I would appreciate hearing your views on the following:

1. How do you go about selecting a powder that is not listed in a reloading manual?

2. How do you go about selecting a powder for older cartrideges with limited to no published loading data?

Thank you.

you need to have a starting point.
Most powder mfg have a list of recommended cartrages for each of there powders also comes with a burn rate.
Always select a powder that is within the pressure limits for a given volume for that case. a 308 case would hold 50+ grains of water which equates to grains of powder. reduce the load by 15 to 20% and start load developement.
the hotter the powder the more i would reduce the starting load. if the powder is too hot for your case buillet combination you will have a low percentage powder combination.
I try to stay above 75% load density.
Dave

I have done this numerous times.
The key to success and safety, is to use case capacity as your guide.
If you have a cartridge that is similar in capacity to another, look at the powders used in it, and use the start loads for that cartridge.
A good example is that of the 416Ruger, loading data is scarce, but you can safely use the same loading data as the 416RemMag to the letter, velocities are higher with less powder though, showing it is slightly more efficient than the latter.
There is a formula for determining the best powder, which uses expansion ratio as a guide.
Google it, it's to long to post here.

First and foremost I learn it's published burning rate, and compare it's published dat to loads of cartridges I am familiar with. Then I start low and work up ina normal fashion. Some pleasant surprises have found me this way.

one other thing that you can do is contact the powder mfg. most are great to ialk too and out side of there general info they will help a great deal

Cases of similar construction are nice to compare as well as of similar volume.

Some powders go by 2 different names such as H414/Win. 760, etc. If you find a load for one, you've found a load for another.

Some powders, when you've compared them to other cartridges, have a consistent relationship to another powder (i.e., either a few more or a few less grains).

You can also go to stevespages.com and ask Steve, King of Trivia.