Well, actually #11 caps do ignite BH209 but not instantaneously. They create a hang fire similar to a really poorly tuned flintlock. My tests were with an MK-85 with a #11 TC Flamethrower using RWS #1075 plus #11 caps on an 80 degree F day. I do not recommend using BH209 outside the recommendations on the bottle, but I just had to try it for myself.

I have a Ruger 77/50 but I have not tested BH209 in it. On the back of the BH209 bottle they show a "not approved" 209 breech plug that is very similar to the breech plug design used in the Ruger 77/50 209 conversion kit from Cabela's. I may tinker with it in the future but for now I am very satisfied using T7 in my Ruger 77/50 with #11 caps.