Any advice on a 458 SOCOM upper?

[DrHenley]

I guess it is waaaaay past time for an update on this.
Since neither Hornady nor Hodgdon was much help on load development (at least Hodgdon tried) it has taken many months to come up with a load that meets my design criteria. Complicating things is the fact that I let my range membership lapse, so I have to drive an hour to a public range, or wait until I get to my land to test the loads.

First to answer the question about the Ludex brass catcher after using it a few times...IT WORKS GREAT!

I am shooting Hornady 410 grain SubX bullets, ostensibly designed for subsonic loads. However Hornady acts like they don't know that it is for subsonic loads and would only say that there aren't any suitable powders.

I've been running simulated loads with QuickLoad and with Gordon's Reloading Tool, but for a while the real world results bore no resemblance to the simulations. I finally figured out how to tweak the parameters of Gordon's to make my actual velocity match the simulated velocity, and it came down to three candidate powders.

But before I go any farther, let me list my design criteria:

1080 fps muzzle velocity
Comfortable margin of error on max pressure. (35K is max for the SOCOM)
<=3000 PSI muzzle pressure
Enough port pressure to reliably work the action.
>75% Load density
100% burned powder (preferably before it reaches the gas port)
Easily obtainable powder, or powder that I already have
Under 2 MOA

The final three powders were CFE BLK, IMR 4227, and H110. After firing a load with each that I knew was a bit higher than my goal velocity, CFE BLK came out on top with an honorable mention to IMR 4227.
One thing IMR 4227 has going for it is that I have a lot of it. But unfortunately, after inspecting the bore after shooting the 4227 load, I could see some unburned powder kernels. Not a lot, but some.
In my earlier loads I had a LOT of unburned powder, which got into the action. Also, since this is intended to be a suppressed load, I don't want unburned powder going into the suppressor.

Here is the Gordon's simulation for the final load. The semi final load had a velocity of 1111 fps, so it only took a small tweak. >90% of the powder is burned before the bullet reaches the gas port. 100% of the powder is burned at less than 10". I have five rounds loaded up with this final load, and I'm just waiting to get to the range to confirm it and see what kind of accuracy it has.

[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.