To truly answer that one, I'd have to do a little casting of the barrel innards with cero-safe. The first shot flier can be a lot of things - some barrels shoot the first round off simply due to different friction when really clean, or due to a lack of stress relief when they were made (which is fixable with a heat treat). Minor crown issues can also do that - I re-crown almost every barrel I own and that's that (easy in the lathe, sometimes don't even have to remove the stock)
It could also just be getting so fouled that it won't shoot. When I compete, I clean every few rounds as at least that always puts me into a known state. For competition I almost always use moly coated bullets which cuts that fouling way way down as well - those take awhile to start grouping in if you've cleaned all the moly out of the barrel, but that's so hard to do in practice it's not much of an issue unless you use bore paste (abrasive) which you don't do often - can't put metal back after all.
A fluted barrel will cool better, but the truth is - if you shoot very fast, the inside temp is always a lot hotter than the outside. For an instant, it's red hot right after the bullet goes by, and steel is a crappy heat conductor.
Do you have the typical 1::9 twist? That should do with most ammo, but I find my best results with 53 gr sierra flatbase in mine, with straight ammo (no runout). No factory or mil ammo is straight, and with the otherwise sloppy fit in a NATO chamber, it's hard to get them to shoot in the best of times.
On the other hand, here's a target at the same range from my AR after *extensive* work, 5 rounds in 10 seconds, off bags. I keep it in my wallet so it shows when some clerk asks me for my ID, next to the CCW permit and voter card. It's not a fluke - another guy shot one just like it half an hour later with everything else the same and him not as experienced a shooter.
Note, this would be a downright embarrassing target to shoot benchrest at 100 yds. But it's not bad for an AR and going very fast.