For several years now Mec-Gar has manufactured 9mm magazines for the FN Hi Power, whether sold under the FN logo or Browning’s. The standard-capacity 9mm Hi Power magazine is 13-rounds unless legal impositions demand the 10-round versions.
This Mk III is shown with a Mec-Gar 13-shot magazines. If you look carefully below the last witness hole on the side of the magazine, you can see the number “13”. Not all Mec-Gar magazines are marked in the same way. For whatever reasons, Mec-Gar magazines have sported variations in both markings and witness hole locations on the magazine body. In my experience, Mec-Gar is the premier Hi Power magazine for reliability, shot after shot after shot. It has been my first choice in Hi Power magazines for decades now.
Mec-Gar also offers 15-shot 9mm Hi Power magazines and has for years. It is a popular magazine with Hi Power users and one that frequently garners questions on Internet firearm forums. The two I see the most are: “Does the 15-round Mec-Gar extend below the butt of the gun or is it flush,” and, “Are they reliable”?
On the left is a Mec-Gar 13-round Hi Power magazine and on the right, a 15-shot one. They are the same length. The 15-round magazine appears no different when seated in the Hi Power than the standard-capacity 13-shot. Look at the lower right on each magazine and you will their capacity notated along with the Mec-Gar’s initials and “BRHP” for “Browning Hi Power”.
The way Mec-Gar accomplishes this is by using a shortened magazine follower which as a hollow base.
On the left are two versions of the Mec-Gar 13-shot 9mm magazine followers. Most of mine are the type having two “legs” though some of are like the “skirted” follower pictured with it. Some of my Browning-marked old “Law Enforcement/Gov’t Use Only” from the days of the Clinton ban on “high-capacity magazines and feeding devices” are of the skirted type. I have not found either of these 13-shot followers more reliable than the other. The picture on the right shows the 15-shot magazine follower. Notice that it is shorter than either of the 13-shot followers. It is also hollow.
Here is another view of Mec-Gar’s 15-shot magazine follower that more clearly shows the hollow follower.
In my experience, I have not found the 15-shot Mec-Gar magazine to be less reliable than the 13-shot versions with one exception; they sometimes do not engaged the slide lock when the last round is fired where the standard 13-shot versions very rarely ever fail to do so. Over the long-term, both 13 and 15-shot Mec-Gars have fed varied types of JHP’s flawlessly in my Hi Powers.
I have purposely left a couple of 13 and 15-round magazines loaded to full-capacity for just over two years to see if this weakened them and thus lowered their reliability. Each was loaded with a rather blunt ogive handload using Sierra’s 115-gr. PJHP. Each magazine functioned perfectly; all rounds were fired and the slide was locked back after the final shot with each magazine. It is said that as long as a magazine spring is not compressed beyond its design limits, it is not damaged by being left loaded long-term. I cannot say if that is always true, but it seems to be with these Mec-Gar magazines.
Best.