Click on a Frequently Question Below to Link to the Answer.

  1. Who developed the .458 SOCOM? Was it Tromix?
  2. Can I form my own cases? Isn’t it just a necked .50AE?
  3. What does SOCOM stand for?
  4. Where can I buy an upper?
  5. You mentioned the .50 BeowulfTM. Which is better, the .458 SOCOM or the .50 BeowulfTM?
  6. What is the best twist rate?
  7. What is the optimum barrel length?
  8. What is the shortest possible barrel?
  9. What type of velocity can I expect?
  10. What type of accuracy can I expect?
  11. What is the maximum range I can use the .458 SOCOM?
  12. What kind of recoil can I expect?
  13. What lower, stock, other parts can I use?
  14. What are the best or preferred optics?
  15. Where can I buy loaded ammo?
  16. Can I shoot subsonic loads?
  17. How loud are the subsonic loads?
  18. What about putting a suppressor on one of these?
  19. Do I need a muzzle brake? Do you offer one? What about flash hiders?
  20. What about reloading?
  21. I am new to reloading, would this be a good cartridge to learn on?
  22. Where do I get brass, bullets, etc.?
  23. What is the trim length for the brass?
  24. How do I resize the brass?
  25. What bullets can I use?
  26. What about crimping? Bullet set back?
  27. What primers should I use?
  28. What powders should I use?
  29. Where do I get dies?
  30. Which dies are better, CH or Lee?
  31. Can I load these using a Dillon progressive?
  32. Where can I find load data?


  Who developed the .458 SOCOM? Was it Tromix?

The .458 SOCOM was developed by Marty ter Weeme, founder of Teppo Jutsu LLC in 2000. The impetus was an informal ("beer and barbeque") discussion with a senior member of the US special operations community regarding the apparent lack of effectiveness of the 5.56 x 45 cartridge in recent conflict. In particular, the reports from members of Task Force Ranger in Mogadishu, Somalia that multiple shots were required to neutralize members of the opposing force led to the request to develop a new cartridge that would deliver far more energy from short barrels at relatively short distances. After the design was completed, Tony Rumore of Tromix Corp in Broken Arrow, OK was contacted to build the first prototype. Based on the favorable reviews, commercial production was started and the initial rifles were produced by Tromix. Currently, several firms offer rifles or upper assemblies in this caliber, including AR-15s, AK-47s, single shot and bolt action rifles.


Can I form my own cases? Isn’t it just a necked .50AE?

You could form your own brass; however it would be economically unwise. The only case that has the proper base diameter and rim diameter is the .425 Wesley Richards, which runs about $4 a piece. Any other brass will not have the proper rim size, either too large or too small. In a pinch, you could form .458 SOCOM from .50 BeowulfTM but the rim would be smaller. The initial prototype brass bore the .50AE head stamp and this has caused some confusion. The SOCOM case is 1.575" long, the .50AE is 1.290" so therefore, you CANNOT form the SOCOM case from the AE case.


What does SOCOM stand for?

SOCOM refers to Special Operations COMmand, the joint service command based in McDill, FL that governs the various special operations units such as Naval Special Warfare ("SEALs"), Army Special Forces ("Green Berets") and Air Force Special Operations. The cartridge was given this name based on the original impetus from special operations mentioned above as well as the fact that a similar cartridge saw limited use in Vietnam with special operations as well.


Where can I buy an upper?

At the time this FAQ was written, uppers can be purchased from the following sources:

Teppo Jutsu LLC –

Tromix Corp –

SSK Industries –

Rock River Arms – – expected 4th quarter 2005

Castle Arms –

In addition, there are a number of other companies that can supply uppers; however, they use barrels and bolt supplied by Teppo Jutsu LLC under licensing agreements.


You mentioned the .50 BeowulfTM. Which is better, the .458 SOCOM or the .50 BeowulfTM?

This is one of those debates that neither side wins. Both cartridges are very similar, yet they are quite different. We had access to some of the information on the predecessor of the .50 BeowulfTM when we designed the .458 SOCOM. We designed it the way we did for very specific reasons. I admit I cannot be impartial, but I will give as honest a comparison of the two as I can:


Rim size – the SOCOM rim is the same as the .308 Winchester (7.62 x 51), the Beowulf rim is the same as the 7.62 x 39 M43 cartridge used in the AK-47. The B rim is easier in that you can use existing bolts for the AR. The S rim is easier in that there are hundreds of thousands of (old) bolt action rifles that use this same rim and that could be retrofitted to the SOCOM (all the old Mauser rifles ….)

Case length – as mentioned earlier, the B is 4mm longer than the S. A lot of this extra room is taken up by the body of the bullet anyway, so it does not gain you that much.

Headspace – the B uses the case mouth, the S the shoulder. There are those that feel using the shoulder offers inherent greater accuracy potential, but both rounds are capable of just about the same accuracy. Both are intended to be used at the same maximum range as well, so it really does not matter much.

Bullet selection – this is where the S has the B beat, hands down, due to large variety of .458 bullets compared to the .500. But with the advent of the .500 S&W, the B is starting to catch up.

Cost/Selection – Before Rock River got into the game, the S uppers were all custom jobs whereas the B uppers were more "semi-bulk". The S uppers are available in just about any configuration you can imagine, but that comes with a price tag. The B uppers come in a certain number of configurations but with a lower cost and they might be a little easier to get (again, before Rock River took up the .458 that is)

Power – Let’s be honest. The difference between a .458" bullet and a .500" bullet is a whopping 0.042" or a hair under 3/64". If you hit anything with either, it will be hurting or dead. That 0.042" won’t matter a bit. Both have just about the same muzzle velocity so just about the same power. The B has a little more room for powder and with the slightly larger diameter bullet will edge out the S. But the S has bullets with much better BC available so it should out perform the B at distance.

So as you can see, the difference is really not that big. A lot of it depends on personal preferences, or perhaps what your budget is or whether you already reload or similar considerations. You can’t go wrong with either.


What is the best twist rate?

One of the reasons .458 was chosen was to allow the use of the commercially available heavy bullets (500 and 600 grains). To stabilize these at subsonic velocities, a relatively fast twist is needed. If you plan on shooting mostly light bullets (250-400) you can get away with slightly slower twist and the slower twist MAY stabilize the 600-grain bullets but likely won’t. Basic guideline is as follows:

Lighter bullets (250-400 grain) – 1 in 18 twist

Heavier bullets (500 and 600 grain) – 1 in 14 twist

What is the optimum barrel length?

The cartridge is intended as a short range "brush buster". As such, we feel the optimal length is about 16", as a compromise between handling and velocity. Longer barrels will NOT offer substantially more velocity due to the fact that relatively little powder is available and relatively fast burning powders are used. As a matter of fact, the factory loaded 600-grain subsonic load is designed to achieve complete powder burn in a 9.5" barrel. Most of the uppers that have been built have featured 16" barrels, with the second most popular length being 20", followed by 10.5" for SBRs/pistols.


What is the shortest possible barrel?

The typical short barrel upper will have a 10.5" barrel; however we have managed to make an upper function with a 7.5" barrel. You can’t go much shorter than that…


What type of velocity can I expect?

Velocity will vary from rifle to rifle and obviously also depend on the bullet that is being loaded. However, some of the typical velocities from a 16" barreled upper are as follows:

300 grain bullet – 1800 to 2000 fps (higher has been recorded)

400 grain bullet – 1600 to 1800 fps

500 grain bullet – 980 to 1300 fps

600 grain bullet – 1000 fps

What type of accuracy can I expect?

As with velocity, accuracy will vary from rifle to rifle. The cartridge, however, is capable of quite respectable accuracy. With hand loads, low power optics and the shooter doing his job, groups as low as 0.5" (yes, true 0.5") have been recorded. We typically tell folks that 1.0" groups at 100 yards are the norm for the 300-grain JHP load. The 500-grain subsonic load does not appear to be as accurate but it was never meant for ranges beyond maybe 50 yards.


What is the maximum range I can use the .458 SOCOM?

The cartridge was intended for short range work, either in dense brush or otherwise in urban theaters for LEO/MIL applications. As such, after 125-150 yards, the bullets tend to drop off VERY rapidly and we tell folks to consider it a 100-150 yard cartridge. Accomplished shooters can shoot the cartridge accurately at much greater distances, just like the .45-70 was used to decimate the American bison population at 1000 yards.


What kind of recoil can I expect?

Recoil is subjective, however, most of the folks who have shot it tend to use the comparison to either a 20- or 12-gauge shot gun. The 400-grain loads seem to have the most unpleasant recoil impulse, the 300-grain does not appear that bad nor does the 500- and 600-grain subsonic load. I have shot it in a 10.5" SBR on full auto with 300-gr. JHP loads and found it not that hard to handle. From the bench my .308 has seemed to kick worse. See the next section about some pointers.


What lower, stock, other parts can I use?

The .458 SOCOM was designed to fit any mil-spec lower. Thus, any of the lowers out there that meet mil-spec should readily accept the .458. No modifications should be needed to your lower and no negative effects to the lowers have been reported. Based on customer reports, the following aftermarket modifications can help reduce any felt recoil and make your shooting experience a more enjoyable one:

Stock – the standard A2 stock has a butt plate that becomes a "meat grinder" with the .458 SOCOM. The most popular stock tends to be the ACE Ltd Skeleton stock with the thick rubber recoil pad. Collapsible/telescoping stocks should be used with caution; we have received reports of stocks failing and auto-collapsing.

Buffer Spring – While the standard spring will work, a lot of shooters prefer a spring with higher spring constant such as the MGI or Wolff

Buffer – Again, the standard buffer will work but the MGI Recoil/Rate Reducing buffer is a popular item among big bore AR shooters

Magazines – the .458 SOCOM was designed to work with any GI/Mil Spec magazine. We have not heard of any particular type or brand of magazine that did not function. Magazine capacities for the different size magazines are as follows:

10 rounds of .223 – 3 rounds of .458 SOCOM

20 rounds of .223 – 7 rounds of .458 SOCOM

30 rounds of .223 – 10 rounds of .458 SOCOM (have heard 12)

40 rounds of .223 – 13 rounds of .458 SOCOM (have heard 15)

The MWG 90-round .223 drum can hold as many as 33-36 rounds of .458 SOCOM which makes for some formidable firepower. The BETA mag WILL NOT WORK with the SOCOM.


What are the best or preferred optics?

Which is better, Ford, Chevy or Dodge? Because of the recoil, the preferred optic will have longer eye relief than typical. Lower power scopes such as those originally intended for use with a shotgun are popular, however, the vast majority of shooters use either the Aim Point or the EOTech as these seem particularly well suited to the type of shooting done with the .458 SOCOM.


Where can I buy loaded ammo?

Right now, only CorBon offers loaded ammunition, specifically the 300-grain Jacketed Hollow Point, the 400-grain Barnes Round Nose SOLID and the 600-grain Barnes Original SUBSONIC. We are working with some other companies to get them to load the cartridge as well.


Can I shoot subsonic loads?

Considering this was part of the original design intent, the answer is a resounding YES. Both the 500- and 600-grain subsonic load has proven quite popular and will function without issue through the uppers.


How loud are the subsonic loads?

While not as loud as the 300-gr high velocity load, they are still not quiet enough to forego ear protection.


What about putting a suppressor on one of these?

Several uppers have been fitted with suppressors, either muzzle mounted or semi-integral versions. Different brands have been reported, such as SRT and GemTech, as well as Form 1 versions built by qualified individuals. With the 500- and 600-grain subsonic load they tend to make for a very nice and relatively quiet package. Suppressing a low pressure large bore cartridge has its challenges, and Hollywood has created a false impression of how quiet a suppressed rifle typically will be. These uppers are not like you see in the movies and a lot of the noise is from the action cycling. If you want the ultimate in suppressed .458 SOCOM, the Remington 700 Etronix version with semi-integral suppressor would have to be it. Other calibers are far more suited to suppressing but the SOCOM is no slouch. Remember that the 11.63 x 33 was used in suppressed bolt guns in Vietnam ….


Do I need a muzzle brake? Do you offer one? What about flash hiders?

This depends on how recoil sensitive you are. ANY benefit in terms of recoil will come at the cost of increased noise to the shooter and surroundings. Because of the large bore and relatively low pressure, most muzzle brakes will not be quite as effective with the .458 SOCOM as they might be with a cartridge like the .22-250. We do offer different versions and some folks report that they make a tremendous difference. A lot of it depends on the shooters preference but the more popular version is the Shrewd brand. We also offer a number of different flash hiders, including an A1 birdcage style made by Tromix and a custom-made Smith Enterprises Inc Vortex.


What about reloading?

Because loaded ammo was scarce for a while, the .458 SOCOM with its wide range of bullets available seems to have found a loyal home with the folks that (like to) reload. All the components are available as is load data so reloading is not an issue. Folks have reported as many as 9 reloads on a single case, making it economically attractive for those already set up to do so. With the wide array of .458 bullets available, (re)loading your own ammunition allows you to tailor a load both to your needs and your gun, which means you can work on getting the utmost in terms of accuracy or velocity out of your particular rifle. Some guys really like their pet loads for hunting, while others just like the fact that reloading can drastically reduce the cost of plinking with the SOCOM.


I am new to reloading, would this be a good cartridge to learn on?

To be honest, the SOCOM is relatively new in the world of firearms compared to such rounds as the .30-06, the .45-70 and many others. It would probably not be the best one to learn on, as it has a few idiosyncrasies, but if you like a challenge….


Where do I get brass, bullets, etc.?

The brass is made by Starline and can be bought straight from them or else through the larger reloading specialty outlets like Midway and Graff and Sons. Just about ANY of the .458 diameter bullets out there will work, and these are readily available at most gun stores that offer reloading components.


What is the trim length for the brass?

The official length is 1.575" but you can go as "short" as 1.570".


How do I resize the brass?

More important than trim length is shoulder set back as this cartridge head spaces on the shoulder. Experienced reloaders will know what this means, but for those that do not – you have to set up your dies such that when you full length size the brass after firing, you do not push the shoulder back down the case. If you were to do so, the case would still chamber, but likely FAIL upon firing. Not a huge issue, just a pain. I have had several do this, before I got my dies dialed in properly. Sometimes the shell holder can make al the difference needed …. I run my dies all the way down to where the fully contact the shell holder and this works for me but again; there are variances in shell holder thickness which can cause problems.


What bullets can I use?

As stated above, just about any .458 diameter bullet, ranging from 250 grains to 600 grains is what we have found out there. Cast lead could be used, but we would recommend limiting the number of cast lead bullets as the lead may foul the gas system. Seating depth can be a bit of a challenge with some of the heavier bullets. NOTE that the crimping groove on many .458 caliber bullets was designed with a totally different cartridge in mind (typically .45-70 or .458 Win Mag). Therefore, the crimping groove will likely NOT line up with the case mouth when seating to an overall length that fits in the magazine (or chambers, there are some bullets that need to be seated deeper due to their profile, such as the 300-grain SinterFire frangible and the 400-grain Speer FN)


What about crimping? Bullet set back?

Crimping is a topic of quite some debate. Both the CH dies and Lee dies allow you to crimp. Typically crimping is recommended to prevent set back of the bullet due to recoil or during the feeding process. However, several shooters report no issue when not crimping and one accomplished reloader/shooter reported a decline in accuracy when crimping. I tend to put a light crimp on my loaded rounds with my CH dies and have not encountered an issue … yet.


What primers should I use?

The cartridge case uses the large pistol primer pocket and we recommend the CCI350 or the WLP primers. DO NOT use rifle primers as the primer pocket is not deep enough to seat them property which could lead to a very dangerous situation.


What powders should I use?

With a relatively small powder volume and low pressure, the faster rifle powders tend to be the more popular and effective. Typical powders include Hodgdon H110, Winchester Win296, Norma N200, Alliant Reloder7, IMR4198 and VVN110. We have also been hearing that Hodgdon Lil’ Gun is producing great results but my personal experience has been that Reloder7 is just about the most forgiving and versatile for the SOCOM and I feel it probably is the best choice. Your mileage may vary …


Where do I get dies?

The first set of dies was made by CH Tool and Die ( and they carry them. Lee also has the dies, but they are down to their last few sets….. If you ask us, we can work with you if you want a different brand like Redding or RCBS.


Which dies are better, CH or Lee?

Both dies have their pluses and their minuses. Another Ford versus Chevy debate some would say. There are some differences; I’ll try to highlight the obvious ones.

CH – The CH dies come as a two-die set with no shell holder. I like my CH dies, but customers have reported that the surface finish was rough, leaving the brass appearing scratched. It does not affect the function of the brass but might be less than ideal. The die set does not include a belling die which never bothered me but can make seating flat base bullets more challenging. The seater plug is designed for use with the 300-gr. Spitzer bullet and will not do the tip of the 300-gr. JHP bullets any favors. Having another seater plug such as one for the 44 Magnum can be a plus. The seater dies also serves to put a taper crimp on the case during the top of the stroke.

Lee – the Lee set does have a belling die as well as a separate crimp die. Again, seater plug issues, as the one furnished is too short for the 300-gr. JHP bullets. Using one from a 44 Magnum die set tends to solve this. The die set also comes with the wrong shell holder for some strange reason …. I do not like the decapper set up on the Lee dies but that is a personal preference.

Can I load these using a Dillon progressive?

You sure can, but it requires a few tricks. You need the shell plate for the .45 ACP and the powder funnel for that one as well. Make sure the dies allow full travel of the ram as that was found to be a problem in one case. The fine folks at Dillon can help you with specifics; I still plod along with my trusty Rock Chucker …


Where can I find load data?

Right now, the best place is to Email us at however we hope to post it on our website soon.


I think this covers just about everything, if I missed anything let me know


Marty ter Weeme
Founder, Teppo Jutsu LLC
Developer of the .458 SOCOM


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Last modified: June 1, 2011