Howdy
So by now you have realized that the actual length of your bullet, in particular the amount that protrudes into the cartridge case when seated, will determine how much powder you want to use.
I understand you needing to use the substitutes, many jurisdictions limit access to real Black Powder because it is classified by the BATF as an explosive, unlike the substitutes, which are classified in the same category as Smokeless powders. In many jurisdictions the storage requirements are different, and many retail outlets do not want to have to deal with the stricter storage requirements off real Black Powder. Even during normal times. All bets are off now that shooting supplies are so hard to find. I have always been able to find real Black Powder, but I do not look down my nose at anyone who has to use one of the subs because he cannot find any real Black Powder. I usually go in with a friend and we buy 25 pounds of powder from one of the wholesalers every year or two to take care of our needs. Even some of the wholesalers are having trouble keeping real Black in inventory right now.
Anyway, your Marlin has a strong action and can take a full charge of Black Powder with no problem. Whether you want to deal with the recoil is another question. With a full charge of powder, the heavier the bullet, the more recoil you will experience.
I do all my 45-70 shooting with a Pedersoli Sharps and an antique Trapdoor. Both are chambered for 45-70.
This is a photo of all the cartridges I load with Black Powder. 45-70 is on the far right. The others, left to right, are 44 Russian, 45 Schofield, 38-40, 44-40, and 45 Colt.
These are the bullets I use. Most are what are called the Big Lube bullets because they have huge lube grooves. The big 405 grain bullet is the one I use in 45-70. Notice it has several small lube grooves, each filled with a Black Powder compatible bullet lube. More about that in a moment.
Although I load most of my BP cartridges on a progressive press, I load my 45-70 rounds on my old Lyman Spartan single stage press. It is set up here to load 45-70. I use the hand priming tool shown to seat my primers.
This is my set of RCBS 45-70 dies. The piece laying horizontally across the top of the box is my compression die. More about that in a moment. You will want to use case lube on your cases, unless you have carbide dies, to keep your shells from getting stuck in the die.
My dies are steel and I use a light spray of Hornady One Shot case lube on my dies. Don't spray too much, a little dab will do ya.
I portion my powder out using a Lyman Black Powder measure.
I then pour the powder down a drop tube into a cartridge case. A drop tube is not absolutely necessary, but it helps settle the powder for a more consistent load.
Now, let's talk about powder capacity, bullet weights, and powder compression. Your new BP friends will tell you all about how much compression they like to put on their powder. This can cause endless arguments. Basically, with a Black Powder cartridge, you do not want to leave any airspace in the cartridge, you want the powder compressed under the bullet. The technique MEHavey described is good, it is the technique I use to determine how much powder to use. Let's just say for a moment that you want your powder compressed 1/8" when the bullet is seated. Measure from the base of the bullet to the crimp groove. Then make a little ruler with a narrow dowel and mark the distance from crimp groove to the base of the bullet. Like this. Yeah, this is a 45 Colt bullet but the technique is the same.
Then place the little ruler like this, with the mark at the case mouth, and cover the bottom of the stick with about 1/8" of powder. No snickering, those are my wife's lovely fingers.
That is how much powder you want for your particular bullet and 1/8" of compression. Pour the powder out and weigh it. Let's not fuss about grains/volume and all that stuff. Do this several times and weigh each charge, then average them. That is your powder charge for that particular bullet and that particular brand AND granulation of powder.
Your new friends will tell you how much compression they like. The really, really serious guys will compress the powder, then seat a thin cardboard wad on top, then seat their bullet
without further compressing the powder. I cheat a little bit. I set up my Lyman BP powder measure to pour out 70.0 grains of Schuetzen FFg
by weight, even though the measure portions out powder by volume. I have previously set up the measure to deliver that much powder. I pour the powder down my drop tube into the case. The drop tube settles the powder more consistently in the case than just pouring it in directly from the powder measure.
I place a .030 thick card over the powder and compress it with my compression die so that the top of the card is .470 deep from the mouth of the case. Then I seat my bullet, and cheat a little bit, compressing the powder and card another .030 by seating the bullet. and crimping. Yes, I seat and crimp in one step, I do not have a separate crimp die for 45-70.
Again, that is specific for the bullet I use. You will need to determine your numbers based on the bullet you use, the brand of powder, and the granulation. Hint: different brands of powder weigh different amounts.
Some of your single shot friends will tell you they do not crimp their bullets at all, they only seat the bullet and allow neck tension to hold it in place. That is fine for a single shot rifle, but for a rifle that runs cartridges through a feeding mechanism, like your Marlin, you are going to want to crimp your bullets.
Let's talk bullet lube for a moment. If you are shooting real Black Powder you are going to want a Black Powder compatible bullet lube on your bullets. Standard, modern bullet lubes do not work well with Black Powder, they can cause hard fouling to build up in the bore which destroys accuracy and is difficult to remove. Soft Black Powder compatible bullet lubes, such as SPG, or one of the many home made formulas are best with Black Powder cartridges.
I used to buy my 45-70 bullets from Buffalo Arms. I have quite a good supply, and they don't stock that particular bullet any more anyway. Here is a link to cast bullets that Buffalo Arms sells now. A lot of them are out of stock, but some are in stock. You want a .458 diameter bullet for 45-70. They do not have any 300 grain bullets, but there are a couple of 350 grain bullets you might want to try.
https://www.buffaloarms.com/reloadi...s/cast-lead-bullets/411-459-diameter.html?p=1
Buffalo Arms has a lot of good stuff for Black Powder shooters.
You are probably going to want a blow tube when you get your Sharps. Blow tubes keep the fouling in the bore moist between shots. Moist fouling is better for accuracy than dry, hard fouling. The idea is you put the blow tube in the chamber between shots and blow some slow, full breaths into the tube. The moisture in your breath will help keep the fouling in the bore soft and moist between shots. I made my blow tube with a 45-70 case, some brass tubing and some plastic tubing. You can buy one from Buffalo Arms.
Hope this helps.
