I purchased a Ruger SP101 with a 3 1/16" barrel for home protection after a break-in. I couldn't be happier with the firearm, it is a great, reliable gun! When I decided that Iwould start OCing I had a problem. I could not find a holster that would fit!! There were tons of holsters made for the SP101 2 1/4" barrel, but not the 3 1/16".
Hopefully this will help anyone who has the same gun.
There are many holsters which state that they are made for a small frame 2 - 3 inch barrel revolver, but that extra 1/16" does come into play even though you wouldn't think. And most of the holsters that are 3 - 4 inch revolvers, are for large frame and the SP101 is lost in it.
The perfect OC holster for the SP101 w/ 3 1/16" barrel is the Gunmate Ambi Hip Holster #21128. Gunmate's 28 size is for medium size revolvers with 3 - 4 " barrels. The SP101 fits great! Also, for under $15, you can't beat it!
The holster I had before the Gunmate is a good fit after a slight modification. Also, it is better as a CC holster than an OC holster. It was a Soft Armor size 26 (small frame revolver 3"). The barrel was a little too long and it did not sit down in the holster properly. Once I cut the stitching and opened the bottom and let the barrel come to the end of the holster, it fit snug.
Hopefully, this was some help for someone else.