.458 socom build

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.458 socom build

Postby FJ540 on Tue Dec 13, 2016 6:03 pm

I've had this receiver set in the safe going on a couple years at least, but never had any motivation to build it out until recently. Nothing special; just a TM lower and a blem upper. Filled out with regular parts, and a nitrided BCG from an AIM sale along the way.

When the Black Friday sales started showing up the weekend before Thanksgiving, I'd been talking to a couple friends, and had a couple customers contact me about building a .45 cal muzzle device within the span of maybe 12 hours. The bug bit, and I started fleshing out my .458 socom.

This is the finished rifle, for those of you with ADD:

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458 takes a modified bolt w/special extractor and opened up ejection port, but otherwise uses the same parts as any other AR15. First order of business was to mill out the majority of the material needing removal:

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Then I used a die grinder to blend those edges and chamfer the opening. Teppo Justu's print calls for cutting the bottom of the port much closer to the lower lug than I think is necessary, so I chose to deviate from their design and left more material at the front of the opening. This might cause problems with large heavy sub loads, but I can always open it up more if that's an issue. I also didn't make my opening nearly as wide as their spec, but chamfered the passage instead. The empties fling clear without any impact to the receiver.

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Barrel came shiny, and I didn't want that, so I bead blasted it:

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First range trip, I shot 15 rounds and let a buddy shoot it but he gave up after 2 shots. I lost my good 50yd target at the 45yd line when it ripped off the hanger at Bill's North (not Bill's Baxter North), so I don't have that group to share but it was rather impressive for a 3x tactical scope (was using a Vortex Spitfire 3x prism scope that day). Here's the first two shots out of the gun at 25yds to verify the optic was on paper, and then the 5 round group I shot at 50yds while aiming at the insect without a good reference point (it was a free target, since mine was down range and I didn't feel like buying more for a quick function test session).

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Sorry about the blur, my phone doesn't like the dim firing line lighting.

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All things considered - this being a load ripped off the web and reduced a couple grains just to function check the build; I'm pretty darn happy with the results.

After all, we're flinging these out of an AR15 chassis:

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And here's a comparison between 77gr SMK's and 300gr Nosler BT's

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But my function check did bring up a flaw I had overlooked; the extractor wasn't properly de-horned and was causing the brass to do odd things (like remain inside the upper after a full ejection cycle). After discussing it with the 458 guru's, I took a file to the fangs and brought the gun up North with me for a few more rounds of function testing. This proved all was well with cycling, but temps were low and wind was up so I didn't bother trying to zero the PA scope.

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As the sales kept coming, the deals were ripe and I decided to give Rise Armaments a try with their RA-535 trigger. This thing is almost too nice to hide inside the receiver.

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Likened to a 1911 trigger, this is shorter in both pull and reset than either of mine. It's silly short! I'm curious how this will handle the battering of the 458, and wouldn't be overly surprised if it ends up doubling, but we'll see...

Parts breakdown:

Brownells branded (Satern) 458 socom 16" 1-14 twist barrel/bolt/brake, A1/2 buffer tube kit, black nitride gas tube, low profile gas block
Raptor charging handle FDE
AIM bolt carrier
MI 12" M-loc rail anodized FDE
Magpul PRS stock, MOE+ grip, MOE VFG
Rise RA-535 trigger
Primary Arms ACSS 300blk/x39 ACSS reticle 1-6x24 scope
ADM Recon 30mm mount anodized FDE
KNS anti-rotation pins ceracoted FDE

Once I'm back on the mend after my knee surgery Thursday, I'll be out in the shop cooking up a new device for .45 cal. 8-)
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Re: .458 socom build

Postby BigDog58 on Tue Dec 13, 2016 10:42 pm

Nice setup and that 458 round you had at breakfast last Sat, looked impressive.
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Re: .458 socom build

Postby FJ540 on Tue Dec 13, 2016 11:05 pm

It's basically the same KE as a .308 only in a small frame AR platform. A Lancer 10rd mag holds (4) 458's (if you cut the limiter at the base plate), so that's not any different than most bolt actions out there. When you step into subsonics is where these really come into their own - how about a 550gr sub load? :goofydance:

Part of this build was based on the hope that the HPA becomes law in the next couple years. I never got excited about the 300BLK in a 220gr sub load, but I get goosebumps thinking about chucking slugs at 1050fps.
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Re: .458 socom build

Postby Holland&Holland on Tue Dec 13, 2016 11:05 pm

Did you make a .458 muzzle device then? How does it work?
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Re: .458 socom build

Postby FJ540 on Tue Dec 13, 2016 11:23 pm

This brake is what came with the barrel. I've only had this for a couple weeks and I've been busy with my regular STD production and timber sale up North. Thursday I go under the knife for my second knee surgery of the year, and I plan on trying some variations on older designs (previous prototypes) that I think deserve revisiting when I'm able to get back in the shop early next year (14-21 days :P ).

I'm probably going to break down the upper and rethread the barrel to the more commonly used 5/8-24 instead of the 3/4-28 this was delivered as. I've already confirmed with Machinery's Handbook that the minor diameter is over .625, so I just need to make sure the existing threads aren't too far out of concentricity and turn them off to start fresh with the smaller pitch. While I have it in the 4 jaw, I'll probably move the gas block mating surface back to the block's edge to clean it up too. You can't see it in the pic posted, but in person there's a shadow line where the profile steps down to the muzzle diameter and it's enough to irk my OCD. :)
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Re: .458 socom build

Postby Seismic Sam on Fri Dec 16, 2016 6:50 pm

Gee, that extractor looks just like the one on my Tromix 50AE Sledgehammer.... What a coinkydink....

Considering it was Tromix founder Tony Rumore who did the machining for Marty Ter Weem (who invented the 458 Cartridge) on the original 458 SOCOM design, it's NOT a coinkydink at all - it's on Poipouse!!

As far as the brake on a Tromix, it's a testament to what a really bullheaded guy can accomplish without having the cash for a big 3 axis machine. The holes in the brake are NOT simply drilled into the barrel at a 90 degree angle to the barrel. The holes are slanted DOWNWARD from the outside to the inside!! The only way I can figure he did that is by milling holes straight through the barrel, and then angling the mill down 20 degrees or so and making a 2nd cut.

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Last edited by Seismic Sam on Fri Dec 16, 2016 7:13 pm, edited 1 time in total.
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Re: .458 socom build

Postby FJ540 on Fri Dec 16, 2016 7:11 pm

This is a Satern barrel, and who knows where Brownells sourced the bolt from. It's lifetime warrantied, so it was worth the extra $40 over what a thinner profile barrel of equal quality would've cost with bolt, from Tromix (but I think Tony dropped his price $100 when these came to market, because I seem to recall them being more when I bought it). Satern makes these under the blessing of Marty, so it's supposed to be correct to the original.

No offense to Tromix, but this thing shoots 2x better groups than guys are getting out of his tubes and I haven't done any load development yet. 8-)
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Re: .458 socom build

Postby Squib Joe on Fri Dec 16, 2016 8:01 pm

I really want to see what a SilencerCo Hybrid can will do with one of those
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Re: .458 socom build

Postby FJ540 on Fri Dec 16, 2016 8:14 pm

HPA passes and I'll be having some fun with suppressor design. I built this with the expectation that it might happen in the next 2 sessions. :goofydance:

Muzzle devices too, but I really think this is the best delivery system for subs. Like 300blk on steroids.
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Re: .458 socom build

Postby Seismic Sam on Tue Dec 27, 2016 7:15 pm

Well, I'll be interested in what your varying the type and charge of powder produces as far as accuracy changes. With the Tromix 50 Sledgehammer, you just shot the standard 50 AE load of a 325 grain JHP over 32.5 grains of H110/296 and it was a 1/2" diameter center punch. What powders does the 458 like??
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Re: .458 socom build

Postby FJ540 on Wed Dec 28, 2016 6:37 am

H110 seems to be the reloader favorite over on the socom forums with Lil Gun being a close second for those running 325's. I'm going to burn through the rest of my A1680 just to use it up, and then I'll probably start working on a H110 load. What surprised me was how Trailboss is a favorite for subs. Load data from the major players is still very sparse, despite the cartridge being in circulation for 15 odd years. Lighter 45-70 loads translate very well, so if you're not concerned about crossing that line, there's a lot more options spelled out.

My 10.5" Tromix barrel, bolt, and case gage came today. My lower will be here Friday, and my upper hasn't made it to shipping yet (not sure what the hold up is from DSG). There's also another 2 boxes of goodies coming from Brownells (one from before I decided to do a whole new pistol build, and one after that change); which will result in something drool worthy when it all comes together. :mrgreen: Seriously, this is going to be a sexy bitch. :rock:
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Re: .458 socom build

Postby tator2k on Tue Feb 21, 2017 9:11 am

It's nice to see we now have a local 'expert' with this type of build.

Now I'm ready to start mine!
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Re: .458 socom build

Postby FJ540 on Tue Feb 21, 2017 12:14 pm

There's really nothing to it. .458S cycles with everything I've thrown at it so far. Not like 300BLK where you need certain powders to ensure you have enough gas to run the gun.

A1680 burns clean and gives a good group in this one. I found the opposite with it for 300BLK use and proceeded to use it all up on my first socom loads just to make it go away. Well, now I want more. :lol:

Still need to see what H110 does for groups out of the slug slingers, but that'll happen soon enough.
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Re: .458 socom build

Postby Seismic Sam on Thu Feb 23, 2017 7:12 pm

Threw this in my Tromix 50 along with a Rise Black Fallout trigger, and it's an improved gun, and more fun to shoot. Plus that obnoxious Saturday morning cartoon 'BOINGGGNGGNGG" noise isn't there any more. It's not that you can really hear it over the roar of the gun, but when it's GONE you can tell the difference.

https://www.jprifles.com/buy.php?item=JPSCS2-15H2
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Re: .458 socom build

Postby FJ540 on Thu Feb 23, 2017 10:26 pm

Out of all the AR's I've had, only my Colt made the crunchy sproong sound after the shot.

Use higher quality buffer tubes. ;) There's about .010" difference in ID between the Vltor A5 I just put on a Huldra lower than whatever Adams used (I had to turn down my nylon puck to get it inside the Vltor and it'd slide down the AA as cut from the stick - I'm not using an A5 buffer or rifle spring thus needing the spacer). The other difference is that the OD is larger on the Vltor as well and the CTR lock mechanism isn't really all that beneficial anymore where it wasn't even overly effective on the Adams tube.

I use Vltor receiver extensions almost exclusively because they're one of the companies who uses 7075 instead of the cheaper 6061. They also have a habit of actually fitting nice with collapsible stocks. GD&T is important. ;)
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