This is done using a chronograph and reading the pressure signs. Between those two things, you should know when you’re getting into dangerous territory. Aside from that, fork out a little extra $ on QuickLoad or grab a copy of Gordon’s Reloading Tool. Quickload and GRT are particularly useful...
Just from QuickLoad, but in terms of velocity, pressure and case fill, R26 gets the highest velocity for the lowest pressure & case fill by a pretty significant margin on a wide range of cartridges.
Nosler and Barnes both have 4000MR as the most accurate for 168gr. 2800 & 2900 fps respectively. Not sure what range you’re looking at, but that’s a pretty respectable speed.
Yes, been doing reduced loads for 308 and others. H4895 and IMR4895 are both easy to reduce. Just set your minimum at 60% of max, so max is 40, your minimum should be 24. IMR4198 is also good for reduced, and sometimes 3031. My reduced load for the 308 is 168gr TTSX with muzzle velocity right...
I usually set my frier on top of my wooden powder magazine. I know it’s ill advised but when I cook a turkey like that and the house is still standing, somehow it is just more satisfying.
A-Frame is 240, 280, 300.
For hard cast, slug your barrel and find someone over on castboolits to make them for you to the hardness you need and the perfect fit for your bore.