I shot my new 458 SOCOM today. I do not have a .875 gas block or a carbine length gas tube so I shot this in manual mode.
I have ordered a .936 gas block since a .875 was not available and a carbine length gas tube.
I took the side charging upper from my 6.5 Grendel since the ejection port was already large enough to eject the huge 458 SOCOM cartridge. The lower is an 80% I milled out on a drill press.
I loaded ten .452 200gr swc. I had to push the necks into a 45 ACP carbide die to get enough neck tension but it worked.
9gr of Red Dot for a plinking load.
I also loaded ten .458 350gr copper plated bullets the normal way. 7gr of Red Dot.
The Lee dies have a mouth expanding die to ease bullet insertion.
I had some trouble getting it adjusted so I just used my Lee universal mouth expanding die instead which worked well.
The .452 rounds were used for sight in at about 12 yards.
Then I fired the 350gr bullets and got the two groups below.
All the fired cartridges ejected very easily with just hand pressure.
The unfired 350gr cartridges required mortaring to eject them when I was trying to clear an incomplete chambering.
During this time I had a persistent problem shown below. The base of the bullet popped out of the P-mag and was trapped above the ejector. I put the case into the chamber and pulled the bolt back slightly each time and let it slam home. I need to remove the ejector and taper the edges to stop this.
One time when I let the bolt fly into a chambered cartridge I had my first slam fire. It make quite a crater in the ground.
I grabbed a handful of dirt and the bullet came out. It showed good expansion. I am glad I did not slam the bolt home at home or I would have had quite a hole in my floor. I will remember this for the future. These loads were very mild; sort of like light target loads in a 45 ACP pistol but fired in a rifle. The expansion in a full power load should be quite impressive.
Edited by bj139, Apr. 10 2018 - 08:48 PM.