Just went through this with my GBL.
I used the included shims for my XS lever rail by mounting them in the middle of the rail for my forward scout scope. Raising the rear got me on target.
I measured the shims with a caliper and relieved material from the underside of the front of the rail back to the front mounting hole equaling the shim height.
Back to the range and it was still dialed in.
See these threads:
http://www.marlinowners.com/forums/index.php/topic,84648.0.html
and
http://www.marlinowners.com/forums/index.php/topic,84847.0.html
Appears to be a rather consistant issue of late.
I used the included shims for my XS lever rail by mounting them in the middle of the rail for my forward scout scope. Raising the rear got me on target.
I measured the shims with a caliper and relieved material from the underside of the front of the rail back to the front mounting hole equaling the shim height.
Back to the range and it was still dialed in.
See these threads:
http://www.marlinowners.com/forums/index.php/topic,84648.0.html
and
http://www.marlinowners.com/forums/index.php/topic,84847.0.html
Appears to be a rather consistant issue of late.