Re: AR Barrel Length
If going with a straight prairie dog rifle, I like the 24" for the heavier forward weight, and they shoot very well too. The 20" is a good standard and I like a standard .750" gas block for a decent handling rifle. For calling coyotes I built an 18" barreled upper with a .675" gas block and a tapered barrel under the handguard. For as skinny as that barrel is it still shoots 3/4 MOA and is very light and handy with the ACE skeletal stock on the lower. I tend to choose barrel profiles more on the intended use as far as heft and balance vs. any perceived accuracy/velocity gains.