Well, as I noted, it could be a lot of different things.
The bullets could have been harder, and given higher pressures, in the 13th edition.
Little changes can make HUGE differences in pressures.
The best thing to do is invest in another loading manual, one that shows 296, such as one of the "One Load" books, which compiles data on a single cartridge from all available sources.
Another good thing to do is to go to the manufacturer's website and download their powder manual. In this case it's
www.winchester.com, I believe.
Their reloading manual can be a little hard to find, but search for it, it's there.
All a loading manual does, though, is to tell you what ONE source found using their components at one point in time. Reloading manuals can't cover all eventualities. That's why you see differences in the recommended loads. And yes, it can be startling to see one book show a recommended load that is significantly higher than another one.
That's why you should always start in the low to middle range for the load given, and slowly work your way up towards full power.