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The original plastic follower design has a long center post, designed to prevent spring over-compression, and a short anti-tilt leg in the rear. It does not have any anti-tilt leg in the front, which means that the rear of the follower can tilt down and fail to push the rounds up to the feed lips. This results in both bullet-feed misalignments (jams) and in "bolt-over-bullet" fails to feed. The latter is especially common on the last couple of rounds in the mag, when spring pressure on the follower is the lowest. This happens whether or not mags are loaded to capacity or underloaded, and is completely independant of the ammo type used. It is simply a result of poor follower design.

This problem had been an issue with the 30-round mags ever since they had been adopted. In the mid-80s, it was noticed that the problem seemed to happen more frequently with Sanchez-brand magazines, and so an investigation was started to try to determine the cause. It was assumed that the investigation would determine that Sanchez mags were not in-spec. This turned out not to be the case, and the final recommendation was to correct the design of the follower. Thus, new followers with a front anti-tilt leg were created, which used green plastic to make them easy to identify, and were shipped with new Sanchez mags starting in 1988 for field trials. The trial ran through 1990, and proved to be successful at eliminating the feed problems associated with the original followers, resulting in formal adoption of the new design in 1991. All USGI-contract 30-round AR mags were required to have the anti-tilt followers as of late '91. Existing black-follower mags were not upgraded.

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You have to decide for yourself how reliable you expect your mags to be. While millions of BF mags exist and have been used, there have been lots of feed problems that are directly attributable to the design of the BFs. GFs are known to significantly reduce or eliminate these problems. Upgrading costs $1.00-1.50 per mag, depending on quanity. Is it worth it? That's a question only you can answer for yourself.

All of my USGI 30s have GFs.

-Troy

Look for that FAQ coming soon!  [:)]

-Troy

Due to the thickness of the alloy follower in the 20-rounders, the follower tended to track pretty well in the mag.  Plus, the mag body was straight, which also helped.

There were problems with the first 30-rounders (the Colt ones with the dark green followers with white part numbers stamped on them), and some subtle changes were made to the mag body and spring to fix them.  They SHOULD have modified the follower at that time to an anti-tilt design (well, actually, it SHOULD have been right from the beginning...), but didn't do so until the late 80s/early 90s.

-Troy

Also, there was no GOOD reason to only load 18 rounds in the mag, but here's why it happened:

In the beginning, M193 ammo was issued in boxes, loose.  GIs would typically dump out the boxes into their ponchos and proceed to load their mags.  Sometimes, they would overload the mags, as you can force 21 (and sometimes 22) rounds into the mag.  This is BAD, of course, and can (and usually will) cause a failure to feed.  This was eventually fixed by issuing the ammo on loaded stripper clips.  1 mag = 2 clips of ammo.

The other problem was that GIs would disassemble their mags for cleaning and remove the follower from the spring.  Because the spring connected to the follower in almost the center, it was easy to put the follower back on the spring backwards.  You wouldn't notice a problem until you tried to load the mag.  That's when you'd notice that it was difficult to put more than 18 rounds in the mag, and if you forced the last two in, it would bind the follower and you'd have no spring pressure to feed the ammo.  This was "solved" by instructing GIs never to remove the followers from the spring (though of course I'm sure it still happened sometimes).

By '68 or so, most units were correctly filling their 20 round mags with 20 rounds, and not having any problems.  But some units, who were trained the "old" way and/or who believed all of the myths and mistruths that were spread about the M16, would still train the "18 in a 20" method.  Some folks STILL underload their mags to this day, and there is NO reason to do so.

Well, okay, there is ONE reason that makes sense:

Underloading your mags by ONE (1) round will make it easier to to a "tactical reload", which is where you remove a half-empty mag and replace it with a full mag during a lull in the fighting.  When you do this, your bolt will be forward on a loaded chamber, and if your mags are full, you have to give the mag a FIRM smack on the bottom in order to compress the spring enough to allow the mag to lock into place.  If you fail to do this well enough, the mag will often fall out of the gun on the next shot.  Underloading the mag will leave more slack in the spring, and make reloading with the bolt forward a bit easier.

I still prefer to load to capacity.  As long as you understand the big picture, this is no problem.

-Troy

With USGI mags, it is absolutely NOT necessary to download mags for the purpose of either preventing spring set or to ensure operational reliabiliy.  However, some folks will download by one round to make tactical reloads (reloads where the bolt is forward on a live round) easier.  A full mag doesn't have much slack space, and takes a firm smack on the bottom to ensure it is fully seated when the bolt is forward.  Downloading by one round reduces the force necessary to seat the mag.

Myself, I just prefer to use a firm smack and have fully loaded mags.  Neither method is right or wrong.

-Troy

Where did you get your GFs from?  The green and orange followers *should* be identical, but there were some cheapie aftermarket GFs going around that people had problems with.

-Troy

Simple.  Buy some wooden dowels.  Cut to approx length (start long, so you can adjust down), until the mags hold only 15 rounds.  Make more dowels, and send to the person you're buying the mags from.  Have him install the dowels and ship you the mags.  Perfectly legal and NJ folks have been doing this for years.  NJ law does not require the block to be permanent.

-Troy

Sorry guys.  My information on that issue is out of date.  It seems that a year ago or so, the AG of NJ "reinterpreted" the issue, and now mags must be permanently blocked to 15 rounds, despite 10+ years of allowing temporary blocks.

-Troy