I recently picked up a new M&P9 (Ser # HAHxxxx), as it was of post July 2012 production, I assumed it had a new barrel. Mark Housel put an RMR02 on it and I added the normal stippling, Apex Duty Kit, and Catalyst mag release:
http://i1292.photobucket.com/albums/...pseec933f2.jpg
Then I went to shoot it with Fed AE9FP 147 gr FMJ. Even when shot from the bench off sandbags, I still got 2-3 flyers in every 10 shot group at 25 yds:
http://i1292.photobucket.com/albums/...psa185e166.jpg
Thinking I might not know how to shoot anymore, I grabbed the G19 w/RMR02 and OEM barrel I carried all last year and shot a 10 rd group at 25 yds. I quickly realized there was a problem with the M&P9, not me, as the G19 shot fine:
http://i1292.photobucket.com/albums/...ps2e86bf36.jpg
Grabbed a known good older 1/18 twist M&P9 upper assembly I had and dropped it on the new lower--shot a bit better:
http://i1292.photobucket.com/albums/...ps7dd7b573.jpg
Next, tried putting a KKM drop-in barrel I had lying around in the new M&P9:
http://i1292.photobucket.com/albums/...ps2a25b807.jpg
Shot pretty good, so this is what I used at the recent Ken Hackathorn class: http://pistol-forum.com/showthread.p...stro-Valley-CA
Now I was still curious why the M&P9 shot so badly with the OEM barrel. After looking at it, I noticed there was no dimple on the underside of the barrel--thus indicating an older 1/18 twist barrel, as shown by Hilton Yam at MSW: http://modernserviceweapons.com/?p=3719 Careful inspection of twist rate indicated it was an old 1/18 twist barrel.
S&W was kind enough to send me a new 1/10 twist M&P9 barrel w/dimple to replace the older 1/18 barrel that some how inadvertently had been put in my pistol as it was being built.
When I tried the new 1/10 twist OEM replacement barrel in my new M&P9, the results were not ideal despite trying several groups:
http://i1292.photobucket.com/albums/...psb5b350e2.jpg
http://i1292.photobucket.com/albums/...ps17b9f750.jpg
Finally I dropped the KKM barrel back in and got a reasonable group:
http://i1292.photobucket.com/albums/...pse1e5d509.jpg
Bizzarre...