The best eye opener for me regrding the 7 mm Rem Mag was Ken Water's Pet Loads from January 1981. He referenced a couple of things that he thought were common to the cartridge that affected it round a lot. This was the first round I loaded for back in 1973, and had me scratching my head for quite some time. I have had several rifles (five if memory serves) and they have all been unique from the others. According to Waters there were (as I saw it) a couple of things that affected it. One he pointed to a wide variation in case capacities of different headstamps of brass, secondly he indicated a wide variation in chamber dimensions, as the critical headspace dimension was the belt, there seemed to be less regard for tolerances at the shoulder. Whether or not any of this still holds true, I don't know, but every time I load for a different 7 mm RM, I use a box of factory ammo and my chronograph as a reference point, along with loading notes and good data sources. So I took from that that if you had a particular 7 RM with an oversize chamber and a case with greater internal dimension than another 7 RM, they might be considered a "wildcat" each to the other.

Steve

Theodore Roosevelt: "Do what you can where you are with what you have"