I've owed my Core 15 M4 Scout for less than a year. I've shot @500 rounds so far, which was a mix of different type reloads as well as factory rounds. So far, it has operated very good with no failure for feed and function, plus the accuracy has been very good but keep in mind the longest distance was only 100 yards. I've used Steel Vietnam era mags, aluminum mags and Magpul with no issues.
So far I've only ck'ed accuracy as a defense weapon, for center mass type/size targets. I also own a 90's era Bushmaster DCM that I used to shoot in NRA High Power matches. The Bushmaster was capable of slightly bigger than 0.5 MOA. This week I hope to find time to ck the M4 out using match grade ammo that I loaded with Sierra Matchking 69gr bullets. I realize it will not shoot as accurate as my Bushmaster but it will be interesting to see how it compares.
The M4 is well built and in my opinion a great value for the cost, especially considering it was less than $600. Normal retail is over $900, but Core15 takes a few guns (various models) to trade-shows several times a year and allow potential stores to test fire them. I just happened to be at their store when they had a few trade-show guns marked down due to 200-300 rounds fired at the show. As far as I was concerned they broke the gun in for me at their cost
I believe they will tell you if they have any trade-show sample guns available if you call them but I do not know if they only sell them locally (Ocala, Fl).
I also have a few friends who own one of their AR's but different models than mine. All are very satisfied...
Hope this helps.
http://www.core15.com/