It's In The Works: .375 Socom for AR-15!

[ROGER4314]

Had some fun with the .300 Blackout cartridge and later with the .458 Socom and developed some loads that were 100% functional, great hunting rounds and all designed to make the AR-15 kick butt!

The latest one is the .375 Socom cartridge and I'm in it neck deep! There is nothing about the .375 Socom in SAAMI specs but that's in the works as I type this.

Reloading dies are scarce but they're coming soon. Load recipes will start being created (by me...snicker) and we'll see what works best.

The part we'll focus on here is testing which of our loads will function with a silencer and if removing the silencer affects rifle operation. When we determine what loads we like, we'll get them tested for SAAMI pressure results.

The .458 Socom is a beast, but the .375 Socom may fill the slightly less artillery oriented niche and be more manageable to shoot.

It's great to be involved in something totally new. We're helping to break new ground, here!

Having fun!

Flash

 

[southtexaspilot]

I have a 45 Raptor and just started my 375 Raptor build. Both are in the ar10 platform. The 45 using a rimless 460 case and custom mags. The 375 raptor will use 308 brass and factory mags. Plan to load it for subsonic suppressed 350gr smk's. It will be interesting to follow your build. What silencer do you plan on using? What length barrel?

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[rp-]

How will those 350smks do at sub speeds? I thought they needed to go really fast

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[southtexaspilot]

http://www.375raptor.com/375RAPTOR/faq/

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[ROGER4314]

It's pretty early in the game to nail down specifics. The first test barrel was 11" long and the suppressors are being built. They are fiddling with barrel gas port size and I don't have the dies, yet.

Neat article on the Raptor cartridge! It says correctly that the .375 Socom is based on a necked down .458 Socom cartridge case. The .458 Socom uses a case with rebated rim and at first glance, it looks like someone made a mistake! It allows the bolt face to remain close to normal like the AR-15/M-4.

https://en.wikipedia.org/wiki/.458_SOCOM

The whole point to this family of cartridges is to make an upper that will mount with two AR-15/M-4 standard pins and to use an AR standard, unmodified magazine. These cartridges put some real "bite" into the AR-15 or military rifles.

It's all pretty exciting! Stay tuned!

Flash

 

[Dawico]

Interesting. A round that actually fills a gap in the caliber range for the AR15.

A need may be a different story but is also usually irrelevant.

Subscribed.

 

[Mikewood]

Sound like a 357 magnum AR15?



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[southtexaspilot]

It's pretty early in the game to nail down specifics. The first test barrel was 11" long and the suppressors are being built. They are fiddling with barrel gas port size and I don't have the dies, yet.

Neat article on the Raptor cartridge. It says correctly that the .375 Socom is based on a necked down .458 Socom cartridge case.

Stay tuned!

Flash

I'm still waiting on reamers. I'll have 3 barrels built in varying lengths. The 45 raptor took me 2 years. I don't expect this one to go any quicker. I've already filed a lower for sbr.

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[ROGER4314]

One of the piggies taken by friend Jim was shot with the .458 Socom. It was a shot from the front and was supposed to be a head shot but at the last instant, her head came up and the round hit in the neck. That .458 bullet went the entire length of the body and poked out the skin at the butt.

That wasn't one of my loads. Hopefully, mine will expand upon impact. Regardless, the .458 Socom is a beast and the upper assembly attaches with two push pins to the Lower with no modifications to the lower or to the magazine.

Flash

 

[rp-]

http://www.375raptor.com/375RAPTOR/faq/

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Great info on the raptor. When you build one I'd be grateful for 1 dummy or loaded round to add to the collection.

Same goes for the 375 socom. I'd love to have one if you feel like making me up a dummy once you get the dies.

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[Mike_from_Texas]

This cartridge interests me. I already have a 458 Socom SBR and can so this would work with my current can.


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[ROGER4314]

Development of the .375 Socom is moving along pretty well, The rifle is here, but no silencer yet. I noticed that the ejection port has been opened up a little oversize.

We received some 200 grain copper bullets, the die set is here. On Monday, we'll select some loads and order the powders we need for them. We selected some alternate bullet weights, too. The die set for .375 Socom is robust, to say the least and it comes with a forming die to make the brass from .458 Socom cases. I put my foot down on that idea. My arthritic elbows are NOT gonna form brass cases!

Strangely, the .375 Socom loads use Large Magnum Pistol Primers like we use in the .458 Socom. It's a mystery to me, but I follow the recipe exactly.

Stay tuned.

Flash

 

[rp-]

Weird. While loading some 460 s&w mag rounds I noticed they used large rifle mag primers.

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[TheDan]

I need a picture...
googling...

Holy hell!

 

[Texas42]

Wow

 

[Mikewood]

Chubby!
Can I see that puppy with a 147 JHP?


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[ROGER4314]

I have the dies at home, now and we ordered some powder, primers and 500 brass cartridges today.

No movement on the actual silencer except the paperwork is in the works.

All of these cartridges are designed to put major teeth into the AR-15 without any rifle lower or magazine modifications.

Flash

 

[ROGER4314]

I got the brass and intended to deburr, size and install the primers in the .375 Socom brass this rainy weekend. Well, that went to shxt!

I buy a lot of brand new brass and in every case, it comes to me fully formed. The Tromix .375 Socom brass uses the .458 Socom parent cartridge and it comes necked down with the shoulder formed BUT headspace is not set. Position of the shoulder sets head space and every other new brass cartridge I've ever bought has headspace already determined in the brass shoulder.

It's a simple matter to set the resizing die up or down to position the shoulder BUT I need the cartridge case gauge to do that correctly. It's not a huge deal, but it will take some time to get the cartridge gauge on hand.

Here are the instructions from Tromix:
" With the dies adjusted to about 1/16" above the shell holder, size a case and check it in the case gauge. If the case doesn't chamber or doesn't drop slightly below flush in the case gauge, you need to lower the die a hair and try again. If your case head is perfectly flush with the top of the gauge , you have the head space set to zero and chambering problems can occur. If your sized case drops deeper than .006" below the top of the case gauge, you will have excessive head space and may have case separation occur in your chamber during firing. Adjust your die up or down accordingly until the case head .003" below the top of the gauge."

Using the barrel chamber is a good clue but how much of the back end of that case should be sticking out of the chamber? Nope.....If we're going to do this right, we need that cartridge case gauge, properly form the case, then continue with our tests.

The silencer is still held up due to paperwork but 1/2 of our tests on the .375 Socom are about getting loads that will function the action without the can installed. That can be accomplished while the silencer is held up for paperwork.

The saga continues...............

Flash

 

[ROGER4314]

Received the cartridge gauge, the powder selections and most of the bullets. Gonna size some of the .375 Socom brass in the next day or so and may churn out some of the rounds, soon. It just takes dogged determination to keep moving forward.

Flash

 

[smittyb]

How about some pics of the sizing/loading process?