The ideal magazine depends on the shooting task at hand
Few firearm components have seen as much political interest as the AR-15 magazine. Anything that draws the attention of politicians (and a potential ban) is worth understanding, owning, and voting to protect. Deciding to own a few extra AR-15 magazines is always a good idea, but the issue of which magazines to buy almost always surfaces. Do you go with 10-, 20-, 30-, or 40-rounds?
The first decision to make is how much capacity to purchase. So often, the default answer is 30 rounds and that’s a good one. 30-round magazines are really a standard capacity and most of the AR-15 aftermarket is set up to support them. All of the magazine carriers and pouches fit 30-round mags. Most of the magazines I own are 30-rounders because I’ve always used them and so have most people.
30-round magazines work well with most of the shooting activities associated with the AR-15. Whether it’s plinking at the range or fighting in a war, having thirty rounds on tap offers plentiful capacity without being overly heavy or cumbersome. The AR-15 isn’t noticeably different to fire or manipulate with these magazines.
Less Can Be More
Stepping away from 30-round magazines is where we see some specialization for specific needs. The mildest deviation from a 30-round magazine is the 20-round magazine. The 20-rounder offers good capacity in a more portable package. These are the magazines I reach for when shooting an AR-15 from the bench because they offer the maximum number of rounds without interfering with shooting from the prone position or from the bench. Rifles are usually easiest to shoot accurately when placed as close to the ground as possible. The lower they are the easier they are to stabilize. 20-rounders are perfect for this task.
20-round magazines also tuck into a pants pocket much easier than a 30-round magazine and are at least twice as likely to stay in the pocket when moving around. Sure, kids these days have chest carriers and magazine pouches galore, but I still find myself throwing a spare magazine or two in a pants pocket from time to time. Nothing is better in this capacity than a 20-round magazine.
10- and 40-round magazines are highly specialized and it’s usually not necessary to own more than one or two. 10-round magazines sit almost completely flush with the bottom of the magazine well and are useful when any protrusion at all would interfere with the shooting position. The only time I’ve seen this feature come in handy is when using a shooting bag on which to balance the rifle. The center of the rifle is usually where the shooter wants to place the bag and protrusions in this area make stabilizing the rifle difficult. 10-round magazines are also the only magazines legal in some restricted states.
40-round magazines are useful in competition with multiple targets or in home defense scenarios where there’s no such thing as having too much ammo. It’s highly unlikely that much ammunition will ever be required for home defense, but it’ll certainly be comforting. Also, home defense scenarios usually don’t last long, so the extra weight from the magazine isn’t much of a penalty.
Metal or Polymer?
Metal magazines represent the old guard but they still do an excellent job. I like to keep a stock of aluminum magazines because they’ve been around for so long, manufacturers worked the bugs out long ago. All they need to move from good to great is an anti-tilt follower. Resist the urge to “stretch the springs” because that greatly shortens the spring’s lifecycle.
One advantage metal magazines have over polymer magazines are the speed with which they eject from the magazine well. Sometimes polymer magazines can be a little slow to eject (especially with variations in mag well dimensions), but aluminum magazines always seem to hustle out of the way. Polymer sliding across aluminum is slower than aluminum sliding across aluminum.
Polymer magazines have the advantage of price and crush resistance. Not only are polymer magazines less expensive than quality aluminum ones, they can handle impact and crushing loads better because they are less likely to permanently deform. Where aluminum bends or dimples, polymer just flexes and returns to its initial shape.
Magazines are a serious consideration for an AR-15 and just about everyone will be best served by a mix of aluminum and polymer magazines of varying capacities. 20- and 30-round magazines are the sweet spot.