July 11, 2023
I recently noticed a Lyman ad offering complete packaged sets of tooling for loading several modern sporting rifle (MSR) cartridges. They are offered for .223/5.56, 6.5 Grendel, 6.8 Rem. SPC, .300 AAC Blackout, .224 Valkyrie, and .308 Winchester in three-die sets and .450 Bushmaster, .458 SOCOM, 9mm Luger, .350 Legend, and .50 Beowulf in four-die sets. Each three- or four-die set also includes a shellholder and a cartridge/case gauge. The small base and carbide (9mm only) sizer dies along with a separate taper crimp die ensure reliable chambering and bullet retention during the MSR’s dynamic, self-loading operation. Lyman also publishes an AR reloading manual (now in its second edition) to complement these special reloading tools.
I started using Lyman dies 50 years ago to handload for a .357 Magnum Ruger Blackhawk. Lyman’s 44th-edition handloading manual was the first reloading manual I bought. It provided loading data and instructions for handgun, rifle, shotgun, and blackpowder firearms. Subsequent editions offered only metallic cartridge information because Lyman began publishing stand-alone manuals for shotshell and blackpowder reloading. Two new handbooks were recently added—one specifically for AR cartridges and another for long-range precision shooting.
Let’s take a good look at the .458 SOCOM MSR reloading kit I ordered. It’s a four-die set, and each tool-steel die has a black oxide coating. Lyman’s ad notes the black finish complements your favorite “black rifle.”
The full-length sizer die also decaps the expended primer in the same processing step. Steel sizing dies for bottleneck rifle cartridges require lubricating the cases before sizing and removing the lube after sizing. A small base sizer die is machined to provide a near minimal but in-spec case body diameter to ensure smooth and reliable chambering. The straight-wall 9mm Luger sizer die has a tungsten carbide insert that eliminates the need to apply case lube and then wipe it off. However, this user convenience feature also increases the cost of that MSR die set.
The separate expander die opens the neck diameter so the resized case can precisely and securely position the bullet as it’s seated. Lyman’s special “M” expander plug actually expands the case mouth a few thousandths larger so that the bullet base is easily set in place and aligned properly. The seater die can be adjusted to either only seat the bullet to the desired cartridge overall length or, if desired, apply a roll crimp simultaneously into the bullet cannelure.
MSR die sets include a separate taper crimp die that easily straightens the case-mouth flare formed by the expander plug. It can be adjusted to slightly reduce the case-mouth diameter further to ensure adequate bullet retention. To obtain a uniform crimp, the cartridge cases must be trimmed to the same length and properly deburred after resizing.
The Ammo Checker cartridge/case gauge is an almost required accessory. Compared to a single-shot or bolt-action rifle, the camming force available during MSR operation is substantially reduced. To ensure reliable functioning, a cartridge must be within dimensional specifications. In other words, the case can’t be too large, and the headspace can’t be too long or too short. Proper headspace ensures the round will chamber and the firing pin can strike the primer properly for reliable, consistent ignition.
I routinely drop several resized and trimmed cases into the gauge to check how the case head position is relative to the gauge opening. It should not protrude; it should “feel” just slightly below flush. After I’ve loaded a few rounds, I repeat the ammo check and verify they fit just the same as before. Each round should also easily drop out of the gauge.
In a previous column, I included several .458 SOCOM load recipes using a variety of propellants and bullets, and the performance chart presented with this column includes a few of the best ones plus some additional recipes assembled with the new Lyman MSR die set.
Although I don’t own a suppressor, I safely achieved subsonic velocities with the Speer 400-grain JSP bullet. Those handloads are not listed in the accompanying chart, but I tried two with 14.5 grains of HS-6 powder and 28.5 grains of Accurate 2015 powder. Their average velocities measured with the chronograph’s start screen eight feet from the gun’s muzzle were 1,009 fps and 1,058 fps respectively.
A word of caution is warranted here. When firing subsonic ammo, you must verify each bullet exits the barrel before firing the next round. A bullet stuck in the barrel will cause an extremely hazardous mishap.
All the handloads listed in my chart functioned reliably and delivered excellent and repeatable results downrange. But the various test loads demonstrated significantly different points of impact. Before I take my .458 SOCOM MSR to shoot hogs, I’ll have to sight-in with the exact handload I intend to use.
One final important note: In 2021 the .458 SOCOM was accepted by the CIP (the European version of our SAAMI organization) as a standard cartridge. Multiple companies offer .458 SOCOM ammo; however, Southern Ballistic Research is the primary source of factory-loaded ammunition in the United States.