While some of the things your source says about the differences between the two cartridges are true, I'd be very leery about trying to apply 7mm Weatherby magnum data in loading the 7mm Rem Mag.
Anybody who has messed with enough 7mm magnums has noticed the differences in velocity from barrel to barrel, never mind trying to swap data from one to the other. I would not do it.
Provided however (here it comes
......years ago an old trick put forth by people like John Wooters and Bob Hagel suggested that you could throat a 7 Rem Mag to a 160 gr Nosler Partition with its base seated even with the base of the neck. This gives a substantially longer OAL(and longer throat), than many standard 7 Rem mag factory throats(which themselves vary a great deal even today). It takes a H&H length acton to accommodate these rounds.
W hile this is not exactly freebore, with this OAL and throat to match a 140 gr bullet will have jump to the lands.
I owned and completely shot out several of these barrels,hunted with them out west many times and killed a pie of deer, elk, and antelope with them over the years. And for a long time,never ran a 7 Rem Mag any other way. Back before we had RL 22, I used IMR4831 with 140 gr bullets and 7828 with 160's for velocities from a 24" barrel of 3250-3300 for the 140's, and 3100 for the 160's.
With some powders loads would approach 7mm Weatherby data, but the closest I recall was with H4831 and 160 NPT and BBC's. In that particular Krieger barrel, the rifle simply would not shoot until I maxed it out at 70 gr. for a velocity of 3100 fps. It had a long throat but I was jumping those bullets into the lands.
If you look at the Weatherby data in the Nosler manual you will see that it calls for 70.5 as a max load. There was no ill effect,case life was normal and there was never any outward sign of bad stuff. But then we need to remember that H4831 can be somewhat more forgiving than double based propellants. Incidentally I worked up those loads in mid summer and use the rifle to kill my last bull elk in Wyoming.
It's been said that 7mm Weatherby data is a good place to get started in loading for the 7mm Mashburn, which is a larger case than either the Weatherby or the Remington. But even then you have to be careful as some loads listed for the Weatherby are too hot in my Mashburn rifle.If the data is too hot in the Mashburn, there is simply no way that it should be used in a 7 Rem Mag.
You have to use discretion and understand that every cartridge is a wildcat once you start hand loading for it, and there are many variations in powder lots, bullets,,throats, internal barrel /throat and chamber dimension etc. Any combination of these can pile up to give different results...but generally I would not even try interchanging data between the two cartridges, even if an occasional rifle might come close.
