The Williams FP sight screws to the left side of the receiver. It is not a “clamp-on”: you will need to have the receiver drilled and tapped. The Williams FP-SW uses the same base that is used for the Model 70 Winchester … 70AP, but with a longer windage slide. Casual observation will show you that the 1911 series receiver is not cylindrical like the Model 70, the Schmidt-Rubin tapers from rear to front. The base of the FP-SW is “close” , but it really does not fit the 1911 receiver without some grinding to get the base to fit the taper of the Swiss receiver. If you don’t do this fitting, the gallows arm will not be perpendicular to axis of the bore. It’s not off by much, and some folks who shoot only casually may not even notice it. If you shoot with a small rear aperture, the aperture will appear as a “cat’s eye” instead of round because of the misalignment. Again, that may not bother some folks. I’m just picky.
If you look at the receiver for the K31, you’ll see that the bridge (back part of it) is not round at all, it is sort of a rounded inverted trapezoid. To mount a Williams FP-SW on a K31, you’ll have to do some serious grinding on the sight base to get the base to fit properly, and I would recommend also bedding it to the receiver with Marine Tex. Yes, I’ve done it … about ten years ago when I first decided to shoot my first K31 over the National Match Course. I used it for one season and then replaced it with a Redfield base for the International Sight. I have since replaced the Redfield International sight on that rifle with a John Wilkes sight, which fits the same base, has much more elevation and windage adjustment. The Wilkes sight is the grand-daddy of today’s RPA “Tracker” sight.
If you want a click-adjustable receiver sight for a K31, and you are not a“serious competitor” or you think you can’t afford the excellent clamp-on Swiss Products sights, the Williams is a worthwhile choice, but it’s not going to be inexpensive, either. The basic sight with screw driver adjustments is about $73, the sight with Target knobs is about $85, and add to that about $9 for the thumbscrew for the elevation slide lock, unless you want to be fumbling around for a small screwdriver every time you need to make an elevation change (even with the target knobs). So you’re close to $100 already just for parts. Add whatever the cost to do the drilling and tapping and fitting, if you’re not equipped to do that yourself.
USN Distinguished Marksman No. O-067