Anyone know the distance between the holes? Thanks

Is this a mount that predates factory drilling? Other than that I'd say the hole spacing is what was set by the factory.

I think it's for D&T receivers. My old 250-3000 has a .80 hole spacing and I'm wondering if yhat mount would fit. The recommended front mount does not fit my spacing. Closest match is a #86 Weaver which I have not tried yet.

The separation of the factory drilled holes is 1/2"

It sounds like you have a gun that was drilled for the old Redfield mount that predated factory drilling. I have those old mounts if that is the case.