I know this is a old post, but I bought my M4 just over a year ago from Budsgunshop.
I run my bolt wet.
I have been firing regular/full power Remington 00 buck, slugs, and Sellier & Bellot 00 buck out of it so far with no issues.
I am very happy with the Benelli M4, I have since sold my Mossberg 930 SPX pistol grip and FN SLP off.
The M4 is worth every penny.