I heard Tom Post put a positive stop before the powder chamber in his small cal builds. His powder chamber in those small cal builds was necked down like a brass case would be on a center fire cartridge. Im not sure what the purpose for necking down the powder chamber was, but im sure he had a reason. One reason for the stop in the barrel was that it stopped the bullet from going past the shoulder at the end of the barrel and into the powder chamber. If the bullet could go past that shoulder, it would get hung up and cause a catastrophic event. The other purpose for the stop I heard was to allow for some airspace in the powder charge. Im not sure what the purpose of the airspace was, but im sure tom post had a reason. Unfortunately I heard Tom post doesn't build muzzleloaders anymore and only builds sizing dies now.
I heard someone else mention that they have a 30 cal smokeless build with a large powder chamber. They said they were using H4350. They were told by their builder that they were NOT TO GO BELOW 55gr. of powder. Im not sure why they had a minimum powder charge but I certainly believe what the builder said. Their load was 62 gr. of powder with either Hornaday or Berger 150 gr flat base target bullets. They said with a 100 yard zero, it would cover 500 yards with 7.25 moa at 3250 fps. The bullets were full formed to the barrel. Ive heard with calibers below .40 , obtration into the rifling becomes a major problem. So full forming bullets in a sizing die becomes a necessity.
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