Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
I actually run a 4.00 / 18 on the rear of my 500/550's and don't have any issues. (Yet). I'm sure the more senior / experienced members on the forum will shoot me down. I run continental rb2/k112 and really like them. M&P do good deals on a pair...https://www.ebay.co.uk/itm/141307000267