I hear “new” Rem Arms 870 shotguns that come factory drilled and tapped for an optic base have 3 holes vs the 4 hole set up that Remington earlier used on some 870 and 1100/11-87 guns.

Is the 3 hole spacing the same as the 4 hole, just omitting the front hole?  If not, does anyone have the actual measurements for the 3 hole spacing?

Several sources are reporting that the 3 hole spacing is the same as the original 4 hole spacing, just omitting the front hole.

I have a couple of those rails.  None of the manufacturers could tell me a critical bit of info:  the mounts come with 3 short screws and one longer one, which hole does the long screw go to?!  Yes, I could just try it and check if it interfered with anything internal.  But why no definitive info from the makers?  Are the 3 screw mounts screws all the same length?

Paladin