458 Socom is likely the most misunderstood caliber that has gained popularity in recent years because it's seemingly so easily interchanged on an AR platform that most of us already have a few of. However, it should be noted that changing parts and pieces on an AR is not like putting together a lego set. Just because the parts and pieces fit together, does not ensure functionality.
As an ammunition manufacturer for a round that's not a SAAMI spec round, we've found that there's a lot of variance in what rifle manufacturers are passing off as acceptable and "within spec", so we dug into it a little further to better understand what's going on out there.
The original developer of the 458 Socom, Teppo Jetsu in combination with Tromix, set the standard. They made the rifle and the cartridge and set the expectations by which it should be made. Tony Rumore, of Tromix was nice enough to spend a LOT of time with me taking me through the history and how we got where we are now with this cartridge.
A Google search will easily take you to the backstory of how Marty of Teppo Jetsu and Tony came together to have Tromix build the original prototype, but the important story here is how it got so messy.
When the original specs were outlined, Tony applied his extensive experience with building 50 AE uppers to making the 458 Socom setup. Every detail was carefully configured to eliminate the risk of feeding problems; from the absence of a chamfer on the bolt face to a tiny bevel on an ejector. The original reamer was made only by Manson Reamers and that became the standard by which the barrel was produced.
For the original ammunition, the cartridge was so new that the brass manufacturer couldn't justify a large batch and the expense to head-stamp it with its true name, and neck it down, so the original casing was incorrectly labeled as a 50 AE and looked like a 50 AE that somehow made it through a little too long. Ammunition manufacturers were responsible for necking it down and bringing it to .458 Socom size.
Once the round and rifle expectations were set and the caliber started to gain momentum, rifles were being manufactured by a few different manufacturers. We'll call them the innovators. The innovators had access to Marty and Tony's plans and were correctly reaming barrels to the expected depth using a Manson Reamer. Not everyone was making bolts and extractors identically, but for the most part, we had a chamber depth expectation that was being met.
Naturally, someone had to follow suit with manufacturing ammunition for the masses. The largest brass manufacturer in the country made a run at necking down the casings themselves, unintentionally producing brass that was grossly out of spec. The head space was excessive to the degree that case separation became a major issue. The shoulder diameter was .004" more than what the original print showed and consequently, anyone making ammunition had a lot of extra sizing on their hands.
To compensate for the excessive head spacing on the next production, the manufacturer made the brass quite long- now each casing needed to be fully resized before loading and the onus was on whoever was making the ammunition to accommodate the rifles they were trying to feed.
Now the speed in which you read this chain of events is in no way reflective of the speed in which they occurred. As brass was being made slightly out of spec, ammo was being made slightly out of spec**. The early adopters that decided to take on manufacturing 458 Socom uppers and barrels now had 3 different sets of specs to choose from: the original Tromix specs (.533"), the excessive headspaced ammo specs (.535), and the overly long specs. In fact, it got so confusing that even Manson Reamers made a Version 2 at .538 to accommodate what was happening with the brass. Other reamer producers made changes to theirs as well. The result was an "out of spec" mess.
Now, as you read this, maybe you have one of the barrels made by an early adopter, someone that came to the Socom manufacturing game as it got messy. You may be wondering, "Now what?!" You're faced with two choices: the first is to go back to the innovators. One of the original guys that know what's what and did it right from the beginning. There are a few, but of course Tromix would be my first recommendation closely followed by Rock River. The second, is to approach your manufacturer and try to figure out what your options are. From what we've experienced, many of the newer manufacturers will help with getting your stuff to the specs intended for the cartridge. There are also a few machinists/gunsmiths that specifically specialize in making 458 Socom right. If you need a recommendation for that, email me at firstname.lastname@example.org and I'll help you find someone qualified.
It's important to note too, that a head-space gauge is not representative of what a loaded cartridge should be. If a reamer manufacturer uses only a head space gauge to manufacture barrels, there's potential for the chamber to be dimensionally incorrect. The diameter, throat and lead isn't being measured by that gauge alone.
The last and most important point to be made here is that at Defender Ammunition Company, we originally made our 458 Socom ammunition to the Socom expectations set by Teppo Jetsu and Tromix. We stood by the innovators and thought that we would be doing them a disservice by running ammo to meet the specs of every barrel manufacturer out there. That said, there is an overwhelming number of variations in the "specs" for 458 Socom on the market at this point. It has become necessary to accommodate the gamut of chambers out there by altering our specs just a bit. While the original ammunition runs phenomenally well in rifles that were made correctly, we're confident that this slight change will not adversely change the round's performance.
As always, we appreciate your business and thank you for taking the time to better understand this wildcat caliber.
**this was long before Defender Ammunition started making Socom.