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I'm assuming you are shooting jacketed bullets ... make sure the rifling on your M&P9 are not fouled by copper.
If rifling is pretty much filled up, there's not enough grip on the bullet so you are essentially shooting on smooth bore (with no rifling), ending up with a highly unstable bullet. Same thing if you are shooting lead.
Your regular Hoppe's #9 don't remove lead or copper fouling much.
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