[kingstrider]

This probably won’t get much attention here but I had a birthday last month and treated myself to a few last parts needed to complete this upper in .458 SOCOM. This will be used primarily for shooting subsonic ammo with a suppressor so the goal was to keep it as short as possible. Major parts include an Aero Precision upper receiver and handguard, a KAK 8” barrel, a SiCo 5/8-24 ASR brake, and a Toolcraft bolt carrier group. After completing the upper I decided to use the red dot on a different gun so mounted a used Leupold 1.5-4x20 FireDot with a Larue QD base instead.

Loading components consist of new Starline brass with Winchester large pistol primers, Remington 405 grain JSPs and Lee 405 grain powder coated cast bullets, and several powders including 1680, Unique and Trail Boss to find what the gun likes. After loading some dummy rounds I found the front of a standard GI magazine scrapes the bullets when feeding. This was fixed by cutting a small circular relief in several magazines. A standard 20 round magazine only holds 7 rounds of .458 SOCOM but should be plenty for my needs.

I did run into a couple of minor issues when loading for the gun. First, the new Starline brass was not sized correctly from the factory so would not seat in a slotted case gauge. This required running the brass through the sizing die to set the shoulder back and reinforces why you should always verify even new brass before loading. The second problem was the seating stem on the Hornady die which damaged the nose on the lead bullets. This was solved by turning a custom seating stem from stainless steel on the lathe. I did not take any photos but you can see the results of the Hornady stem vs my custom stem on the bottom photo.

To date I have shot about 60 rounds of the cast 405 grain bullets using 1680 powder. Subsonic load data is scarce for this powder so I started with a known load and worked my way down. Accuracy at 50 yards was okay but the chronograph data was so erratic that I’m going to try a different powder instead. Regardless, the gun is a lot of fun to shoot and packs a punch even with subsonic loads. For fun here’s a photo of new and old school .45 caliber SBRs.

 

[M1Riflenut]

Nice build. Did you have to open up the ejection port and the edge leading in to the feed ramp?
Built mine a couple years ago on Aero receivers with Tromix barrel and BCG. Went with the 16" lightweight barrel and had the rifle cerakoted OD green. Love this chambering. My next one will be the 375 socom. Got most of the parts for it except the barrel.

 

[kingstrider]

Thanks Dave. I was going to mill one of my spare uppers but bought the 458 upper from Aero which came pre-milled and anodized. This was an easy build, other than the mags I didn't have to modify any of the parts.

 

[Golphin]

I can't believe you can get enough powder in the case to push that big of a bullet. My son and I have built a couple of 300 BO one pistol and one rifle and a number of 5.56's but have not one of those. I really had not heard of it until this post but I am sure my son has as he is much more up to date on the AR's. I really enjoy shooting the 223's though as it is like a hot rod 22 to me. I think if I went big I would go 308 rifle but then again I am not shooting suppressors or subsonic. Just plugging the ears and letting it rip. Looks like fun though.

 

[bryan alder]

Really wanting one of those. My wife keeps saying no. I'll just have to keep asking!

 

[M1Riflenut]

Really wanting one of those. My wife keeps saying no. I'll just have to keep asking!

The beauty of an AR is you can buy the parts a little at a time.......under the radar.😉

 

[flatsneck]

Nice setup! I really love the 458 Socom! its a true monster with full up loads. and subsonic are a hoot to shoot.
congrats on the sweet setup!

 

[GITU1]

Nice build! I only shoot supersonic in mine using 325 gr and 420 gr cast. Has worked well for both deer and hogs.

 

[256WinMag]

Very nice. I really have no need or desire to own one, but I can relate to a time in my past, about 5 decades ago, where I would have preferred this over the modified M2 carbine strapped to my right leg. It was about the same length. It didn't come into play often, but it was comforting to know it was there.

 

[mazer]

Great Build! I have the same issues with the Starline brass, the shoulder is the issue. I have been using 350gr HotCors and that seems to help the situation, I trim the brass back shorter than is recommended. Seems to work for the most part, but still get jams, haven't worked on them in a while, when it cools down a bit, i'll go back to it. I didn't have the issues with the magazines however, might be the shape of the bullet? My rifle does NOT like any of the FTX style bullets, but I attribute a lot of that to the brass.
when it shoots my rifle is MOA all day long, but I have the 16" bbl!

 

[drinva]

I have been fuming to build a 458 for several years. The 458 WILL BE my next build. I'm planning to go full length barrel optimized for hunting purpose. I'm kicking around my parts list still....but I'm gonna!

Thanks for sharing! NICE LOOKING!!!!

DR

 

[10acres]

Very nice

 

[rx7dryver]

I really think these 45 caliber ars are the way to go for a hunting ar. Nice and handy with a 16” barrel makes for a good stalking gun. Carry handle sights would’ve fine for me as they are excellent.

Is there an advantage to the socom over the bushmaster? The straight case bushmaster seems to me that it would be easier to handload.

 

[Moleman]

Very nice! Love the 8" barrel. I've got several big bore AR15's/AR10's that I hunt with the silencerco Hybrid also. Might have to add a SBR tax stamp to the mix after seeing yours.

 

[PoopDeckPappy]

kingstrider,

Very nice. I can tell you are not from California. By the looks she has 8 ways of making you a felon in CA.

Did I miss the barrel twist rate?

I need to move!

 

[mazer]

I really think these 45 caliber ars are the way to go for a hunting ar. Nice and handy with a 16” barrel makes for a good stalking gun. Carry handle sights would’ve fine for me as they are excellent.

Is there an advantage to the socom over the bushmaster? The straight case bushmaster seems to me that it would be easier to handload.

The advantage of the 458SOCOM over the bushmaster is that you can use the same mags and equipment you would use to build a 5.56 AR (Complete lower, and buffer), except of course for the barrel and bolt, I'd check out the TROMIX website for parts and any questions. My 458 is a Rock River ARMs. The Bushmaster (I have this caliber too) is easier to handload, but in an AR frame it needs more specialized equipment including special mags. I CAN tell you that the 450BM in a levergun is outstanding!
Here is a pic of mine, just for fun! I've got it scoped, should really get a new pic of it!
View attachment 9ASJobj.jpg

 

[drinva]

The advantage of the 458SOCOM over the bushmaster is that you can use the same mags and equipment you would use to build a 5.56 AR (Complete lower, and buffer), except of course for the barrel and bolt, I'd check out the TROMIX website for parts and any questions. My 458 is a Rock River ARMs. The Bushmaster (I have this caliber too) is easier to handload, but in an AR frame it needs more specialized equipment including special mags. I CAN tell you that the 450BM in a levergun is outstanding!
Here is a pic of mine, just for fun! I've got it scoped, should really get a new pic of it!
View attachment 725030

I like it!! Nice little setup. What's it weigh? Any idea?

That's one of my worry's with a 458, .....weight. I was wondering what weight range most are in.....

DR

 

[PoopDeckPappy]

I have looked into the 458 SoCom for a few years. A 45-70 semi auto! 300 gr at 2,000 fps and 500 gr subsonic with most everything between.

Again, I need to move!

I am on a California Count Down.

 

[roharmon]

I love the 458 and shoot the NOE 460-405, Lee 457-405 and the Lee 459-405HB with good results, but my favorite is the Lee 459-500. I powdercoat and use Lancer magazines. I have used 296 and Littlegun, but have the best results with IMR 4198.

 

[kingstrider]

Great Build! I have the same issues with the Starline brass, the shoulder is the issue. I have been using 350gr HotCors and that seems to help the situation, I trim the brass back shorter than is recommended. Seems to work for the most part, but still get jams, haven't worked on them in a while, when it cools down a bit, i'll go back to it. I didn't have the issues with the magazines however, might be the shape of the bullet? My rifle does NOT like any of the FTX style bullets, but I attribute a lot of that to the brass.
when it shoots my rifle is MOA all day long, but I have the 16" bbl!

Thanks man! I had some jamming issues at first but the Tromix slotted case gauge really helped me figure out the sizing issue with the brass and where to seat my bullets. Maybe something worth considering if you are still having problems with your loads. Actually the Lee 405s will feed from a GI mag but they were scraping the powder coating and gouging the bullets which are cast from relatively soft range scrap. I have so many mags it was no big deal to modify a few for the build. I don't know if the cheap 8" barrel is capable of MOA accuracy (especially with subs) but as long as I can get golfball size groups at 50 yards the deer won't know the difference.