Camba
What you seeabove is very old data and notice it is for H110.....the old military surplusH110. New H110 and 296 are the same powder made at the same plant. Any variations in new load data for either will simply be due to lot to lotvariations and variations in testing. I'm using Lyman manuals; 3 of them. CBH #3 only lists one load for 296 under the 358156 in the.357Magnum. That is 15.6 gr. CBH #4 and the 49th Edition of the LymanReloading manual do not list 296 but list H110 which is the same powder. They both list 15 - 15.7 gr under the358156. Hodgdon's site, (the maker of both powders), does notlist a cast bullet load for either powder.
I found long ago with rifles in .357, 44 and 45 pistol calibers that the topend handgun loads (magnum level) with PB’dcast bullets are usually not accurate in rifles. The reason is the higher velocities. FB’d aren’t as bad as BB’d and really hardcast FB’d do the best. However, GC’dbullets almost always give the same accuracy potential as jacketed bullets atthe same magnum level velocities. Aquality GC’d cast bullet such as the 358156 cast of COWWs +2% tin or #2 alloy,lubed with a good softer lube like BAC or a NRA 50/50 and sized .359 - .360 andloaded over maximum revolver loads of 2400, 4227, Blue Dot or H110/296 shouldgive very good accuracy, at least what the rifle is capable of. The only caveat should be throat issues asBullshop mentioned. The Lee 158 GC’dcast bullet should also be a good performer as should the RCBS 38-158-SWC. The RCBS heavier 357-180-SIL might also begood but I’m not sure it will fit the magazine of the 77/357 when seated to thecrimp groove(?).
Larry Gibson