590 optic plate question

[baum9260]

I have a 590 thunder ranch with the optic cut out. I am mounting an osight se with the rmsc footprint. I was under the impression this should mounting directly to the gun however when I attempt this it doesn't sit flat as the screw holes protrude from the gun and the optic isn't countersunk. There were 3 plate adapters included. The one maked 5L seems to resolve this. Is the plate supposed to be used?

 

[The_Shmoo]

The Mossberg website says RMSc footprint should be a direct fit. Is there like a gasket or shim you're missing? How far out is sitting? I'm not really familiar with the osight, but I'd reckon the sight being out of spec over the mount being out.