Howdy
1.285 is the industry standard Maximum length for 45 Colt brass. Brass is usually less than the maximum length. I just measured a random sample of my own 45 Colt brass and it is 1.275 long. That's what it is and there is no reason to fuss with it. The reason a maximum length is set is so the completed rounds will still chamber properly. All reloading manuals list both the maximum brass length and a 'trim to length'. When brass has been fired a bunch of times the pressure tends to squeeze the case wall so that the brass grows in length. If it grows too long, the case mouth will butt up against the chamber throat and prevent the cartridge from seating properly. The trim to length is the length to trim the brass back to, usually .005 or .010 less than the max length. Once brass has been trimmed back, it is reloaded until it exceeds the maximum length again. With the loads we use in Cowboy loads, pressure is usually not high enough to squeeze the brass enough so that it grows at all. All my brass is under max length and I have never had to trim any of it. That's what it is and there is no reason to worry about it.
The industry standard Overall Cartridge Length for 45 Colt is 1.600. This is often abbreviated as either OAL or COAL. Sometimes COL. Again, this is a Maximum length. There is nothing that says ammo has to be that long. The idea behind cartridge OAL is a little bit different than the idea behind case length. This is the length that will allow the ammo to function properly in most firearms. With a revolver, all that is important is that the bullet does not protrude from the face of the chamber and interfere with the rotation of the cylinder. Other than that, if if the round exceeds the Maximum OAL by a bit, it does not matter. A rifle may be a different story. Most rifles will have a 'window' of cartridge length that they operate best with. They almost all operate well with the industry standard Maximum OAL. How short you can load them and still have the rifle operate reliably will depend on the individual rifle, there is no published standard for this, you just have to figure it out for your own rifle. I will tell you that I have an Uberti '73 chambered for 44-40 that actually feeds best when I load my rounds .010 or so over the industry standard Maximum OAL for 44-40.
Most bullets have a crimp groove cast into them. The bullet designer purposely places the crimp groove so that when brass is crimped into the groove the finished round will not exceed the industry Maximum Cartridge OAL.
If you are using a SWC bullet without a crimp groove, I suspect the bullet was designed to be loaded into the 45 ACP round, not the 45 Colt round. Semi-Auto rounds are usually crimped with a taper crimp, not a roll crimp, and the taper crimp does not function properly in a crimp groove. 45 ACP headspaces on the case mouth and the case mouth needs to be partially exposed for this to happen. That's what a taper crimp does. This does not mean you cannot use these bullets, but without a crimp groove your crimp must physically bite into the lead to hold the bullet in place. Otherwise the spring pressure of a rifle magazine spring, or the momentum of heavy recoil can cause the bullet to move in the case. I would not worry so much about what the bullet looks like, regarding how much shoulder is exposed, the important thing is, is there enough lead exposed to allow a good heavy crimp to bite into the bullet.
I have two pieces of advice for you.
First, and most important, whenever you are setting up your dies for the first time, or whenever you readjust them to seat a new type of bullet, ALWAYS make up some dummy rounds without primers or powder. These dummy rounds can than be used to assure they will function properly in your firearms, making sure the bullets do not interfere with the rotation of the cylinder and making sure the rounds feed properly through your rifles. There is no sense making up live rounds only to find out they will not function well in your guns. New reloaders often do not want to sacrifice any of their precious bullets for dummy rounds, but it will save you a lot of headaches in the future if you make up some dummy rounds. You can make them up in a few different OALengths until you find what works best for your guns. Afterwards, save the dummy rounds and label them as to exactly what bullet is in them, and what their OAL is. This will assist you in setting up your seating/crimp die the next time you load that bullet.
Second, frankly, if it wuz me, I would not use those bullets. For revolvers and rifles I always use a bullet that has a crimp groove. It just makes life much simpler. You will get a better crimp if you use a bullet with a crimp groove. The bullet will be mechanically locked in place better in a crimp groove and will have less tendancy to move in the case under magazine spring pressure or heavy recoil. Remember, interior space is very important. If your bullet telescopes further into the case under the combined forces of magazine spring pressure and the jolt the round receives every time the carrier strips a round out of the magazine, your pressure will increase. Using a bullet with a crimp groove will help prevent that from happening, and in addition, the Cartridge OAL will probably be automatically under the Maximum length.
For what it's worth, my 45 Colt rounds loaded with the Big Lube PRS 250 grain bullet are 1.550 in length. I know the guy that designed the J/P 45-200 round, and when he designed it, he had to place the crimp groove so that it resulted in a slightly shorter round. I don't have any rounds loaded up with that bullet right now, but I seem to remember they were something like 1.480 long. I understand the bullet design was changed slightly and the OAL will be a little bit longer with the newer design.