Originally Posted by SteveC99
The best eye opener for me regarding 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.


Along similar lines... I bought my first 7mm Remington Magnum, a new Sendero, a few years ago when there were shortages of many components. The only new brass I could find was PPU, a brand I was not familiar with. As things turned out, I eventually found some new Winchester brass. The PPU brass averaged 14% greater weight than did the Winchester brass; enough weight difference that I had to increase powder charges by about 1.5 grains with the Winchester brass to get the same velocity as I was getting with PPU brass using a 140 grain bullet.

Nothing wrong with the PPU cases, but I don't recall running into a weight disparity that great with any other brass.