Are the 300 BLK mags on the market a real necessity to shoot the caliber in an AR? Are there actual feeding issues caused by using 300 BLK in a 5.56 mag?

Absolute necessity, no. Preferred, yes. The main issue with using 5.56 magazines is the strength of the magazine spring. 300BLK will wear out a 5.56 spring relatively fast due to the additional weight of the bullets, especially so when using subsonic loads that can have projectiles that are close to 4 times the weight of the typical 55gr bullets that are used for XM193, for instance.

As everyone probably knows, AR magazines have stiffening ribs on the interior surface of the mags. Because of the larger diameter of 300 Blackout bullets, they contact the front ribs that were designed for 0.224" bullets and that don’t touch the ribs. That causes the bullets of 300 BLK cartridges to be pushed at a slight angle toward the center of the magazines rather than being absolutely parallel with the barrel bore. The dedicated 300 BLK magazines I’m familiar with have lower/less prominent ribs and they don’t push the cartridges off line to that degree. I believe that may be why 223/5.56 mags hold fewer 300 BLK rounds than the cartridges they’re designed for.

In any event, I and the other people I know who have 300 BLK ARs use 223/5.56 magazines without any functioning problems.

I'll just leave this here...

quote:

Originally posted by nhracecraft:
I'll just leave this here...

Thanks. That pointed out the ribs I was referring to. I haven’t done too much with the heavier subsonic loads from full magazines and wasn’t aware of the slow feeding issue.

My Rattler came with a Lancer 5.56 mag and I bought some extras. Due to the ammo situation I haven't shot the thing yet though. Not sure if they have the same issue as the Magpuls in the video.

A lot of the reason for dedicated 300BLK mags is to avoid mixing up your ammo and putting the wrong mag in.

Local shop had a 5.56 upper that someone accidentally put a mag of 300BLK in, getting mixed up at the range when their friend/relative was shooting 300BLK. Not a mistake you want to make.

I prefer the Lancer dedicated 300 BO magazines.

I have a few GI mags that have a modified spring and feed lips that I am going to try this weekend. (a friend did the mods so we will see)

The best reason for a dedicated mag, or a different color mag is that a .300BO will chamber and fire in a 5.56 AR, and the results can be catastrophic. Sometimes you get a really long swaged bullet, and sometimes you get a complete and violent disassembly of the rifle. Neither is good.

A friend of mine who has both has black magazines and kit for his 5.56, and FDE magazines and kit for his .300BO to avoid this very problem.

I haven’t been able to find the magazines I like in different colors, and I don’t like painting them, therefore my 300 Blackout mags have identification bands. There are at least a couple of different types:

https://www.amazon.com/Sightho...arking/dp/B07MVFMN8T
https://www.ammobands.com/

quote:

Originally posted by Lefty Sig:

A lot of the reason for dedicated 300BLK mags is to avoid mixing up your ammo and putting the wrong mag in.

Local shop had a 5.56 upper that someone accidentally put a mag of 300BLK in, getting mixed up at the range when their friend/relative was shooting 300BLK. Not a mistake you want to make.

Better feeding and preventing mix ups.

This is what a .300 b/o bullet looks like after traveling most of the way through a 5.56 barrel:

^^^ Damn that's like a cartoon effect.

My only .300 BLK is an FDE colored Tavor X95. The only FDE colored magazines I own are those used with this firearm and loaded with this ammunition. It really avoids confusion.

I only use my black pmags for 300BO
My USGI mags are for 5.56

I follow the same practice - FDE mags (or FDE MagPul magazine pulls) on magazines loaded with .300 Blackout.

Lancer recommends their 5.56 magazines for supersonic .300 Blackout and their .300 Blackout magazines for subsonic.

I use ETS mags for my 300 blackout, and pmags for 5.56. Very easy to identify.

quote:

A lot of the reason for dedicated 300BLK mags is to avoid mixing up your ammo and putting the wrong mag in.

Easily done by specialized markings.

My local shop laser engraves Magpul magazines with the caliber.

I also use a bright yellow electrical tape around the magazine to differentiate them.

I've shot quite a lot of ammo, both sub and supersonic using a standard GI and Magpul magazines with zero issues.

I'd just put colored electrical tape on them to differentiate. I put red tape around my range/training/beater mags, and I have some blue tape I haven't used yet, which I can put on 300 mags.

I'll probably pick up some of the Lancer mags. I generally prefer them to Magpul.

I’ve got elastic bands marked 300 BO wrapped around the lower part of each mag.

I have had feeding issues using 556 mag with 300BO. I bought magpul mags for 300 ad they have been flawless.

Just ordered 4 Lancer mags.

Would have gotten more but I was primarily ordering 7.62 ammo and, well, I don't even have a 300 BLK AR setup yet. Just preparing for the future....