As long as you are using a good hot primer in a sealed breech plug, snug fitting bullet, a heavier obturating bullet, and getting a good burn, you will have less problems.
I was testing #11, SPP/SPMP/SRP/SRMP, and over a dozen different 209 primers in every type of breech plug you can think of, and several you can't.
There is a dash of sulphur in the mix, and I'm sure a little of that goes long ways.
The breech plug that pitted, was from an anemic primer, leaky breech plug, large charge of powder, and a loose fitting light saboted bullet. Lots of powder residue in the bore and on the face of the plug. Add in extremely humid conditions, and it was a perfect recipe for a worse case scenario.
Believe it or not, a White Rifle #11 breech plug and a RWS 1075 Plus cap will ignite Blackhorn 209 in moderate temperatures albeit delayed and hang fires, but never once a misfire. I even got the 1075 Plus to light up a charge of Blackhorn 209 under 2 oz of #5's in the White Thunder/Tominator. The flame has a real short path to the powder. Wouldn't recommend it though.
I would also bet there are guys that have went months to a year in the right climate with a Blackhorn 209 fouled bore, with no problems?
You pays your money and you takes your chances!