How do the Seekins Ring clamp to the rail?? Does it only clamp to the outside of the 1913 Rail, or does it have a slot in the middle to rest inside one of the slots on a 1913 rail as well? I cant tell from the picture on their site.
There is a cross lug that fits into the pictainny slot and rail grabber to clamp onto the outside of the rail, it's really pretty much the same as most other rings on the market.
You shouldn't need to lap them, I never had an issues with ring marks or anything with the two pairs that I had. I will say though that unlike some other scope rings where the tube just kind of falls in, the tube is a tight fit in the Seekins rings. I don't really see this as a bad thing but it may give you the impression it has to be lapped when in reality it's just the way the ring is.
One little thing of note that I just ran into today actually - the 1" rings use T15 screws on the ring caps, as opposed to the T25 that the 30, 34 & 35mm use. All the rings use T25 on the clamping screws.
Had to make a quick run to the local hardware store to pick up a T15 bit for my torque wrench.