Here are the preliminary test results from the first loading of my 720 grain FNGC 458 cast bullet in the .458 Winchester Magnum. One of the forum members volunteered to do the testing. This is not recommended load data. It is only test results from one rifle. These loads may not be safe in other firearms.

Here is his report.

"Today I fired three each of the three loads I wanted to try. Below, I report the raw data, the averages, and the extrapolated muzzle velocities. Speeds were recorded at 15 feet. The MV estimates were done with the Sierra Bullets “Infinity” ballistics program using the Hornady 500 gr RN bullet as a surrogate. The recorded speeds are remarkably consistent.

IMR-3031 51.0 gr
Shot 1 1676
Shot 2 1657
Shot 3 1661
Avg 1665
MV 1680

H4198
Shot 1 1754 51.0 gr
Shot 2 1741
Shot 3 1759
Avg 1751
MV 1765

IMR-4895 51.0 gr
Shot 1 1566
Shot 2 1558
Shot 3 1572
Avg 1565
MV 1580

I have attached a photograph of the heads of the fired cases. They are orientated in rows, top to bottom. As you can see, the primers in the top row (3031) are somewhat flattened, the middle row (4198) are flattened and slightly cratered, and the bottom row (4895) are nicely rounded. Based on this very limited test, I consider 1650 fps MV to be maximum for this bullet in my gun. On my next trial I will decrease the charge of IMR-3031 to 50.0 gr, reduce the charge of H4198 to 48.0 gr, and increase the charge of IMR-4895 to 52.0 gr. I will continue to use Federal Magnum Large Rifle primers. I’ll make a similar report then. It may be a week or two, but I’ll get to it as soon as possible."