I have a .458 SOCOM I started putting together 3 years ago. It has never worked correctly. I have found out that this is not unusual. A lot of unhappy 458 SOCOM owners out there. I hoping you guys can help. Biggest issue is  failure to feed. Here is how its laid out:
- two SBR bolts. One I modified as per a post on here. The other is completely as received.
-  I am not sure who made the barrel It is 16 inch bull barrel .936, says " match grade" on it.
-  gas block is a set screw set MI no (dimples in barrel but seems solid)
-  carbine length gas tube
- barrel extension modified by the gunsmith I bought the barrel from
- milspec carbine buffer, spring and tube
- MAG industries lower
-  Wilson Combat upper ( flat top made specifically for and marked 458 SOCOM )
-   MI sights
-  all Magpul furniture
A beautiful gun which does not work well.

Problem - won't feed and catches spent shell cases in the bolt. Feeds and cycles well manually.

I measured both bolt faces -  one has inside diameter .471, the other .474 as measured by me which I think is pretty accurate.
The feed ramp I have heavily polished. Likewise the chamber. Both are bright and shiny.
I have a variety of mags, some modified, some not. All work about the same. Best seems to be 20 round VietNam era clips with metal followers
I have 2 types of ammo, both approximately 3 years old. Corbon 405 grain flat tipped and SBR 300 grain Barnes.
Questions:
Any known problems with ammo from these manufacturers lots produced in 2011?
Any mag recommendations?
How about bolt face dimensions? One of my SBR bolts is older, one is less than a month old.
Bullets do not drop freely into the chamber. I have sized but not loaded some cases with a new Redding die. They go in/out freely. I am really suspicious of the factory ammo.

I have built several ARs in 5.56 and 300 BLK, all of which work perfectly. I want a different barrel for this rifle but can't find one. Methinks I got into this one too early. I love the concept but with no SAAMI spec and few providers of parts the 458 SOCOM is a no mans land where you pays your money (lots of it) and takes your chances. I am very unhappy. Any help appreciated. Let me know if it would help to post pics.

Standard AR forged upper?  Has the ejection port been opened up for the larger case?
It may fit through during hand cycling, but may bounce off the edge under firing conditions and never leave the extractor.

I had the same problem.  I changed from Magpul magazines to standard steel ones.  Problem solved.  The cartridge has to be presented slightly tilted up in the front.  Slightly adjust the lips on the mag if necessary.  I did not have to touch mine.

Now there is something that I have yet to figure out.  The 325 gr HRN FTX bullets work perfectly with 28.5 gr H110.  I cannot get the bolt to go into battery with any other bullet.  Played with OAL, crimp, sizing, measuring everything two and three times, etc.  Next will to shorten up the brass a little at a time to see if that has an influence.

Bob

Yes. The upper is sold by Wilson Combat and specifically modified for .458 SOCOM

I have tried all the  mags. I found the MAGPUL was about the worst. I am now using standard  Colt labeled military issued 20-shot mags. Some of them I have cut the half moon in but others are stock. I even tried some CMMG stainless followers. Doesn't seem to matter either way. That is why I suspect ammo or the bolt faces.

I should specify that only the upper forging is Wilson Combat. The barrel and bolt are not. The bolt is SBR.

I just talked to a local guy on the range. He said that the Corbon ammo has known problems with case bulging and crimping. He also said that the early SBR ammo was loaded without sizing or trimming of the new Starline brass being used which caused problems in some guns but not in others. Apparently some guy in Texas had a hand in the design effort at Tromix and had recommended a light or no crimp. Of course I don't know this guy from the range so it may be just hot air. In any case I may try to find someone with a bolt gun to try it in and use my buddy's chrono. The new brass I bought had to be heavily sized and trimmed. It was way out of spec. Some was shorter than the recommended trim to length and some was as much as .004 longer. I hope to get some of it loaded soon to see if it works better than the factory stuff.

As an aside, the reason I built this gun is because I have been a lifelong devotee to big bore guns. My main hunting caliber is .45/70 with a Marlin lever action for 150 yards or less and an interarms .458 for longer shots. I found the allure of a .45/70 equivalent in a semi auto  platform too hard to resist! Sorry kids but I am investing your inheritance in guns! You can sell them when I am gone!

Sorry to hear of your frustrations on your .458 SOCOM build.  I purchased a RRA .458-LAR complete rifle in 2007.  It has run like a Swiss watch right out of the box.  I have only used my own reloads as ammunition, and have been very pleased with the results. Like you, I only use milsurp 20 and 30 round M16 magazines.   Soon after buying the rifle, I bought a cartridge gauge from Marty Ter Weem, the man who developed this round.  This has been a great help in reloading.  However they are hard to come by at this time.  Since Marty is currently working overseas, he contracted with SBR to build the parts (including these gauges) for the .458S, but I keep reading they are behind in keeping up with demand.  (By the way, Marty is the “some guy from Texas at Tromix” that you reference in one of your posts.)  

Again, I read that Marty has only contracted with RRA and SBR to build .458 parts and firearms.  Tromix has stopped their production on this rifle some time back.  Only these companies can or could chamber barrels using Marty’s   chamber reamers.  So unless the barrel you have is made by RRA, SBR or Tromix, it will probably have been chambered with a reverse engineered reamer.

You state in your original post that “It has never worked correctly. I have found out that this is not unusual. A lot of unhappy 458 SOCOM owners out there.”  I have not seen this over the past few years.  I hang out here on the AR Variants page as well as the Indiana Forum.  (Back in 2006 the .458 SOCOM became one of a limited number of center rifle cartridges that were made legal for deer hunting.  Prior to this we could only use shotgun slugs, muzzle loading rifles, and certain centerfire handguns.)  I also cruise .458socomforums.com.  I see occasional issues with rifles in this caliber, but not a great number.  2 or 3 years back, RRA seemingly used chamber reamers past their useful life and some guns and upper assemblies were shipped with rough chambers.  These were fixed upon return.  Corbon ammo released a lot of “hot” ammo that sheared locking lugs off some bolts.  RRA still has a warning on Corbon ammo posted on their website.  And, as you say, all factory ammo has been problematic from time to time.  I am sure there were other minor issues.  But for the most part, the guns have run well both for hunters (for deer, hogs, and larger game) and operators in harm’s way for whom the caliber and uppers were originally developed.

Hopefully your handloaded rounds will correct your failure to feed situation.  If it does, I know you will be happy with your rifle.  You might take a look at the threads over on the .458socomforums.com.  There is a lot of useful info there.

+ one on the 458socomforums.  You can get help there, even Tony from Tromix hangs out there from time to time.  There is a ton of info and wisdom IRT the 458.  

I have had my RRA Carbine length upper on top of an M&P15 lower.  No real bells and whistles just a stock rifle.  It has worked flawlessly for 2 years now.  I have run Wilson Combat ammo, SBR, and my own reloads.  I have only had a minor problem with FTF due to dirty powder residue.  Once I cleaned the rifle the same ammo fed and fired just fine.  

The SOCOM has become my favorite rifle.  If is a blast to shoot and those big pills do a number on targets. can't wait till I can try em on a hog.

First of all you need to go to 458SOCOMforums.com and register.  Top post, send email to TonyM and get registered.
Second, your feeding is likely the feed ramp is not cut deep enough and is too shallow.  You should not need to tweak the feed lips but if your BE ramp is not cut correctly, and that is my guess, then tweak the feed lips so the front of the round rides just a hair higher.  Not much is needed.
That should solve your feeding problem unless your bolt face is too small or your ejector is flat faced.  Take your BCG out of your rifle and take a round and insert it into the bolt face under the extractor and depress the ejector.  Let go.  If the round does not flip out immediately then the bolt face is too tight or the rim is too big.  I measured a bunch of my .458S rims and they were .471-.472.
If they hang up the bolt face needs to be enlarged.  
Next look at the ejector.  It should have a bevel on it and not flat across the top.  SBR for some reason has decided to leave off the bevel on the ejector and that causes brass to hang up on feeding.  Not much of a bevel is needed but it is needed.  Look on the socomforums mentioned above so you can see how they should be beveled.
It really is a simple job to do with a pillar file or good stone.
If you need your bolt opened up a hair, contact the bolt maker and they should do it for free.  I know SBR had a problem with too tight a bolt face a couple of years ago.  Or you can contact Tony at TROMIX.  He may open it up for you and he will not charge you an arm or a leg. Also, Thomas at Paladin Machine Shop Service will do it too.  He is also a long time .458S smith.  No web page for Thomas but he can be reached at 803-475-7542.  He is not a fly-by-night .458 SOCOM builder.  He has been doing them with Marty and Tony for well over a decade.

Thanks. The bevel is as deep as it can go.  I thought the 458 socom  forum was closed. I will try it. Thanks again for all the info.

The bevel on the ejector, not the extractor.  From the SBR bolts I have seen there is no bevel at all on the ejector.
Look at the ejector in the below photograph.  The bevel on the ejector is on the left side of it.  If yours is flat all the way across, make it look like the one below.

Formerly known as "some guy from Texas" .... now some stray fool making other parts of the world (un)safe.  Sipping on Bombay Sapphire East with 100 Edge.... enjoying 35°C and 96% humidity....

Anyway.  I spec'ed my bolts at .480 +.002/-0 because as brass gets used it gets nicks in the rim and starts binding.  Listen to BigBore on the ejector.  Also, the barrel is of unknown provenance.  Please post a picture of the feed ramp as it may be part of the challenge.

Final quick fix - polish your chamber.  Shotgun chamber map with Flitz mounted in a cordless drill.  Get it mirror smooth.  Often works wonders.  And use the CorBon to pull projos, dump powder, resize and reload....

Keep us posted.

I had seen the post and pics on the other forum some montss ago and I had rounded the corners on the extractor as recommended however I had not done the ejector as the photo made it look like crap. This is much better. I like it and will get out the Dremel and do my ejector hopefully over the weekend. Thanks for the tip.

Marfty!!!! I read up on the .458 SOCOM and found your very prominent role. Good concept. There seems to be a real tangled web with multiple reamer designs out there. I know that the people at SBR and RRA sell a lot of guns using your authentic reamer but that others (Wilson? , Sterling? ) sell a lot of guns, primarily to Govt. accounts too, I would love to see the 458 SOCOM go mainstream with multiple vendors for ammo, brass and barrels based on a single standard design in SAAMI. I know they all fire the same rounds now but using multiple reamers could cause issue. I will consider it more than a passing phase when the ammo shows up at bass pro shop or even Walmart.

Hey Marty I think we may have met about 4 years ago in Thailand? I was diagnosed with cancer in 2011 and had to retire from my career marketing defense products around the world. Chemo brain is the reason my .458 SOCOM has been "unpolished" these last three years. I am feeling great now and hope to get her shooting right very soon.

Thanks for bringing this wonderful concept to the AR platform and thanks for the tips.

You really need to get over to 458SOCOMFORUMS.com because there is a ton of information that addresses a lot of your comments in your last post.  The .458 SOCOM IS about to go mainstream because it is slated to be SAAMI adopted sometime this summer.  There are not a lot of reamer designs out there, only two that in widespread use,  PTG and the original.  Teppo Jutsu, SBR, RR, TROMIX, and SSK use the originals which works with all in-spec loads with all bullet weights.  Everyone else in the states are using the reverse engineered PTG reamer which has problems with some manufactured ammo.
Once the SOCOM gets SAAMI approval then it would be really stupid if PTG did not correct their reamer specs so everyone one will be on the same page.  At that point the specs will be open sourced.  That's no guarantee that PTG will correct their 'close but no cigar chamber'  but I cannot imagine producing a close copy when it would be just as easy to produce an accurate copy.

I had a lot of problems with mine back in the day (early barrel from Marty) and it was all centered around the extractor.  I finally purchased one of the extractors made for the 45acp guns when they came out and after that seems to be working fine.  I also polished the inside of the bolt face to make sure the the case would tip in and out smoothly.  My chamber is also tight, I recently bought some Wilson rounds and they chamber tight, not a problem with my handloads, just the factory.  Having a SAMii spec should help with this.

Of note, I believe Tromix is going to start producing extractors and bolts, I think there is a thread on the SOCOM forums regarding some beta items.  Also, Harrison at ar15performance.com has his 800-series bolts (for his 270AR and 6mmBR) they have a custom extractor which is for the same size case head as the socom.  His bolts and extensions are interesting in that I think they would be ideal for the socom, even though it is a low pressure round, the extra meat  around the case head would not hurt.

Wow. Thanks TK064. I confess to being out of sync with  the 458 SOCOM forum. I will check out the extractors you referred to. I had modified the extractor on one of my SBR  bolts as per some illustrations on the 458 SOCOM forum but that did not help. I also talked to some people at Sterling and found they use the stock SBR  bolt with great success and do not modify the extractor or ejector pin. Also they grind the barrel extension differently than mine and use a  CNC lathe so the extension is smooth and nice. I cannot find anyone willing to sell me a machined (as opposed to "Dremmeled") extension. To my experience, the few people who are able to find and purchase a barrel have received it without the barrel extension being modified. Wilson and others advertise "kits" with barrels fitted to modified barrel extensions but good luck trying to buy one. I suppose even if I found a modified extension I would not have the tools to properly set the headspace. Its frustrating.

If anyone knows a source of barrels, modified extensions, or high quality brass please let me know. I am wanting a 9" pistol barrel for my next build. If I could get this beautiful gun to work reliably I will probably sell off my .45/70 guns, reloading gear and hundreds of rounds of .45/70 ammo. Need the room in my cabinets and .458 SOCOM is my preferred round as long as its reliable.

TK064 I just ordered a .45 ACP extractor from Olympic Arms. Will let you know how it goes once I get it installed. One of my top priorities for this weekend is to get some 300 Grain Barnes projectiles loaded. I have a few hundred sized, trimmed and primed cases. Will try a variety of loads and see what works best. Do you use an adjustable or switchable gas block on your gun?

Post a picture of the extension "as is" and I can walk you through the process of making it "right" with minimal tools.  Trust me, did it for 10 or so years....

It is a shame that there are rip off reamers out there and hack gunsmiths modifying things that should be left alone . to the op you would be wise to take marty and big bores advise . post a picture of your barrel extention and get a solid answer if that is your problem or not. I bought my rock river 458 socom back in 2007 and had nothing but trouble until I quit using corbon ammo . It has run like a champ ever since . good luck and I hope it works out for you with out having to spend a bunch of money.

Sure thing. I will post one later tonight. You are the authority on this caliber and I appreciate the offer.