In the original post, it sounds like the problem is with an M&P 15-22. Have you tried different brands of 22s? Have you inspected the bore to see if the lands and grooves are distinct? It is possible that the bullets in your 22s are undersized, and it is possible that the problem lies with the barrel! It is possible that the barrel is severely fouled, or that the rifling is not fully cut. It is also possible that a 0.224 centerfire barrel was mistakenly in with rimfire barrels. If the bore is clear of lead fouling, let the job fall in S&W's hands under warranty!

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Judge control not gun control!