Any advice on a 458 SOCOM upper?

[DrHenley]

Update on the SOCOM...

I have a subsonic load with the 410 grain SubX bullet that works. Hodgdon's CFE BLK powder was the magic powder.
And I also have a deer load with the 325 gr FTX that works, using LT-30 Powder that's running about 1550 FPS.
I tried using 300 gr HP bullets but the tip catches on the feed ramp on most mags. It still chambers, but with the tip distorted the accuracy suffers.

Speaking of mags...
30 round 5.56 PMag - I found that crimped, it feeds fine out of an unmodified mag, except for the 300 gr HP.
Uncrimped, the mouth catches on the front wall of the mag. But if I dremel a bevel on the inside of the front wall, it feeds fine...except for the 300 gr HP.

CMMG 10 round mag which is a modified Lancer mag with metal feed lips made for the SOCOM will feed everything, crimped or uncrimped, including the 300 gr HP.

AR-Stoner (Midway's brand) 5 round mag wouldn't feed anything until I did extensive modification on it. Now it feeds everything except the 300 gr HP.