The 458 SOCOM in an AR15 platform has caught my interest.

I put an upper together about 2 years ago and of and on been messing with it. At first, I had feeding or chambering issues, but I think I may have that resolved.

I managed to get a few pieces of SOCOM Starline brass. This brass and loading data calls for large pistol primers. I don't know if std or mag makes any difference. I did notice one exception - Hodgdon on-line load data shows large rifle primers, but I think that's a mistake.

I bought some powder - SBR - SOCOM, which they claim is developed especially for the 458 SOCOM. That's the powder I've been working with so far along with the large std pistol primers and Starline brass. All seems to show that the choices are right.

IMO, the ideal bullet is the Barnes .458 300 gr boattail TTSX. It's rather expensive but the performance is near perfect for the given velocity; accuracy, feeding and effect.

I bought some Hornady 250 gr no lead (all alloy metal) type bullets and they are the bullets I'll develop loads and accuracy test next since they are much less expensive.

IMO, handloading for this cartridge is the best option since factory ammo is too expensive.

So, I've given some background. Now here's my next challenge:

458 SOCOM brass is not available right now. I discovered that Starline has in stock 458 HAM'R brass. In research I find the differences in SOCOM and HAM'R brass is the primer size and the location of the shoulder. The OAL is the same. The HAM'R brass may be a little thicker due to the pressure differences by design.

The HAM"R brass uses the small rifle primer.

The shoulder of the HAM'R brass can easily be set back properly by sizing in 458 SOCOM dies.

The 458 HAM'R brass was delivered today.

I plan on starting loads at the minimum published data for the std SOCOM brass and large pistol primers, but instead using the HAM'R brass and std small rifle primers (not magnum).

Does anyone have any feedback or thoughts about what I've shared so far?

My only issue with going with the hamm'r route is that you wont have any idea if you are over pressuring the rounds for the AR. You are basically stuck with the minium published loads and hope that the thicker brass doest and much pressure. The AR platform is limited in this case by the back thrust on the bolt. From what I have read, this translates to a maximum operation chamber pressure of around 35-37ish PSI. I'm not sure what wilson combat did to the barrel extension and bolt to handle the 458 Hamm'r pressure but I sure wouldn't chase those numbers in a SOCOM. That being said, I dont think what you are doing is necessarily dangerous or unwise (I drilled out a bunch of primer pockets to accept large rifle primers in my 375 SOCOM and that worked fine) but just proceed with a bit of caution.

One can over pressure a 458 SOCOM handload, using the pistol primers.

As I understand it, there are signs such as marks on the case head. I saw that on my last handloads, using SOCOM brass, and plan on reducing the charge to see if that goes away and the action still cycles as should.

Anyway, thanks for the feedback. It's interesting that you used large rifle primers and that was okay.

Just weigh the brass and see if the case capacity is the same. Proceed accordingly.
You will know when your pressure gets too much; first the ejector hole will show up on the brass. Then the locking lugs will shear off. At that point, put a new bolt in it. You will survive.
I use large rifle primers. not mags. not needed.
I was building the 458 when it first came out and was proprietary. I had a reamer made and called it the 11.6 SPC. Starline brass.It's a good round; mags need tweaked. Although now I build mostly 450 Bushmasters. They feed better.

That seems like good info to me, and a bit funny.

"Then the locking lugs will shear off". I figure to avoid that.

The first thing I noticed about the new brass is that it seemed heavy in hand. I haven't weighed for comparison to regular SOCOM brass yet, but I will do that.

You are the second person to say that you use large rifle primers. I figure if that worked out then small rifle primers ought to work too. I don't know which is hotter or even if that matters in working up a load.

Yea, I'm gaining an appreciation for the 450 Bushmaster. I have a Ruger Ranch Rifle so chambered. I haven't tested it yet. It uses small rifle primers, BTW.

I think I'll go and weigh the brass now and get back with you on that.

=================================================

The weight = 177 - 180 gr, for both the SOCOM and HAM'R brass. I weighed three pieces each.

So, there's no practical difference in weight by comparison.

You aren't burning that much or that slow of powder to need mag primers.

MMM,,
My son has shot and hunted with his .458 Socom for a few years nd had no problems at all. It is deadly on Nilgai, shooting through much like a 45-70 does.
He has used only factory ammo though. He still has enough let for several hunts.

Of course it's just a 45-70 in an AR platform.

Well, dpcd, I've read that before. But IMO the 45-70 cartridge is more versatile in several ways.

It's the platform that makes a difference.

Just look at the load data for the 45-70. There are three levels of performance/pressure. A reasonable handloader may safely interpolate all in between with given powders at the three levels. There are many suitable powders and bullet weights.

It may be the most versatile cartridge that has tested and published load data.

Its limitations are of course the rifle it can work in, with the rimmed case.

The pleasure and benefit of the SOCOM is totally about what it can do in the AR15 platform.

I consider it to be somewhere between the 45-70 and the various 45 cal pistol cartridges, even the Casul or 460.

So, I don't expect more from it, the SOCOM, than that, which is enough outside brown bear protection.

I consider the 458 SOCOM on par with the 450 Bushmaster, except maybe the .458 bullets are superior to .452 bullets. At the weight and velocity ranges for both cartridges I doubt there is any discernable difference in performance.

Of course, you are right. I overstated the case. Well aware of how versatile the 45-70 is.

Magine, I found the Speer 300-grain JHP to be a useful and relatively inexpensive alternative to the spendy Barnes, although it is hard to argue with the Barnes bullet's overall performance.

quote:

Originally posted by dpcd:
Of course it's just a 45-70 in an AR platform.

Ah yes, Christine!

The 458 SOCOM will do what the 45-70 can't do - feed in an AR15. Many loads especially the lighter bullets do cross over with 45-70 ballistics, loaded at the mid-level or moderate level, like for a lever action.

The 458 SOCOM is a very satisfying round, IMO. It has thump, and IMO the recoil is not a problem.