I very much doubt that a barrel with only 5-8K rounds through it is shot out. There has been some discussion on other forums of the well known poor accuracy with the 9mm M&Ps, and as I recall, it had something to do with poor barrel fit in some manner. I'm not in a position to search for the strings now, but it was probably on pistol-forum, and I am almost certain the link I followed to it was on LF.

One of the options provided above is a fitted Apex barrel, and that might be a good place to start. I believe that they have a complete shop and pretty broad options, so you might find it worthwhile to research it and work from there.

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NHI, 10-8.