Magazine Math - 458 SOCOM vs 5.56 NATO

[Scorpio64 5,155]

Kinda curious to know how this works.

458 SOCOM uses standard M4 mags.  A mag that holds twenty rounds of 5.56 holds just seven rounds of 458.  A standard capacity M4 mag holds thirty rounds of 5.56, and just ten rounds 458 SOCOM.

So, how does one legally possess a ten round 458 SOCOM mag in the glorious democratic people's republic of New Jersey?

[Displaced Texan 11,748]

I seem to remember some mags (PMags maybe?!) having a follower marked .458 Socom.

 

Think NJ will buy it?

[Krdshrk 3,877]

"Large capacity ammunition magazine" means a box, drum, tube or other container which is capable of holding more than 10 rounds of ammunition to be fed continuously and directly therefrom into a semi-automatic firearm.

With a .458 SOCOM follower, can it feed .223/5.56?  Continuously?

 

[Displaced Texan 11,748]

Here’s a couple 
 

 

https://www.calegalmags.com/458-SOCOM-Magazine-Follower-USGI_p_1397.html
 

https://tromix.com/product/center-feed-followers-for-lancer-mags/

https://www.dark-storm.com/parts/magazines/ar-15-magazines/magpul-pmag-gen-m3-458-socom-10-rnd-magazine-black/

 

[JohnnyB 4,325]

12 minutes ago, Krdshrk said:

With a .458 SOCOM follower, can it feed .223/5.56?  Continuously?

From a quick Google search, the answer is yes!  The .458 was designed to use a standard M4 mag in .223/5.56.

[Krdshrk 3,877]

27 minutes ago, Displaced Texan said:

Here’s a couple 
 

 

https://www.calegalmags.com/458-SOCOM-Magazine-Follower-USGI_p_1397.html
 

https://tromix.com/product/center-feed-followers-for-lancer-mags/

https://www.dark-storm.com/parts/magazines/ar-15-magazines/magpul-pmag-gen-m3-458-socom-10-rnd-magazine-black/

 

If the followers are like these and will not hold any smaller rounds (.223/5.56) then you're fine.  

If can hold/feed .223/5.56 CONTINUOUSLY you'll have a problem.  

[Scorpio64 5,155]

1 hour ago, Krdshrk said:

If the followers are like these and will not hold any smaller rounds

458 SOCOM was designed/intended to run through a standard AR-15 mag.  Some unofficial mods have become popular.

The most popular by far is cutting a semi-circle into the mag body for more reliable feeding.  Apparently 458s sometimes get caught up on the edge of a standard AR-15 mag body. 

On standard USGI steel mags, slightly opening up the lips has been helpful, it changes the angle of the top cartridge, helping it "jump" over the mag body. 

Then there's the follower.  While the cradle like follower does make more sense for the rotund cartridge, I do not believe the 458 follower is absolutely necessary.  You can still load 223/556 in a mag modded for 458, and will only have a problem with the last few rounds.

 

[Displaced Texan 11,748]

The last link I posted are Magpul marked .458 mags….I don’t know if they can feed 5.56 from them. 
Is having a factory marked mag enough to show it is ‘only’ intended for the caliber specified? 

I also don’t know if owning a mag MARKED as .458 Socom will keep you out of NJ PMITA prison either..

 

 

[JohnnyB 4,325]

I just tried to order a10 rd .458 Socom mag from MidwayUSA. NO GO!

CMMG MkW-15 Magazine AR-15 458 SOCOM 10-Round Polymer Black

These products cannot be included with your order due to the following:

• State law restricts the sale of magazines over 10 rounds to New Jersey Customers.

 

[Scorpio64 5,155]

38 minutes ago, Displaced Texan said:

The last link I posted are Magpul marked .458 mags…

I went to MagPul's website looking for spex/pix and they do not seem to have a 458 specific mag.  The mag DSI offers is an aftermarket mod, with the follower changed and 458 laser engraved.

 

[JohnnyB 4,325]

Brownell's did not try to stop me. I then added a 30rd mag and they did not stop that either! Anyone else

ever try from Brownell's?

 

[Krdshrk 3,877]

1 minute ago, JohnnyB said:

Brownell's did not try to stop me. I then added a 30rd mag and they did not stop that either! Anyone else

ever try from Brownell's?

 

They'll stop you at checkout - not adding to cart.

[Scorpio64 5,155]

3 minutes ago, JohnnyB said:

ever try from Brownell's?

 

1 minute ago, Krdshrk said:

They'll stop you at checkout - not adding to cart.

Charlie Brownell's?

[JohnnyB 4,325]

1 minute ago, Krdshrk said:

They'll stop you at checkout - not adding to cart.

I made it all the way to "Place order" but I'm not hitting that button to find out!

[Scorpio64 5,155]

Just now, JohnnyB said:

but I'm not hitting that button to find out!

[Ferris 78]

Not sure if this helps or not but 450 bushmaster followers don't hold the first 2 5.56 rounds properly to  be useful for anything other than 450 bushmaster. So 10 rounds 450 BMs will only really work right with 450 BMs. I'm sure 450 Socom and beowulfs will be the same.