The recommendation that Hodgon gives on that web page for finding the maximum load is for cartridges where there is NO PUBLISHED LOAD DATA. For cartridges where there is reliable published load data from trusted sources such as Hodgdon, Lyman, Speer, Hornady, etc., You should never go above the published maximum. For example, for your 185 Grain bullet (which I assume is a Cast bullet), Hodgdon has no published load. The rule here is to use the data for the NEXT HEAVIER bullet, which in this case is the 200 Grain Lead cast bullet. The published max load for this bullet is 6.5 Grains. This is MAXIMUM. For comparison, for the next lighter bullet in their data is a Cast 180 grain bullet, and it has a max charge of 7.3 Grains. So I would NEVER go over 7.0 grains of powder in an 185 grain cast bullet for a standard 1873 type revolver, and to follow the rule, would actually not want to go above 6.5 grains maximum. The fact that Your loads above 7.0 grains showed signs of excessive pressure is not surprising to me. I am glad you did not shoot the 8.5 grain loads in your Colt. That is almost 31% over maximum. I would hate to see someone ruin a genuine Colt revolver (or any firearm) by using loads that are way over pressure. Remember for fast burning powders such as Trail Boss, the pressures can spike VERY QUICKLY once you start to go over the published maximums. This is not just my opinion, but the rules given by every publisher and from anyone I know of who is a qualified ballistition.
http://www.hodgdonreloading.com/reloading-education/safetyAs a side note, even though Hodgdon says you can use that formula for handgun loads, you will note that they only show examples of modern high pressure rifle cartridges. I would not use this method for the older low pressure cartridges. I would find another powder that has published data for that cartridge.
