Boudin,

Two things I like about this forum; good people, and I learn something every day. The CORE 15 M4 mid-length has a 3 groove polygonal rifling. I did not know that existed in the AR platform. Any idea who makes this barrel?

I guess you are comparing the M&P15 VTAC to the non-piston CORE, both mid-length systems. Otherwise it's apples & oranges. Good specs and accessories on the CORE, but that stainless steel 3 groove barrel is an unknown. Depending on the barrel manufacturer, stainless should be very accurate, but the VTAC has the melonite 5R barrel which we all know is very accurate. Given equal cost and typical consumer shooting, I would go with the 5R every time. However, the VTAC is a bit more money which muddles everything, and then what value do you place on good customer service.

Whichever weapon you choose, good luck and let us know how it turns out.

Added - A quick search showed me 3 barrel manufacturers doing 3-groove barrels; Lilja, Rainier, Pac-Nor. I'm sure there are more. Mixed, inconsistent reviews on the barrel, none of them on .223/5.56 cal.