Tromix .375 SOCOM


Over at, Tony Rumore of Tromix Lead Delivery Systems started a thread showing his new .375 SOCOM round. Cases are formed from 458 SOCOM cases run through a 375 SOCOM sizing die (custom die.)

Rumore reports getting a 200 grain Sierra FP to more than 2,600 fps using 55 grains of AA2520 powder and a 20″ barrel.

It appears Rumore is gauging interest in the new cartridge for the purposes of running a batch of barrels. If you are interested in reading more about the cartridge or seeing more photos, head over to and read the thread.

Richard Johnson

An advocate of gun proliferation zones, Richard is a long time shooter, former cop and internet entrepreneur. Among the many places he calls home is


  • Giolli Joker

    I wonder how this compares to the .375 Reaper…

    • Anonymoose

      More case capacity, for one thing. I wish they’d bring back the Phantom series of cartridges..

      • John Allen Culpepper

        We got that problem solved at Whiskey 3 Precision Systems it’s called the .500 T.K.O. ™ cartridge and the .510 UCMJ ™ cartridge bot use common 338 Lapua mag brass no expensive $5.00 hard to find Jeffrey brass and no neck turning ect. Same to slightly better ballistics as well.

    • John Keene

      It sucks in comparison, 5X more expensive to reload, hard to find cases (remember the cases are “proprietary”, .308 cases of the Reaper can be found at any gun range floor. Not worth it in my opinion.

      • John Allen Culpepper

        Common sense prevails brother!! You get it….lol

    • John Allen Culpepper

      We run about 80 fps slower than the .375 SOCOM. …but we do it where it cost you 3 times less to load for it and have more mag capacity. We run 308 Winchester ballistics with more kinetic energy and do it on the common and reliable AR 15

  • Andrew Hobby

    Cant wait for the .308 SOCOM…


    • pomofo

      Why not the .223 SOCOM? 55 grain bullet at 3300 fps out of a 20″ barrel? Whoo whee!

      • Andrew Hobby

        I’ve begun working on the generation after the .223 socom – the .300 socom super-quiet (.300 SUQ)

        • PlumberofNazareth

          We can even build a light, silenced carbine called the African Weasel designed especially for this round!

  • Vitsaus

    -Obligatory comment about how this is a game changer because it is X better at Y than (fill in the blank other big bore proprietary cartridge created for the M16) and how the poster can’t wait for these to become available on the market for his hog hunting-

    • Ethan

      Niche cartridges have their place too.. its not wrong to be excited about it.

      • Vitsaus

        You’re right… why would god have made them if god created niche cartridges in his own image…. god loves all cartridges. There is nothing wrong … its totally natural to have these feelings, don’t let society tell you its not just because “most” people don’t have those kinds of feelings about niche cartridges. Just because they aren’t “normal” doesn’t mean they should be treated any different.

        • Dan

          Cartridge bigotry aint nobody got time for that

    • David Knuth

      The game’s been changed so often because so many of the new things shart themselves early on XD

  • Dracon1201


    Oh boy, another boutique round that will never take off, and we will never hear of again…

    • Tony Rumore

      That’s what I heard when I made the first .458 SOCOM back in 2001.
      Tony Rumore – Tromix

      • Dracon1201

        Hey, doesn’t mean it can’t happen, but the chances of doing so are so slim. There are other .375s out there anyways. Chances are, this will go nowhere.

  • echelon

    It’s the little guys that aren’t afraid to take risks that many times leads to the inspiration or innovation for the next major breakthrough…

    Although, physics being what it is, we’re kind of at a technology plateau so I guess we gotta bring on the Phased Plasma Rifles at some point to truly jump forward, no?

    • Vitsaus

      The real innovation can only come from materials. I agree fully that ballistics and mechanics are at their peak (past it maybe). Where the future resides is what we can make bullets/propellant/cases from, or what we can make the arms themselves from.


        Simple darts and/or slugs electromagnetically launched from a railgun.
        Just something I’m looking forward to in the coming decades.

  • Hokum

    Does SOCOM (Special Operations Command) utilizes any of these rounds?

  • tony

    Why not just shoot 308 AR-10?
    Granted .375 socom has more energy in an AR platform

    • Anonymoose

      Teppo Jutsu used to have a thing called the .500 Phantom, which was basically an elephant gun cartridge (.500 Jeffery, iirc) shortened to fit in an AR-10 action, with necked-down .375 and .458 versions called .375 and .450 Rhino, respectively. They were even able to use shorter bullets in the .500 Phantom and chamber a regular AR-15 in it, iirc. Guess the concept lost traction or something, since wildcatting is more of a standard AR15, single-shot, and bolt gun thing.

      • Giolli Joker

        Most of the info available on those is on the forum linked in the article.
        AFAIK the .500 Phantom was killed by cost and lack of availability of brass, I think they had a supplier but once this one stopped producing the Phantom, the only alternative was forming from .500 Jeffery, that is really expensive.
        The necked down versions were short lived even because they never reached the design goals.
        I personally find .338 Spectre and .500 Phantom really fascinating.

        • Adam

          Shame as the project ive been working on, i could easily make a few more dies to produce the Phantom brass since it’s 0.5 inch shorter then the case we are toying with,and we are now looking to rebate the rim too standard magnum.

          • Giolli Joker

            Some more details about your projects? 🙂

          • Adam

            Essentially their case is only half an inch shorter and I’m rebating the rim further down to WSM.

        • John Allen Culpepper

          We solve that problem at Whiskey 3 Precision Systems it’s called the .500 T.K.O. ™ cartridge and the .510 UCMJ ™ cartridge bot use common 338 Lapua mag brass no expensive $5.00 hard to find Jeffrey brass and no neck turning ect. Same to slightly better ballistics as well.

          • Adam

            Who’s manufacturing your brass for you?

          • John Allen Culpepper

            We have a couple of small companies converting the brass commercially for us right now. It’s a simple conversion with everything we do….no rebating cases….no neck turning….no neck reaming…..using easily found and common brass.

          • Adam

            Why dont you just get your new case made from scratch, instead of buying Lapua brass, then having to pay someone to modify it? My modified Jeffery case with the rebated rim will cost me $2.25 each based on a run of 10,000. My mate make 338 brass also.. And the sounds of your case, it would be fairly easy to make on the existing dies with a few modifications, With a new head stamp.

          • John Allen Culpepper

            Where are you getting this done for that price and a low volume? Are you in Australia? Last I checked minimums here are 50,000 pieces for new head stamps. Our cartridges are designed for the resourceful shooters that do this stuff at home in their spare time ect. Much like 300 aac is converted like crazy from 223 brass ect. Don’t get me wrong if I could get new head stamps for a decent price I still have to re sell it for a profit to our clients of course and 500 jeffery brass new or a variant of it here in the states is not cheap at all. 338 lapua mag brass is a heck of alot cheaper than 500 jeffery brass

          • Dr Pepper

            Surely your not suggesting theres anything wrong with getting things done in Australia or by Australians to suggest that 10,000 is a run of ammo for anything but a single gun is insulting even to an Australian, let alone for a sale-able product. Perhaps you meant Canada? lol

          • John Allen Culpepper

            No…no….I have lots of friends from Australia mainly that served in the Military and are Long Range shooters. He called his friend “mate” so I asumed he was Australian. Nothing but good things on my end to say about Aussies. Lol

  • Anon E. Mouse


    • FightFireJay

      Because… Reasons. (Same reason why most of use have most of the guns we have anyways… because FUN! and maybe hunting)

  • FightFireJay

    Tier 1?… but what about Level Alpha?

  • Don Ward

    Can’t wait for someone to come out with a 30-30 SOCOM round.

  • Hokum

    Thanks, that’s the answer I was expecting 🙂 So the name is a pure speculation…

    • Cheese_McQueen

      Marketing, not speculation.

  • iksnilol

    Stuff like this is the reason I hate the AR-15 magwell and magazine. Because so many cartridges are neutered to fit into the magwell/mag.