Wayne,
Yes, I consistently recommend starting with about a 7% powder reduction when a new lot of any component is used. Exception: some loads using H110 or W296. Check the Hodgdon & Winchester manuals as appropriate. These powders have a high balance point and burn less than consistently at lower pressures.
Alliant is simply reporting the results of testing. Unfortunately, they don't fully report what components were used in the tests that they conducted. But with a twenty year span between results, it is not unreasonable to deduce that much has changed. The only load manual that contained specific data on pressure testing (component lot #'s and equipment used) was A-Square.
One other factor here is that the test procedures for handgun ammunition under SAAMI guidelines were changed, oh, about 6 or 7 years back. There was little effect on the low and middle end loads, but some "hotter" loads using medium to slow burning rate powders have tended to be cut. Why the change in procedure? The electronic pressure measuring systems have taught the industry engineers a lot about what goes on in the field of internal ballistics. While there is still much to learn, it had become clear that some loads were generating forces that were responsible for problems in some very popular handguns made by some "top shelf" manufacturers. Remember, the load manuals have to cover several arms for each cartridge, even when the loads are subdivided by classes. These loads may not be heavier than what is appropriate for the weakest arm in each class in the opinion of the ballistic engineer in charge.
Personally, were I shooting your Ruger SBH, and if I worked up my loads using 240 grain bullets with care to 23 grains of 2400, not noticing any pressure signs such as "sticky" ejection, I wouldn't anticipate mechanical troubles in my revolver. If the cases do eject less than freely, or if you see any other sign of excess pressure stop shooting, and back off your load. On the other hand, a prolonged and steady diet of such "hot" loads in a S&W M29 is a pretty sure invitation to mechanical troubles, despite the changes S&W implemented in '89.
One point to bear in mind: used in quantities beyond its working range for a particular load, a weight of powder/pressure graph for 2400 will show a very sharply rising curve. That is pressures increase very rapidly with the addition of very little more powder to a given load. SBH's have been blown up by floks that thought that they were immune to disaster.
Bob
