I am looking to get a flat top upper and was wondering if the varmint barrels are more accurate than say a heavy barrel with some kind of crown or is a heavy barrel flat top with front site just as accurate I would like to use it on groundhogs and some target shooting just thought I would ask the experts. Now where can I get an affordable flat top upper that shoots good
Thanks Mike

The most accurate out of the box AR barrel is the Olympic Arms Ultramatch, no contest.

I have the standard chrome lined 20" H Bar Bushmaster (V-Match upper) and it shoots near 0.25 MOA.  I reckon thats good enough for varmints!

Barrel weight, or contour, by itself has zero effect on the accuracy of a barrel.  Thicker barrels resist heating longer than a thin barrel, but they also disipate heat more slowly.  With that said, if you're looking for a barrel for a flat top varmint rig it kinda' depends on how much money you want to spend.  Not personally familiar with the Ultramatch, but I've seen very good results with the Bushmaster V Match and Varminter barrels.  You can also go the custom route with barrels from Douglas, Krieger, etc.  The most accurate "factory" barrel I've personally seen is a Bushy Varminter that put the first 5 shots after break in into .088" at 100 yards.