If you should not want to dive into the kinds of things listed below, you might try a box or two of 45 Colt BP loads from Republic Metallic Cartridge, Co. (
www.republicmetallic.com). Friends of mine that have used their 45 Colt BP loads in their rifles have reported very little blowback of BP crud into the receiver. They also got POA accuracy for an all-day, 6-stage match. Rifling was clearly visible all the way to the muzzle and there was lube on the muzzle. These are premium loads that perform very nearly like the high quality stuff from the late 1800s. Their ammo is about 22,00 dollars per 50, which is about 14,00 dollars when you subtract cost of brass. It will cost 6,00-10,00 per 50 to reload.
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I sure would not pick 45 Colt to load BP in for use in rifle. The thick walls of 45 Colt cases are difficult to obturate fully at BP pressures, although there are factors that can mitigate that but, it is really hard to acheive the same freedom from blowback as the 44-40 provides.
First factor would be nice tight chambers -- most rifles in 45 Colt don't have them.
Second is use of a 250 grain bullet, probably sized 0,454 or 0,455, preferably pure lead. The 0,455 pure lead, 255 grain bullets Remington sells for reloading are excellent for use with 777 FFg.
Third factor is to use a full case of relatively fast burning BP that does not create much crud -- something like Swiss FFg, maybe even FFFg, 777 FFG, etc.
Forth factor is to use a good two-lube-groove bullet with premium lube, say SPG or Javalina Alox -- not really needed with 777 FFG but is with Swiss. Avoid excessive lube, it just makes a mess unless the case seals fully.
Fifth, crimp tightly.
Finally, use CCI350 (mag primers).
Perhaps anneal the upper 1/2 of the cases now and then.
SOMETIMES, I have been able to greatly reduce blowback of BP fouling by never resizing the cases. This is not a universal solution, especially in a rifle. For one thing, they may not feed well. For the second, they require oversize, soft lead bullets and sometimes soft fiber wads.
You may get by with less than all of the above six factors..
Lars