For what it is worth Burris told me to just mount the weaver style rings against the forward edge of the 1913 slot because it would hold up to recoil better mounted tight to the front. BTW, when I asked if they had an extension ring so I could mount the Burris scope on my A.R.M.S. mount, they said the mount must be made for red dot type scopes because it was to short to mount a full sized scope, they said the rail had to be 6.5" minimum. It's a nice piece of glass, but Burris puts their turrets well forward of center. Still trying to find a way to make this work. I should have got a Luppie or a Smith mount.