I did a look through the search feature and could not find an answer to this question, so please excuse me if its been asked and answered.

I got 2 magazines with my Police Trade-in M&P 40. They are marked 357/40 and have round holds for the retainer in the center of the base plate and have the S&W logo without words.

I bought 3 additional magazines from AIM Surplus which arrived yesterday and they are also marked 357/40. They look unissued even though they were marketed as surplus. However, they have a square opening at the rear of the baseplate and the S&W logo is bracketed by the words Military & Police.

They seem to function the same without going to the range. Is there anything I should know about the ones with the square opening? I've pulled the original pair apart and cleaned and oiled them, inspected the springs, etc. without a problem. Just wondering if there are any surprises with the new ones in store for me, or any known problems with either type?

Thanks.

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Yes there have been changes to both the followers and baseplates over time.

The baseplates with the round button on the bottom were replaced because in some situations the magazines could come apart when dropped or perhaps during reloads (I think if you dropped it on something pointy that just happened to depress the round button, or somehow managed to depress the button with a ring or something during a reload). The square switch baseplate is the newer design, although in practice I've never had an issue with either one.

The only issue I've had with M&P magazines is some 9mm followers preventing magazines from dropping free when the mag release was pressed. Switching followers to the latest design fixed them.

Thanks. Good to know that the "surplus" magazines that I just got, that look unissued, are the newer model. They were cheap, fit, drop free, and are the newer model - what more could I ask. Appreciate the info.

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You can see the changes to the base plates in this photo of all 5 of my M&P magazines. I'm using the original 2 (top row) for 357 Sig and the newer 3 (2nd and 3rd rows) for 40S&W.

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^ I like your case!

Thanks. Did the cutting today. Started with a Sam's pelican-knockoff that cost me $19 after Christmas and a good sharp knife. I'm pretty happy with how it turned out too.

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Yes the 40 and 9mm followers have changed. Take a look at this pic:

See how the front corner is different? They had a problem with that corner engaging the slide stop. Squaring it off seems to have fixed the issue.

This did help eject an empty mag, but did nothing for mags with more than one round in them. My 40S&W mags still stick a little.

The round vs square hold in the base plate makes absolutely no difference. I don't know why they did it. The round hole is not susceptible to coming apart any more than the square hole. I have both versions and have used both extensively. Never had one come apart.

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Thanks. The internals are different too. On the older magazines with the round hole the internal plate is attached to the spring, while on the newer ones with square holes there is a plastic plate that sits on the spring but is not attached.

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Just a follow up to the magazines and their functioning. No problems with any of the 5 with either 40SW or 357Sig ammo after nearly 5 months of use and visits to the range. All of them, old and new, are still excellent. Once I added a Hogue Handall Tactical Grip Sleeve it's become one of my most accurate weapons other than my MkII Target pistol. Thanks again for the help.

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PPS1980, I too bought spare mags from Aim Surplus and they looked to be brand new, not a scratch on them. All work perfect, and all have the square hole butt-plate. Awesome price too!