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Posted: 9/18/2026 2:21:15 PM EDT
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Does .375 SOCOM require the barrel extension feed ramps to be paired with an upper receiver with NO M4 feed ramps, similar to .458 SOCOM? If so, does your .375 SOCOM 16" complete upper have blended/polished feed ramps? I assembled my own .458 SOCOM and have troubleshot it to the point where it seems a barrel extension/chamber blending/jobis required but that is beyond my skill level. I figured that the smaller diameter of the .375 would feed better in the AR15 platform than the wide, blunt .458 bullet. Please let me know your recommendations. |
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All my .375S have blended feed ramps so IMO it should be done. But, the bottleneck case may make blending less necessary but if the barrel extension feed ramp has a shelf below the ramp, it’s probably best to blend. It does not matter in the least if you use an upper with M4 feed ramp cuts or not. Most all of my uppers have M4 feed ramp cuts and it makes no difference in feeding, but then again, all my BE feed ramps are blended to the upper. Blending the feed ramp to the barrel extension is not rocket surgery. A Dremel and a fine chainsaw sharpening stone and you can blend the upper to the feed ramp quite easily. Then follow up with a rubber tipped bullet shaped polishing bit and you are done. If you freak out over the bare aluminum, hit it with Aluma-Black and quit worrying about nothing. Who made your problematic.458 barrel and bolt? My guess is it’s not a TROMIX. |
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Thank you for sharing your first hand experience, that assuages my concerns that any blending that is actually required is not a catastrophic project. My .458 SOCOM barrel and bolt are from KAK, not a headspaced pair. Magazines are D&H with the half-moon cutout at the front wall, ammo is 350gr FMJ flat point. It cycles appropriately about 40% of the time after 60 rounds being fired through it. The cartridge tends to have a falure to feed by binding on the top center point of the barrel extension/chamber face. The magazines have about a 90% success rate for feeding after trying Duramags initially but still some get stock on the bottom center of the barrel extenstion area. Another forum reply recommended polishing/light blending of the top extension/chamber face to aid with the stovepipe/type feed error. I am considering that the time/effort/cost of tools and test ammo at this point may be more economic to buy a headspaced .375 SOCOM barrel and bolt from Tromix/Southern Ballistic Research and have a much greater degree of certainty. |
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Can you post a picture of the feed ramp? if not done correctly, that can be the issue. As Big Bore noted, you can fix that yourself with the trusty rotary tool. Also, if the bolt has not been given the proper attention - particularly the extractor and ejector - that can cause issues. A picture of the bolt showing those two can also help us see if there could be a tweak to be done there. And if they were overly aggressive on opening the bolt face, leaving the remaining edge too thin, that can sometimes give some headaches as well. We'll get you sorted. |
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"You got out once. You dip so much as a pinky back into this (ARFCOM) pond... you may well find something reaches out... and drags you back into its depths".
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Keep us updated on the solution OP Can’t say enough good things about my one experience with the Tromix product. The temptation to get some of the copies was hard to resist. In the end, your time and wasted ammo is worth more than any price difference. The 375 socom could be a bit more fun, and versatile than the 458. Every person that tries out the 458 is asking me about getting one! The 375 might offer more variety of loads and a bit longer range. If you ultimately abandon the 458 and get the 375 do yourself a favor and start the project with quality parts. Dumb question. You are using a big bore upper, right? Heres my mutt: Tromix barrel and bolt, Aero big bore upper -blended just a little then polished with the contact surfaces of the extension. NEVER has malfunctioned or FTF, including a few mag dumps, using 325gr. Hornady soft points up to 500gr. solids and a few in between. Attached File Built a few years back, as I recall it has 100% basic carbine stuff in the lower. |
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My money is a jacked up extractor and ejector, maybe the bolt face too but especially the extractor and ejector. Do yourself a favor and order a .458 SOCOM bolt from TROMIX. It will have the proper ejector, extractor, and bolt face. Quick tests 1. Look at the ejector. Is it round all the way around on the front of it? Or has it angles from the 4:00 to 9:00 position? If it looks like a standard 5.56 ejector, then they have not done the ejector correctly. Most times a normal 5.56 looking ejector will not let the .458 case slip up and over the ejector before being seated against the bolt face. That will cause a nose up position of the round and make it hit the top of the chamber on chambering.  2. Slip a round under the extractor and push it back against the bolt face. Slowly turn lose of the round. Does it stick in the bolt face or under the extractor? Another mucked up part. When you turn loose of the round it should fall out easily and be pushed out easily by the ejector.  Go to the TROMIX web site and look at the ejector he makes for the SOCOM. You will see how it differs from a 5.56 ejector. And, if you remove the extractor and put a SOCOM case up under it, is should fall out on its own weight. If it sticks in the extractor, the extractor has not been made correctly. Last, this is how a properly made barrel extension should look. While TROMIX/Teppo Jutsu barrel extensions have evolved over the years, they are all very similar to this one and if yours is vastly different, then it may be the culprit to your problems too, and not much can be done about that short of replacing the BE and that will cost you. Better to just get a TROMIX barrel and bolt and be done with it.  Above images courtesy of TROMIX. As to the rim around the bolt face. Run your fingernail across it. Does it shave off your fingernail? If it does, it is too thin and too sharp. Take some 600 grit wet/dry and buff the edges of the rim to remove the knife edge so it no longer shaves your fingernail. You do NOT want to remove metal, just the knife edge. |
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Beware speaking with a sharp tongue as you are apt to cut your own throat.
My name is John Wick, you killed my puppy, prepare to die.
Beware speaking with a sharp tongue as you are apt to cut your own throat.
My name is John Wick, you killed my puppy, prepare to die.
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Here is another TROMIX barrel extension that he used for a while and it too worked 100%. I cannot remember why he went to the current BE like shown in the first BE picture. NOTICE that the bottom center of the bolt lug is still mostly there. Other BE that look similar have done away with the bottom center lug completely. That is a HUGE NO-NO. Attached File |
Join the N.R.A.
Beware speaking with a sharp tongue as you are apt to cut your own throat.
My name is John Wick, you killed my puppy, prepare to die.
Beware speaking with a sharp tongue as you are apt to cut your own throat.
My name is John Wick, you killed my puppy, prepare to die.
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My daughter's 375 SOCOM, I don't think I have ever had any issues with it feeding Attached File |
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Originally Posted By 7mmStalker: homebaker Your upper receiver looks to have little or no material removed from the center of the upper receiver at the bottom of the bbl. extension (?) Did you put this together, or completed upper bought before daughter custom mods? You are correct. When I put it together I thought I might have to round that portion off and polish it but apparently it doesn't affect the function. In the pic it does kind of look like there is a shelf there but the barrel extension pretty much ends where the mag well comes up into it. Build list: Tromix Barrel + extention Tromix Bolt head on a 'rainbow' guntec bolt carrier Iron City Hatchet receiver set Geissele super 42 with H1 buffer |
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