Steve: "the standard 10 gauge load is 4.25 drams BP and 1-5/8 ounces of shot" for modern replica MLs?
Drew, I stand corrected and believe I am in error using the words "the standard 10 gauge load". The actual words cut and pasted from Circleflys website are:
"Service Charges in Shotguns: The British service charges for breech loading smooth bore guns, as listed in W.W. Greener’s book, “The Gun and It’s Development” (9th edition, published 1910)" along with a chart referencing the load I gave.
Given this information the referenced load is for
breech loaded guns. Using black powder I wouldn't expect any load differences between muzzle loaders and breech loaders, if there are differences (perhaps because of primers) I'd be interested in learning about them. In the field, I found that the 12 gauge BP load I used in my 10 gauge gun worked just fine on pen-raised birds, at least the birds didn't seem to notice any difference

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Steve