Once in a very great while, i would experience a hang fire with my Accura. What totally cured the rare hang fire, was to make the CVA breech plug look more like the Omega breech plug i.e. on the powder end create a powder pocket.
Pictured is a home made breech plug made from a grade 8 bolt. Thus far this breech plug has provided 100% ignition whilst using BH209 with all kinda primer. This breech plug hasn't been tried in sub-freezing weather, nor sub-zero weather yet, but it is getting cooler here day by day.
Last winter after hunting season, there was quite a discussion about modifying breech plugs to receive a vent liner. This i did to my CVA breech plug, and whilst doing it, created a powder pocket. This modified OEM plug provided 100% reliable ignition in my Accura with BH209 all last winter. The rifle was fired after being left loaded and dirty in the cab of the truck, overnight, in sub-zero weather many times. Even in temperatures colder than -10*, there was never a hang fire using W209 primer.