pharmertim, thanks for the links! That looks interesting. I suspect they are just using the .499 designation as a designation or unique handle rather than an actual bore diameter. In other words, it's a 50 cal. Now as to the mold I mentioned, it appears to be way too heavy for a standard loading for your rifle. Also, if you were to cast some bullets with it using very hard lead, the weight might get down to around 425 grains,( softer lead weighs more, harder--less).
If you'd like to try some of mine, I'd be happy to send you some. I would not be able to suggest any load data though. As for velocity, I doubt you could get much above 15-1600 fps with a 440 grain lead bullet. Also, there wasn't much detail about the rifle, does it have a normal AR-15 gas system? Shooting lead in the gas system can lead to problems with fouling the gas ports.
I don't see any reason why a standard 50 cal jacketed bullet wouldn't work. Even if the bore of the rifle is actually .499. .001 or one thousandths is nothing when the bullet is being driven by high pressure gases, it will reduce in diameter when entering the rifling.
There's several 300 grain 50 cal jacketed bullets made now. Speer and Hornady both make them intended for the 50 AE. You should be able to load them for your rifle.
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