Ok, so many reloaders will tell you to stick to the book if you don't want to blow yourself up. I don't want to blow myself up, but I always question everything. About a year ago, I bought 10lbs or more of Superformance powder. I wanted to try it out for 308, 243 and 30.06. It didn't seem to give me any great boost over what I was already using (except the 30.06 but accuracy was crap) so I put it away. I was looking through the load data I had for 300wm and realized that I would probably have to buy some more h1000 or Retumbo to load for this round. After spending about an hour on the internet looking for these powders in stock, I decided to see if something I had could work.
Varget seemed like it might work for the lighter bullets but definitely too fast for the 208gr. It was then that I decided to look up the burn rates for superformance and was pleasantly surprised to find out it was right in between Winchester Surpreme 780 and H4831. These powders also were sort of middle-of-the-range in the Hodgdon Reloading Center so I thought I would give it a try. According to the data I found, Supreme 780 was the same or slightly faster burn rate than Superformance. I decided to start at the bottom of the range and load 5rds for each 1 grain increase. I started at 67gr and ended at 73 grains. I went with the Hodgdon COL which was 3.420" .
Regarding primers, I only had 20 mag primers left so decided to bench them and use CCI #34 for now. I had many others in my stock but those were already loaded up in my priming tool from my last 308 session and I am lazy.
Back at the range, I setup my Chrony which is a Beta Master and prepared to blow up my rifle with this undocumented load.
DISCLAIMER/WARNING FOR NEW RELOADERS: Any load data in this article is for ONE particular rifle (mine). If you try this load in your gun, it may not feed and worse, it may feed but blow up your rifle causing injury or death. Be very carefull when extending your Cartridge Length over the reloading book published values as there can be dangerously huge increases in pressure.
300 Win Mag, 208gr Hornady Amax, PPU once fired neck sized brass with CCI #34 primer. COL 3.420
67gr : STD = 14, Average 2734FPS, LOW=2720FPS, HIGH = 2753FPS
68gr : STD = 11, Average 2766FPS, LOW=2750FPS, HIGH = 2780FPS
69gr : STD = 15, Average 2813FPS, LOW=2790FPS, HIGH = 2834FPS
70gr : STD = 2, Average 2836FPS, LOW=2834FPS, HIGH = 2838FPS
71gr : STD = 7, Average 2917FPS, LOW=2910FPS, HIGH = 2929FPS
72gr : STD = 10, Average 2973FPS, LOW=2955FPS, HIGH = 2973FPS
73gr : STD = ND, Average ND, LOW=ND, HIGH = ND
Things started of great! I was surprised that my starting point was pushing those big pills at over 2700. My target velocity was 2800 so I wouldn't have far to go. There was absolutely no signs of over pressure whatsoever. Accuracy was not great however. She was grouping around 2" @ 100 yards. I was taking about 5 minutes between each set of 5. I probably got the barrel hotter than I should have as I was in a bit of a hurry towards the end.
I started to see signs of pressure at 72gr. The primers were starting to flatten just a bit and you could see the faint markings of the ejector on the brass face. Still no bulging, cratering or sticky bolt so I thought I would press on. The gun was very hot at this point and I felt if I let it cool down, I might be way over pressure for the 73gr load. At this point I believe something went wrong with my chrony as I couldn't get a reading on the next 5. My guess is that they would have been around 3000fps but this was hotter than I wanted or needed. Still no sticky bolt or popped primers and cases looked fine. Just a bit of flattening on the primers and light ejector marks.
I had gotten the data I needed and headed home to clean the gun and inspect the cases & primers more closely before reloading them. Based on the data, I think I am going to try a bigger batch of the 70gr load. Still not sure what these would do with magnum primers but at this point, I really don't need them!