I've heard of two different types of factory hi-cap mags for the Walther P99 series. One is the "normal" 16 round 9mm mag. The other is a 15 round mag. So far I have only seen the 15 round variant in non-LEO form. I'll add text & pictures as I can.
10 round mags
They're not hi capacity, but they are factory, so I have to mention them. Basically, they run great, but the fact that they have to make them disgusts me. I hope that they are turned into collector's items next year. Go here (AW Ban Sunset) to see what you can do to help make sure that happens.
15 round mags
The 15 round mags I've seen have the Walther factory markings on
one side and MecGar markings on the other. They have three witness holes marked
for 5, 10 and 15 rounds. Some claim that you can fit 16 in these 15 round mags.
Technically they're right, but I would not do this. To get the 16'th round in
you really have to shove on the bullet. Once you get it in, the mag will not
seat properly in the pistol when the slide is in battery (forward). You can get
it to lock in, but you have to give it a really hefty smack on the bottom - way
to hard a smack to indicate proper fit & function. In a really scary oddity, if
you shove one of these mags loaded to 16 in when the slide is closed and fail to
smack the base of the mag really hard, the mag will set there as if it's in, but
it's only there by friction.
I will be examining a LEO 16 round mag soon. I expect to find differences in the follower and possibly the spring also. Until I see exactly what the difference is, I will not be putting that 16'th round in the mag. The chance of damaging the spring and/or follower, and the possibility that the mag will not seat properly is enough to keep me from doing it until I know better.
Update: Well... I hate to do it, but I may have to admit I was wrong. I just had the opportunity to dissect a factory 10, a factory 15, a factory LEO 16 and a S&W LEO 16. Of course, that abomination - the 10 rounder - was quite different. Examining the 15 and both LEO 16s was surprising. The biggest difference between the three was that the S&W follower was white. Physically the three followers looked identical. The Walther 15 & 16 even had the same type/lot markings on them. The springs were identical, and except for the molded in name, the baseplates all matched too.
Pictures will be coming soon.... Are here.
Since they combine examples of all the factory mag types I have access to, they
will be presented together at the bottom of the page.
16 round mags
So far the only P99 magazines I've found that are marked for 16 rounds are LEO. If you have a non-LEO 16 round marked P99 mag, please take some good pictures of it and email them to me. (Cranky@CrankyLabs.com If you could take them apart, pics & dimensions of the parts would be appreciated.
Comparison Pictures
This picture shows completely dissected mags - Walther 10 rounder, one of the 15 round pre-ban mags, a Smith & Wesson SW99 LEO mag and a Walther P99 LEO mag.
The following pictures showing the mag bodies in the same order. (Walther 10, Walther 15, SW LEO 16, Walther LEO 16) Note that the SW99 mag has the LEO markings on the front and the Walther has the LEO marks on the back.
These pictures show the innards of the respective mags. Again, they are in the same order.
I thought that the springs in the 15 and 16 (marked capacity) mags might be different. These pictures show that they are not. Except for the deviant 10 round mag, they are all identical in the shapes and number of coils. The material appeared to be the same too. In the second picture you can see how similar they are - that's a spring from the 15 and a pring from a 16 laid out together.
Using the 10 round mag body to keep everything aligned, you can see that the preban 15 and both LEO 16's have identically shaped bodies. They may be off in very small ways, but I was unable to see how.
UNSUBSTATIATED RUMOR - "Turkish 15 round mags"
I found this posted on one of the auction sites. I cannot verify it as true or false yet....
These are the so called Turkish mags. They were not made in Turkey read on.....They are brand new. There is only one meaning for new. That means never loaded or inserted in a gun, these are NEW. They were originally shipped to Turkey where there is a 15 rd limit like our 10 rd limit. They were recalled and had the overlarge follower replaced by the normal one which restored their capacity to 16 rds. Nothing was done about the last witness mark still reading 15. They do hold 16 rds. They are made by MecGar for Walther and have both logos on them.