Howdy
First off, you are not going to blow up your pistol with a Black Powder load. Modern conversion cylinders are made of top grade steel and they can take the pressure developed by a full house Black Powder load. And don't worry that your barrel probably says For Black Powder Only, or something similar. The cylinder is the main pressure vessel of a revolver, not the barrel.
But I discovered a long time ago that I did not care for full house 45 Colt Black Powder loads in my EuroArms Remmie equipped with an R&D Conversion Cylinder for 45 Colt. The grip shape of a Remington 1858 is different than a Colt, and I do not care for the amount of recoil my full house Black Powder 45 Colt loads generate in a Remmie.
For what it's worth, my standard 45 Colt Black Powder load for my Colts is a 250 grain Big Lube bullet over 2.2CC (about 33 grains) of FFg Schuetzen in a standard 45 Colt case.
But for my Remmie I prefer a 45 Schofield case and a 200 grain Big Lube bullet. The Schofield case has less powder capacity than the 45 Colt case, and reducing bullet weight from 250 grains to 200 grains cuts down considerably on recoil. I put 1.9CC (about 28.5 grains) into a Schofield case (I buy them from Starline) and seat a 200 grain Big Lube J/P 45-200 bullet on top.
This photo shows the cartridges I load with Black Powder. Left to right they are 44 Russian, 45 Schofield, 38-40, 44-40, 45 Colt, and 45-70. You can see how much less powder capacity the Schofield round has than the 45 Colt round.
This is what goes into my standard 45 Colt loads.
This is what goes into my 45 Schofield loads.
Schofield rounds have a larger diameter rim than 45 Colt, usually .512 for the Colt round and .520 for the Schofield round. At first that was a problem with my Schofield rounds, but I had a gunsmith open up the counterbores for the rims on my cylinder so they will accept both rounds. I'm pretty sure that all the conversion cylinders can chamber 45 Schofield rounds now.
A few comments: Black Powder weighs different amounts, depending on what brand it is. It is not like Smokeless, where the density and weight of the powder does not change from lot to lot. That is why I usually specify my BP loads by volume, not by weight. I use the weight as a reference only. Ignore those guys who tell you not to weigh your Black Powder charges, they are full of hooey, there is nothing wrong with weighing BP charges. But because BP actually weighs a different amount from brand to brand, I made up this chart a long time ago showing the weights of my favorite BP charges. I use Cubic Centimeters as my standard volume reference because that is the way Lee powder dippers are set up. This chart is pretty old, Elephant brand powder has not been around for a long time now.
I changed over to FFg for all my BP cartridges a long time ago. Generally speaking, all other things being equal you will get between 60fps - 100fps more velocity with FFFg vs FFg. Less velocity means a tad less pressure. I simply got tired of keeping two different granulations around, and FFg has always worked fine for me in all my cartridges, including 12 gauge shotgun.
Compression: You must compress your powder. My rule of thumb is to compress the powder by 1/16" - 1/8" when the bullet is seated. So if you reduce your powder charge you must make sure you are still compressing the powder a bit. At the very least, make sure the base of the bullet meets the top of the powder charge. Don't leave any airspace in there.
Fillers: you can use fillers to take up some of the extra space in your rounds if you want. Most of the CAS guys use Grits. I experimented with corn meal years ago. I stopped messing with fillers a long time ago, too much extra work.
Bullet lube: What kind of bullet lube are you using on your bullets? Generally speaking, Black Powder needs a soft, gooey bullet lube, such as SPG. Using standard bullets with standard hard bullet lube can result in difficult to remove fouling in your barrel.
