Dirty Marlin Ballard

I am tired of cleaning the black powder crud from my old original Marlin Ballard. It is chambered for the 45-100 Ballard Express cartridge and I have shot it for years with some success and fun. Now I'm turning 83 and sick of cleaning it and want to shoot some smokeless powder reduced loads at 100 yds. This cartridge was designed to shoot smaller pistol bullets for more velocity and the groove diameter is .452. I hope to shoot soft cast .454 pistol bullets at 1300 to 1400 fps, and not get the **** kicked out of me for a change, but I am concerned about the loads. I have shot some smokless gentle loads in the past, but due to a fire in my reloading shack (bad lightning storm) I lost all my records and kind of have to start from scratch. The gun has wonderful Tang sights that I can still see quite well, and I don't hunt anymore so I just want to drop a few light loads for entertainment. My hard drive (brain) is full and I don't remember as well as i use to so I would like some opinions on powder, filler use, wads, etc. so I can enjoy the old girl without taking her to the car wash. Thinking about Trail Boss, RX7, or the like...........Any advice or comments will be welcome..............Thanks guys, in advance for you time and help.

Catch

TrailBoss is ideal for light 45/70 loads. I shoot more of that than any other powder.

Another option if you want to reduce fowling, but still like to create a bit of a "fog" when you're shooting your old Marlin Ballard is to duplex load it. It was a very common practice of the Schuetzen riflemen in the late 1890's and early 1900's. A light smokeless "kicker" charge over the primer with the balance of the case filled with black powder didn't appreciably increase the performance or pressures, it just helped to burn away a lot of the black powder powder fouling in both the cases and the bore. They typically used a small charge of bulk Schuetzen rifle smokeless or Dupont bulk smokeless shotgun powder for the "kicker" charge, but today it is common practice to do the same using SR4759 or 5744 or 4227. Since you have a Marlin Ballard it is a much later production rifle and most likely NOT a cast action and should be OK with low pressure entirely smokeless powder charges if you do choose to go that route.
If you are also a member over on the ASSRA site then "marlinguy" is one of the resident Ballard experts and he could definitely advise you on loading your Ballard with smokeless or duplex loads.

(I shoot duplex loads in my Marlin Ballard No. 5 Pacific in .40-90 3" Ballard and we can shoot it all day without cleaning the bore until we are finished shooting.)

https://i.imgur.com/Gi9U4GE.jpg

Catch - 2nd Vote for Trail Boss and duplex reloads with a 'light' crimp

It sounds more like you've got a .44-100 Ballard, as the .452" groove is common for that caliber. I have the same caliber in a #7 Long Range Ballard. When they changed to the .45-100 they opened up the groove to the more common .457" groove diameter. Guessing with this groove diameter your serial number is likely a 3 digit, or low 4 digit, as they changed around 1877 to the larger .45-100 Ballard caliber.
I also shoot nothing but smokeless and the powder Rev. Al mentioned are all pretty good choices for reduced loads in your .44-100. With the slow twist rate of this Ballard, I prefer bullets down around 400 grain for good accuracy.