I shoot my dad's 1964 M700 in 7mm Mag. Some of the brass is about 40 years old and is still being loaded with the same load of 68 gr of IMR 4350 with a 139 gr Hornady or 140 gr Sierra bullet. A similar load, but not the same, is published in Speer #7, but we use a standard Remington 9 1/2 primer instead of a magnum primer. Speer #7 says a 160 gr bullet can be loaded with 64 gr of IMR 4350 with a magnum primer. The use of magnum primers reduces the amount of powder that can be used safely. There isn't any reason to use a magnum primer with IMR 4350, but if you do, just back the load down 1 gr.

Before anyone brings up the "changes in powder", the same load with new IMR IMR 4350 is within 10 fps of the old DuPont IMR 4350 when shot in the same gun.

It might be a good idea to break down the ammunition you have and reweigh it so it's actually 65 gr.

The 100 yard groups look like this.