I had the same problem with my DISC and Win209. To fix it:

First you need to have the concave breech plug.

Second, drill the flash hole to .040''. From the company it should be approx 0.033''. Also let say every 20 shots, clean the flash hole.

I had these advices from the Ing. who developted the BH209 and that fixed the problem.

Salar