Howdy
You will have a little bit of trouble mimicking the original Black Powder 45 Colt load with modern brass because modern Solid Head brass does not have quite as much powder capacity as the old copper, folded rim, Benet primed cartridges did, or the old Balloon Head cases did.
The two cases that have been sectioned in this photo are an old Balloon Head case on the left and a modern Solid Head case on the right. You can see how the older case could hold more powder than the modern case can.
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The original loading in 1873 was 40 grains of powder under a 250 grain bullet. This is what they looked like. You can see from the cutaway photo why they were called 'folded rim'. The priming was internal, sandwiched between the rear of the case and an anvil plate pressed into position inside the case. There were two flash holes that allowed the flame from the priming compound through the anvil plate to ignite the main powder charge. These cases had the largest powder capacity and were the only ones that could actually contain 40 grains of powder without compressing the dickens out of it.
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Anybody that feels The need to add to this needs his head examined. Great job, D.
The Balloon Head cases pictured above would only hold about 37-38 grains of Black Powder.
I use a 250 grain Big Lube bullet in my 45 Colt rounds, but because the powder capacity is so much less I only put around 33.5 grains of powder into each case before seating the bullet.
Not saying you cannot stuff 40 grains into modern cases, but you will be compressing the powder a lot more than was originally done.
Loading Black Powder into cartridges is actually less fussy than loading smokeless. As long as the powder is slightly compressed, that's all you have to do. Unlike Smokeless, where an extra grain or two with some powders might turn a cartridge into a bomb, Black Powder has much less energy than Smokeless. So a grain or two or three more or less really will not matter.
I have a Remington 1858 with a 45 Colt conversion cylinder, and I can tell you that I don't really care to shoot full house 45 Colt Black Powder rounds in it. The grip shape is just different enough from a Colt that I find it uncomfortable with a 45 Colt stuffed full of powder. I prefer to shoot 45 Schofields with about 28 grains of powder under a 200 grain bullet in my Remington.
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I prefer to reserve my full power 45 Colt Black Powder rounds for my Colts, the recoil is more comfortable with a Colt.
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Anyway, all you have to do is pour in enough powder so that when the bullet is seated it will compress the powder by between 1/16" and 1/8". That's all there is to it. You can weigh the powder if you want, but unlike Smokeless, not all Black Powder weighs the same.
I made this chart up years ago. It shows the actual weight for a few of my favorite charges of Black Powder with reference to Lee Dippers. Notice Elephant, which is not made any more, weighed the most, Goex the least, and Schuetzen about in the middle. It really does not matter how many grains you put in, just pour in enough so that when the bullet is seated it will compress the powder by between 1/16" and 1/8". That's all there is to it.
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Here is a little trick I used to use years ago. I made a little ruler with a small stick. I placed the stick so its end was at the crimp groove of a bullet, and made a mark at the base of the bullet.
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Placing the stick in a case with the mark even with the case mouth I poured in enough powder so the base of the stick was covered by about 1/16" of powder. Simple, that's all there is to it. By the way, those are my wife's long fingernails, not mine.
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Or you can scribe a line on the outside of the case with your calipers representing where the base of the bullet is when it is seated. Then you simply eyeball the powder charge to make sure it is slightly above the scribed line on the outside of the case.
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Here is what goes into my 45 Colt loads. 2.2CC of Schuetzen FFg under a 250 grain Big Lube bullet. This charge gets compressed about 1/16" when the bullet is seated. You can see on my chart it is about 33.3 grains.
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Any Large Pistol primer will be fine, I usually use Federals, but I have used Winchesters in the past. I have no experience with those Remington primers. Contrary to common belief, magnum primers are not needed for Black Powder. BP ignites more easily than Smokeless and magnum primers are not needed.
I also have no experience with Olde Enynsford but I can tell you that all other things being equal, you will see between 60fps and 100fps more velocity when using FFFg instead of FFg. I used to use FFFg in my 45 Colt, 45 Schofield, 44-40, and 44 Russian ammo, reserving my FFg for 12 gauge shotgun, but I stopped stocking two different granulations years ago and only stock FFg Schuetzen these days for everything, including 45-70.
You will want to be a bit careful about what type of bullets you use. BP wants a soft, gooey bullet lube. Generally speaking, modern hard bullet lube on modern hard cast bullets tends to create hard caked fouling in the bore that becomes difficult to remove, and ruins accuracy pretty quickly. It can also tend to cause the cylinder to bind up more quickly. You have probably noticed that your 1858 Remington binds up pretty quickly with BP fouling because the cylinder lacks a bushing on the front to shield the cylinder pin from fouling blasted out of the barrel cylinder gap.
I used to pan lube regular hard cast bullets years ago with a mixture of about 50/50 Crisco/beeswax. But the skimpy lube grooves on modern bullets did not carry enough lube. It was OK for pistols, but in a rifle length barrel the bore became starved for lube about 6 inches from the muzzle and had to be swabbed out to restore accuracy. I tried all the standard tricks, lube cookies, wads, lube on top of the bullet. Way too much work.
That's why I went to the Big Lube bullets years ago. They have huge lube grooves and carry enough soft, gooey bullet lube to keep a rifle barrel lubed its entire length, and keep a revolver rolling without the cylinder binding. On the left is one of my 44-40 rounds and on the right is one of my 45 Colt rounds. Next to each is the Big Lube bullet I use with them. I have stripped the lube out of one bullet to show how huge the lube groove is.
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Here are the bullets I use for BP. The four on the left are all Big Lube bullets for 38-40, 44-40, 45 Schofield, and 45 Colt. The big 405 grain 45-70 bullet is more of a traditioinal design, and all way on the right is one of my old pan lubed 45 Colt bullets. Notice how skimpy the lube groove is.
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Anyway, that's all there is to it. Don't sweat the last grain or two. Pour in enough powder to be compressed about 1/16" to 1/8" and seat your bullet. Did I mention that's all there is to it?