Just wondering...is your top load compressed and how much? As a rule of thumb, max loads of H110 will about fill the airspace in a straight walled magnum pistol round. If you compress it at all though, you'd better be cautious.
Not necessarily related at all but your model 77 is not a typical .357 (to state the obvious). After not enough initial testing, I once loaded a large batch of .44 Mag with as much W231 as I thought I could get away with . Turns out, it was MORE than I could get away with. Extraction was very hard ("pound them out" hard) in a Redhawk and primers were flattened. My Winchester Trapper would eat them like candy though with absolutely no indication of pressure. Point being, the rifle had very different pressure characteristics than the revolver. If anything, I would have expected the situation to be reversed, the revolver having longer throats and some pressure relief from the cylinder gap. My best guess is that the revolver throats were tighter and that max pressure hits before the bullet reaches the gap. Bottom line, in my case the carbine was running considerably lower pressures with the same ammo.
A similar situation may exist in your rifle.
These were cast loads and keyholed badly from the carbine though and were totally useless. So I pulled several hundred rolled crimped bullets. Lesson learned.
Driving handgun bullets to extreme velocity is definitely fun but can be self-defeating as well, depending on your purpose. They shed that velocity very quickly and many will blow up if you do hit something at hyper velocity. Sometimes that is what you want though.
