Colts rail section is very different from Rugers rail. Go to GOOGLE and search IMAGES of Colt Rail gun and Ruger Rail gun. First, after you stare at them for a bit you will notice 2 major differences but there are 4 differences that will effect holster fit between manufacturers.
The first is the spacing and location of the picatinny rail slots. Colt has 4 slots from the trigger guard to the end of the dust cover. Ruger has 3 but the slots start much further forward of the trigger guard and the rail also ends in front of the ball turned section of the front of the slide. FYI, Picatinny rail slots are .206 wide and the rail is .182" if I remember correctly.
The second is the dust cover width just above the rail. On a Colt the dustcover is basically the same thickness as the slide (about .92") and is then reduced to the colt standard frame width (I believe .750") just before the slide lock. On a Ruger the dust cover is the same thickness as the frame at .765". Thats a difference of at least .15" which is a lot!
The third is the ejection port. Colts are rolled more at the front outer side whereas Rugers drop straight down.
Fourth and probably least important but sometimes comes into consideration for holster makers and thats that the Colt front sight is flush with the front of the slide. Rugers are slightly further back.
When you're "boning" a holster all of these physical differences make all the difference between fitting and jambing your gun in a holster.
Originally Posted by bwinters
kraemer list a holster for a colt rail gun.