Magnum percussion caps vs. standard

my understanding is you should use Magnum percussion caps with black powder substitutes such as Pyrodex

Magnum caps fit differently than standard caps so there may be times you really want the standard caps for the proper fit of certain guns.

sigwally said:

"Hotter" with a little more priming mixture in there I guess. Or a slightly different stronger mixture, but...Why?
Are there situations where I should be using a Magnum cap, like below freezing wheather, or are some types of Black Powders harder to ignite? !

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They're used for better reliability.
For example, some rifles can have a problem with ignition because the flash channel has a right angle built into it that requires the flash to travel farther to reach the powder.
That coupled with using some substitute powders, or a substitute of a larger granulation can cause a misfire or a hang fire.

Magnum caps aren't usually needed with revolvers because they have a more direct ignition, with the powder abutting the nipple flash hole.
Yet some folks do prefer additional reliability such as when loading paper cartridges, or for hunting or self-defense.
777 powder has been considered to be somewhat harder to ignite but you usually never hear anyone complain about it other than in rifles.

You would think that magnum caps would always provide more certain ignition.
But if they don't seat properly on the nipple, they might also prevent the hammer from hitting with enough force to set them off.

On page 83 of DaveEhrig's book "Muzzleloading for Deer & Turkey", he lists some information on percussion caps and primers.

#11 standard cap - 6.53 cc of gas at 3,024 degrees F when fired.

#11 magnum cap - 7.59 cc of gas at 3,717 degrees F when fired.

U.S. #2 musket cap - 14.36 cc of gas at 3,717 degrees F when fired.

#209 shotgun primer - 21.98 cc of gas at 3,024 degrees F when fired.

#200 rifle primer - 11.68 cc of gas at 3,024 degrees F when fired.

I don’t like them for revolvers. They increase hammer bounce and cap jams. For rifles with substitutes, I could see them being helpful. That said, I buy what I can find, and I usually find magnum caps.

Some folks complained about cap shrapnel from using them with revolvers which makes wearing safety glasses even more important.