Why does a .350 legend cartridge not properly fit in standard AR-15 mags?

M

MC_MuHyeon

Inactive
I've asked this question to people at Winchester via mail and I haven't heard from them yet.

Basically, .350 Legend is a straightened version of .223 Rem/5.56 Nato. So when I firstly saw the cartridge being introduced, I thought it would stack pretty well into already mass-produced AR-15 mags.

However, the reality was different from what I thought and people say standard AR mags don't always work well with the newborn cartridge.

So I made a hypothesis(?) that it's due to .350 Legend being slightly thicker than .223 Rem/5.56 Nato at the base (0.39 vs 0.376" in diameter)-thicker base means less room for another cartridge to be stacked when there is at least one already in the mag.

What are your opinions on the mag compatibility problem and my hypothesis?
 
The Legend(looks like a .30 Carbine on steroids) probably uses a different follower. I'm not seeing anything on any of the sites touting the Legend that even mention the AR other than Ruger chambering the AR-556 in it. It's more of a short range specific deer cartridge than an AR cartridge.
 
After reading a few other forums it sounds like the forward rib in the standard AR magazine is what causes the most issues. This can also cause problems with 300 Blackout depending on the bullet / magazine combo. With the little .223 bullet it doesn't cause any issues, with the .308 bullet it might cause a problem, with the .357 diameter bullet you need a magazine with the rib removed.

With a plastic magazine and the appropriate tool it could probably be done easily.
 
After reading a few other forums it sounds like the forward rib in the standard AR magazine is what causes the most issues. This can also cause problems with 300 Blackout depending on the bullet / magazine combo. With the little .223 bullet it doesn't cause any issues, with the .308 bullet it might cause a problem, with the .357 diameter bullet you need a magazine with the rib removed.

With a plastic magazine and the appropriate tool it could probably be done easily.
Click to expand...

I wonder if one could use a 300 blackout mag that Magpul sells? The front rib is thinned down to prevent the thicker bullets from making contact.
 
Basically, .350 Legend is a straightened version of .223 Rem/5.56 Nato. So when I firstly saw the cartridge being introduced, I thought it would stack pretty well into already mass-produced AR-15 mags.
Click to expand...
.350 Legend is a 'straightened .223' in the same sense that a Ford F-150 is an 'over-inflated Ranger'.

.350 Legend cannot be made from .223/5.56. Therefore, it is unique.

The reasons why it doesn't play nicely in some magazines have been addressed. Forward ribs 'squeeze' the cartridges at the front of the mag and screw up the geometry - especially in magazines that have 'slots' for the bullets to ride in. The larger base isn't really an issue. If it was, cartridges like .458 SOCOM would need bespoke magazines (like .450 Bushmaster...).
 
The front rib restricts it and its also a tad longer than my 300 ammo. I was thinking of trimming one of my 300 mags to have an extra mag. Since I have several 300 mags and only one 350 mag. But in retrospect, I will just buy an extra mag.
PS my 300 ammo will run through a standard 223/5.56 20rd steel mag. But rubs the front rib
 
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