The problem with comparing todays published data on the 7mag is,it's been loaded waaaaaaaaaaay down to make the more recent larger 7's look a lot better.My older manuals are right on with max loads and velocities as compared to most of the new ones these days.The 7mag is as good today as it was when it was first produced,only the loadings have been changed.
I don't know that the reason was to make the newer 7's look better. There was the STW and maybe a couple of others, but before a lot of the new-fangled 7's had come out, I read in one of my manuals 10+ yrs ago or more that the reason for the lower velocities at high pressures was due to shorter throat length. There was a push to seat bullets closer to the lands for better accuracy and therefore the chambering was different.
Some of the older models, according to them, had longer throats and the older data reflected that. They attributed some complaints of people being that the rifles used by them to compare data perhaps had significant throat erosion. Accuracy had not been effected appreciably as these are mostly hunting rifles.
Incidentally, my 1964 Lyman manual shows about 3 gns hotter for the 30-06 than the later manuals as well. I can't use that old data in my rifle. Powder lots change and what not. Old manuals become, therefore obsolete.
