Trailboss is made just for this, load data is out there for most any black powder cartridge.
I hear this all the time and it is incorrect.
Trailboss is not made for this. Trailboss is not a Black Powder substitute. It is a Smokeless powder specifically formulated to take up more space than most Smokeless powders. Trailboss is a fast burning Smokeless powder and generates much higher pressure than Black Powder.
Trailboss, as the name implies, was created for Cowboy Action Shooting. Many CAS shooters attempt to load traditional cartridges such as 45 Colt with very light recoil. In doing so, when using traditional Smokeless pistol powders the light loads they created used very small charges of powder. Big, cavernous cases such as 45 Colt do not do well when loaded with a lot of air space inside, it leads to inconsistent ignition and inconsistent velocities. Trailboss has very large, fluffy, donut shaped grains. When loaded properly in large capacity cases they fill up enough of the space to ignite consistently and provide consistent velocity.
Notice how large and fluffy the grains are compared to Unique.
Now..............
Having said all that, I have to ask the OP just how old his 1st Gen Colt is. Colt factory warranteed the Single Action Army for Smokeless powder in 1900. Shortly after that they began marking VP in an upside down triangle on the front left side of the trigger guard. VP stood for Verified Proof and it signified that the steel in the cylinders of those revolvers was strong enough for the pressures generated by Smokeless powder.
This is the Verified Proof marking on a 2nd Gen SAA that shipped in 1973.
This is the Verified Proof marking on a 1st Gen Bisley Colt that shipped in 1909.
Made before 1900? I absolutely would not use Trailboss or any other Smokeless powder in it. I would be comfortable using American Pioneer Powder, which is a true Black Powder substitute, and it does not require special soft bullet lube as real Black Powder does.
Despite what you have probably been hearing for years, Black Powder and BP substitutes do not have to be loaded by volume. It is easy to do a conversion to grains. You just pour out the proper amount of BP, and weigh it. What could be simpler? The proper amount of real BP in any cartridge is that amount that will be slightly compressed by about 1/16" to 1/8" when the bullet is seated. You figure that out and weigh it. What could be simpler? I will caution you though, not all brands of Black Powder weigh the same. So using the above procedure you have to be sure you are always using the same brand and granulation of powder. If you change brands or granulation, just do it again.
I have been loading real Black Powder on my progressive Hornady Lock and Load press for years. I use a special Black Powder measure that will not generate sparks, but I have been doing it for years.
if it burned clean, was easy to clean-up,
Good luck with that. Clean burning does not come along with any Black Powder substitute.
But cleaning up after Black Powder is a lot easier than most think. Despite what you have probably been hearing for years, it does not have to be done immediately or the gun will turn into a pile of rust. Corrosive primers coupled with Black Powder were bad news and caused corrosion quickly. Modern primers are not corrosive and Black Powder fouling itself is far less corrosive than most think. I am not going to tell you how long my guns sometimes sit before being cleaned of BP fouling, but they never get cleaned immediately.
And believe it or not, I use less elbow grease cleaning up after shooting BP than I do using Hoppes #9 after shooting Smokeless. Messy? Yes. Difficult? No.
