tomorrow I'll re-fire the sight in rounds without the flash hider to see if that's the problem.