303guy,
See attached PIC of my 513SA factory mounted LYman 57 peep sight. I replaced the original
eyepiece with a Merit adjustable. It enables adjusting the size of the peep to get optimum focus on the front sight.
Also, full length pic of my 513SA. Had it since late '60s. Very accurate , accounted for lots of Prairie Dogs out to 165 yards.
--when equipped with the Weaver T10....
beltfed/arnie