b44mag, the Remington Kleen bore and the Winchester Triple7 primers are different than a standard 209 primer. They are not as hot as the standard shotgun 209 primer. The are intended to be used with triple7 powder. The reason for a less hot primer is to reduce the crud ring. If you plan on using Pyrodex or black powder, the standard 209 primer will be OK.
Now Winchester did come out with a 209 primer package the says muzzleloader on it, but it is just a standard 209 primer, so no need to spend the extra money on them.