Whenever I buy magazines, I look for bulk deals. For instance, every once in a while, Brownells will have a deal on a 10 pack of PMags (not now but they do regularly enough). And sometimes you can get them for just north of $10 each.
Anyway, I found a deal on another site for some M&P9 magazines. So, I snatched some up. When they got here, I realized they were 15 round magazines:

I was a little bummed. I guess they were made for places outside of America, like New Jersey or Maryland or something. They were the same size as the 17 rounders I’m used to, so I decided to take them apart and see what made them 2 shy of a full load:

Seems they compressed a bunch of extra spring at the end of the spring. I suppose I could just order replacement springs. But I grabbed some wire cutters instead and cut off the unnecessary portion of the spring:

They loaded 17 rounds just fine. I’ll check reliability at the next range trip. I may end up buying those replacement springs anyway.
*Wile E Coyote School of Gunsmithing