I am alergic to Weaver bases but, it seem the path of least resistance. The rifle is a commercial post war FN large ring. It came with weaver bases #20-front and #26-rear. The Nikon scope I want to use wants to be about 3/8" to the rear. The bases are too far apart for that. I would like to move the front base groove to the rear. The # 20 is a short one with 1/2" between holes. I would perfer the longer base with the groove to put the ring even with the back of the receiver ring. will need to use medium height rings.

When I used to mount scopes for pay, we had a handy chart with the radius, height and hole spacing. Weaver now has only a dumbed down version for make and model. It specifies, #45 and 402. OK, maybe. I would like to know what I am getting before I order them though. Anyone have link to that old handy chart.

I would prefer a good mounting system like Redfield, or Control. They all seem to have longer spacing between holes in the ring.

Anyone figured this out?

Use extension rings instead of messing with the bases. Or get a one piece Leupold base which has a shorter span, and/or extension ring. Easy solution, I always use one piece bases to avoid what you are going through.
People bad mouth Weaver mounts, but they work, and return to zero. The Army didn't adopt them for no reason (Picatinny rail is nothing but a Weaver with specific notch spacing). But they don't look as good as a Leu or Redfield which is why I don't use them either.

I found a chart! The numbers on the bases are not the same as what weaver uses now. I would prefer a 1-piece base. They seem to have hole spacing on the ring longer than what I want. If it come to it I will make a base from scratch. Extension rings are fugly. Not an option.

This is a common rifle. The old sears and monkey ward 98s were the same. It might be that the holes were added later. The close spacing on the ring seem suspicius. I would think there is and easy solution if FN drilled and tapped it.

I don't understand the problem. is it the length of the mount or the hole spacing in the mount?

402 is just a long front base with the groove further back.

also you can get solid steel grand slam or steel Warne bases.

if the hole spacing is standard but there isn't enough "grooves" you can fab a two piece from a one piece. I did this for the height as well as the spacing of the rings for proper eye relief.

please excuse the millett rings they've been replaced :-)

It is not a problem, a puzzle. The bridge hole spacing is 0.504". All of the normal bases use 0.860". I now think it was made without holes. Somebody drilled and tapped it, but did it wrong.

The extension rings shown above won't work with the weaver bases I have on it. The Weaver tip off extension rings are ugly IMHO. So, I guess I could live with the scope too far foreward, drill one new hole, or see if I can get a good one piece base without holes.

I have a Control base that could work if I put an extra hole in receiver ring. The hole spacing is a smidge off between the rear receiver ring hole and one on the rear bridge. maybe JB weld up the gap.

If you wanna play around with bases, here's a list of .504 bases. (from gunsmithing kinks book)

Thanks for the help. I ended up machining a one piece rail base that was too high. I set up a fly cutter the proper radius and ran the mill up-down until the thickness was right. This allowed me to make and extension front base. Looks good and fits right. : )