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It could be worse..... you cold still be buying P7 mags @ $50+ for a 8 rounds

all jokes aside.... if money is the issue here.... CDNN sells SW99 mags that work perfectly in the P99 and are cheap at.....they might not have as nice of a finish but work just as good as the P99 mags and hold 16 rounds.....
also if you have a Sportsman warehouse close... they may have the 15 round P99 mags for $35, or if you are lucky they are still on the old pricelist @ $24

 

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while it might work......
due to mag restrictions in some states there is different ways of ordering a P99
10 rounders or 12 and 15 rounders for non restricted states....