The only full bore ignition issues ive had with BH209 was with loose sabotless bullets i was trying out. They also hit very low and recoil was much less. Adding a felt or fiber wad helped but not enough to continue the experiment at that time.

Im not very impressed with the SD/BC of 50cal bullets in the 300gr range. IMO i would stick with what worked and IMO 350gr for a 50cal should be a better choice if it shoots well.