This is from Hodgdon, makers of Trail Boss
As noted in the powder description section, Trail Boss was designed primarily for reduced loads using lead bullets in pistol cartridges.
However, Trail Boss offers superb versatility in rifle cartridges producing reduced loads using lead or jacketed bullets. These reduced loads make
firing such cartridges as the 300 Winchester Magnum or even the 458 Winchester Magnum pure fun!
Where data is already shown for specific cartridges, never exceed listed maximums. Many original black powder pistol cartridges have capacities
where a full case to the base of the intended bullet, creates charges that exceed maximum pressures allowed by SAAMI. In all these cartridges,
we show data that stays within the SAAMI maximum pressure guidelines.
If you don't see Trail Boss data for your favorite cartridge we have a formula for developing loads for all cartridges and it's simple to follow. This formula may be
used in both rifle and pistol applications:
1) Find where the base of the bullet to be loaded is located in the case and make a mark on the outside of the case at this location.
Then fill the case to that mark with Trail Boss, pour into the scale pan and weigh. This is your maximum load. Pressures will
be below the maximum allowed for this cartridge and perfectly safe to use!
2) Take 70% of this powder charge weight (multiply the maximum load from step 1 by .7), and that is your starting load.
3) Start with this beginning load and work up to your maximum charge, all the while searching for the most accurate reduced load. Once
found, the fun begins
