Your post brought back some sweet memories. I'm good friends with one of the original owners/developers of BKL mount. The letters are for each of their last names. The B is my bud; Bonnet. When he found out I had a bunch of air rifles he asked me to experiment with some of his new designs. What you have is something he made for one of my R9s. It had the 3 little bolts on the bottom but with one saddle on top, in other words one long piece. So it was like an extended model 263. Never moved but compared to the 263 it worked the same so it wasn't put into production. I think I still have one of those somewhere. And if you have an older BSA SS rifle, the rails are 14mm. I helped him develop those. He used my BSA SS, Silverstar and Goldstar as Guinee pigs. We took measurements from an old 14mm Bsquare mount and applied them to a 263 mount. The 463 was born. Now when I say "we" it was pretty much him as he's the engineer, I'm just the one with the rifles. Guys back on the old yellow forum would argue that they sent BKL schematics on how to build the 14mm mounts and I would just smile, I knew the truth. I still have a ton of BKL stuff when he would build them. He sold the business to Air Force and is now a professor. Thanks for your post.
