Howdy
Now for the other side of the story.
The 45 Colt cartridge uses a huge, cavernous case, originally designed to hold up to 40 grains of Black Powder. Couple that much powder with a 250 grain bullet and you had a real manstopper, a round that could even put down a runaway horse if needed.
Modern Smokeless powder is much more powerful, pound for pound, than Black Powder and does not take up as much room in the case. Most modern 45 Colt loads using Smokeless only take up less than half of the case volume. That is why Trailboss powder was invented, but that is another story.
One of the problems associated with light loads in 45 Colt is that if enough pressure is not developed by the load, the case will not expand enough in the chamber to fully seal. The result is usually sooty cases caused by 'blow by' as the powder exhaust gasses seek the path of least resistance and blow backwards past the case and out of the chamber.
Also, go too light with your loads and you will start to get inconsistent ignition, which causes inconsistent velocity. That is because most Smokeless powders need to reach an initial pressure of about 5000 psi before they start to burn efficiently. With extremely light loads, that amount of pressure may not be reached, and the powder may burn inconsistently. That is where the huge case, light bullets and light loads can all cause a 'perfect storm' never quite reaching a good consistent pressure.
Very generally speaking, 200 grains is about the limit with light bullets and 45 Colt before pressure problems start becoming evident. Mostly it is just a question of soot on the cases, but I wish I had a dollar for every new Cowboy reloader who is seeking to shoot light recoiling loads with 45 Colt and wants to know why is spent brass is so dirty. Dirty brass and light loads with 45 Colt go hand in hand.
And think about it another way. A very common bullet for 38 Special is the 158 grain semi-wadcutter. If one goes to a 160 grain bullet with 45 Colt, what you are really trying to do is simulate the recoil of a 38 with a 45. Why not just shoot 38s in the first place?
Another choice is loading 45 Schofilelds, or even 45 Cowboy Specials. The Schofield has less case capacity than the 45 Colt and will be less susceptible to pressure problems than 45 Colt. The 45 Cowboy Special was developed specifically for light loads in 45 caliber, it has the same case capacity as the 45 ACP. The downside of these two rounds is the Schofield round may or may not feed well in your rifle because of its shorter Over All Length. The 45 CS round will definitely not feed in a rifle that has not been specifically modified for it.
I know a lot of cowboy shooters want to shoot the grand old 45 Colt because of its legendary connection with the Old West. I also know a lot of cowboy shooters who eventually trades their 45s for 38s because of this. If you go to a major match today, the top shooters are almost all shooting 38s these days, very few are shooting 45s. I was painting targets at the final showdown at a regional yesterday, and I did not see a single 45 on the ground. All 38s.
If you have not bought your guns yet, seriously consider starting with 38s. If you have bought them, do yourself a favor and buy some bullets of different weights and try them. Don't go buying a mold for a bullet you have no experience loading or shooting.
Personally, yeah, I too bought my first revolvers chambered in 45 Colt too. However dirty cases have never bothered me, I only load my 45 Colts with Black Powder and 250 grain bullets.