thanks for the thoughts on this. It's about what I was thinking.
What bothered me is if the accurate arms use a hotter primer than the 209,
why doesn't it have problems moving the charge before ignition?
Any one know of aftermarket breech plugs other than the 25 conversion for H&R or Encore?
If you are talking about the Ultimate, it uses a .45 magnum brass case over a nipple that extends all the way up into the case primer flash hole and seals itself against the back of the case. There is absolutely no blowback, even on the inside of the case. They have a patent on this design, or I would have already machined one for myself.
As far as primers go, 209 primers have been improperly coined as being the hottest primer in muzzleloading. They are not the "hottest" as in temperature, there is just more of a charge in front of the actual primer. The "Large Magnum Rifle Primers" that the Ultimate uses actually burn about 10 times hotter than a 209 primer. The 209 primer has a much bigger charge, and therefore can actually move a bullet out the barrel, by itself. The LMRP is just much hotter, and is like shooting a column of molten lead into the charge. They call it a "controlled detonation", and because of the pellet's hollow design, they can get fire to all the pellets at the same time. This is unlike a conventional ignition, where you ignite the column of powder/pellets at one end, where it must burn from one end of the column to the other. Knight's "Power Stem" breech plug puts the fire into the center of the charge, therefore getting a much cleaner burn.
If you ever get the chance to see the Ultimate in person, ask them to show you the cut-away of the .45 case that slips over and into their breech plug, that is the only way most people can understand what is going on. There is nothing like this design in the muzzleloading industry, and they have had that design for around 10 years, maybe longer. I just seen them again less than two weeks ago, the breech plug design is the exact same thing as the rifle I seen around 10 years ago. If you get it right the first time, there is no need for improvement, and they nailed it with their design.