Tom,
Did you drill the flame channel the whole way through the plug? I think that is a must and will now guarantee BH209 ignition with most plugs when that is done.
It is drilled and tapped all the way through, the same as a Rem 700ml Breech Plug.
I am really thinking that Spitpatch is correct in his assesment of the Vision BP having the larger 'flash channel' allows more room for expansion and therefore less blowback out.
This is an interesting assesment from another forum about the project...
I think in a rifle like an Omega the domed area around the flash hole would be the way to go. If you have ever looked into the mechanics of an explosion for demolition purposes you evidently understand the ideas behind focused explosive pressures. What your saying goes right along with all those thoughts.