"The British Military load for the brown bess was 125g of powder with an extra 40 grains for the pan for a total of 165g per cartridge. the powder from the original cartridge I saw was course like 1f, Ive fired this combo from a repro french 1727 and it shoots well using the 1f as the priming powder, the only draw back is it burns slow in the pan so you have to watch your follow through".
Gunpowder now is not the same as gunpowder 300 years ago. I personally would not be loading 125 grains in any hand held gun. Whether or not it is proofed for such a load is not the point, the point is that there is no need for such a high load as this with modern gunpowder.
1Fg is cannon grade gunpowder, and I have no idea what it was doing in an original 18th century Brown Bess cartridge, unless (a) it was a mistake, or (b) they had run out of the regular gunpowder. Either way, just because it was done, does not mean that you should do it!
For those of you not familier with modern gunpowder/Black Powder, 1FG is a large grained gunpowder made for cannons. 2Fg is generally for any caliber over .45 but can be used in smaller calibers. 3Fg is for .45 caliber & smaller, but can be used in larger calibers with a load adjustment, i.e. the smaller the grains of powder, the higher the internal pressure. So if you are using a recommended load of 2Fg, DO NOT use the same load when using 3Fg. Use less. 4Fg is made these days as a priming powder. 4Fg is a very fine grain gunpowder and should NEVER be used as a main charge. You may also find it interesting to know that 300 years ago there were no priming horns made or used for hand held guns/rifles. The same gunpowder used as a main charge, was also used to prime the pan of the flintlock.
1Fg being a large grained gunpowder used only in cannons, would be very slow to burn if used for priming. I really can't see the British army and navy using 1Fg gunpowder as a standard in the Brown Bess.
Long Land pattern Brown Bess.
Paper cartridges made for smoothbore muzzle-loading guns.