I posted in another thread about the upcoming changes to the GI Mag. In short they are moving to a new polymer follower, it is a more slick polymer akin to the Magpul follower material. The other changes are a modified feed lip angle and increased front wall height. The goal is to mimic the feed angle of Pmags.

Feed angle and spring strength, combined with the increased cyclic rate of the M4A1 is what brought about the need for the M4 Feed ramp. Until now this has been all that is needed to fix the issue of the GI magazine...That is until M855A1 came out, and then there was a new issue.

Now we have a hardened still tip hitting and riding the aluminum M4 cut which anyone can see will cause increased wear on the upper. I sadly do not have any M855A1 at my home to demonstrate this. So I went with a 70gr SMK, which is the longest bullet I have loaded. I used a Brownells tan follower magazine, and a Pmag MOE G2 to demonstrate the difference in feed angles and why the Army actually needs to modify the GI Mag if M855A1 is staying.

Gi mag.


If you can't tell the bullet is actually striking the area that transitions from the upper to the actual feed ramp. Now this is under the absolute most ideal circumstance for the magazine to feed. Had this been run in full auto on say a CQBR it would have been riding the M4 cut in the upper, and had it been M855A1 it would be wearing those feed ramps down.

Now compare that to the pmag.


Now the pmag is the ideal feed angle. Bullet strikes the feed ramp mid way completely bypassing the M4 cut ramps in the upper.

Hopefully the pictures demonstrate why feed angle is important and why they are trying to turn the GI Mag, into a PMAG.

Oh and here's the slide talking about the new GI Mag.


Typos are thanks to my phone, and I'm out for the night so don't expect a reply for a few hours.

Thanks for the info. Learn something new everyday.

I'll definitely find a way to get ahold of some of these.  

I think these are going to be best AR mag yet.

I'm not sure about the best AR mag yet, but it will be the best GI mag to date.

This is also a reason I take issues with Lancer's L5AWMs. They use the same feed angle as the standard GI magazine, which is what causes issues with M855A1. Now granted for the vast majority of use at this moment it doesn't really matter as M855A1 is limited to the Military and most do not run guns with a high enough cyclic rate to see an issue.

But it doesn't change the fact that L5AWMs should cause issues similar to the tan follower magazine when using M855A1. The only 2 magazines I know for sure offer proper feed angle is Pmags and ARC magazines. I have not had a chance to test Troy mags, ETS mags, or any other polymer magazine aside from those 3.

Hi,

It seems to me to be an ammunition problem not a magazine problem, the M855A1 is too hot for the M-4 carbine, and now the carbine/magazine has to be modified to run it.  It strikes me as the M855A1 is not a well designed round, the USGI magazine feeds it fine, its the ammo that's destructive to feed ramps.  Compare the M855A1 to to the newer NAMMO rounds which don't seem to be hard on M4 feed ramps.

NAMMO PDF


Just some thoughts:

It's both honestly. The M4A1 and CQBR run at a higher cyclic rate than the standard magazine was designed for, so M4 feed ramps we're created. M855A1 has an exposed hardened steel tip that will wear down aluminum. The GI magazine also has a less the idea feed angle, as it is more straight then angled upward.

Combine a high cyclic rate gun, a bullet with an exposed steel tip, and a magazine with a less than ideal feed angle and issues crop up. The easiest and cheapest way to fix this is the magazine. Pmags already have a higher feed angle than GI mags that remedies the issue, which is why the new GI mags will feature a similar feed angle to the PMAG.

It's a culmination of things that can be easily fixed by a cheap redesign of a cheap part.

Don'tuse m855.

If I'm using it, I'm down to my last, last,last ammo, and won't be too worried about feed ramps.

Txl

M855A1 is very different from M855, this appears to just be an issue with M855A1.

I guess that's why a Pmag would run a SAW on auto and a g.i.mag  wouldn't.

I saw that a long time ago and impressed the hell out of me.

I have limited experience (only a couple mags) but I fired a SAW on auto with GI mags.  It was at CMMG in MO about five years ago.  We shot about 100 rounds off a belt then a couple GI mags.  No feeding issues at all.

Yes. GI mags feed angle and the M4s cyclic rate we're causing the steel tip to nose dive into the M4 cut ramps and wearing them out. Instead of just adopting Pmags across the board the Army makes the GI Mag have a similar feed angle with the new feed lip and front wall geometry.

As my first post showed, even with an ideal amount of time for the follower to catch up my tan follower may was still pushing the bullet tip into the m4 cut in the upper.

Why would anyone need/want a squad automatic weapon that can  fire  magazines?  My understanding was that it had a heavier barrel that could be changed out and was BELT FED.  The MK 46 that I once had access to I believe didn't have the ability to use magazines.

And how many people on this forum own machine guns that fire exclusively M855A! ammo??

I think the military is quite content with the USGI magazine design.  They tweak it from time to time.  If they ever go to a polymer magazine (which won't happen any time soon) I suspect it will look like a Lancer magazine.

Hi Everyone,
While Lancer's original L5A mags did exhibit similarities to USGI's, The L5AWM was designed with a higher follower catch height and feedlips that feature a positive slope from back to front. This allows for a lower feed angle and a smoother and straighter transition from the magazine to the chamber.

Dan

For when one runs out of belted ammo.  

Or those of us playing with BumpSAWs. I use a bunch of 40rd PMags for mine.

 

When did this happen? All 20 of my L5AWMS feed nearly identical to my tan follower GI mags. Granted all were purchased 2 or so years ago.

Did ya'll try the Pmag Gen M2 as well?  How did it do?  I have both and have tried to give 'em an eyeball comparison and it appears that the M2 and M3 are very close in regards to ride height and feed angle.