Re: Follower or clip mag feed for bench accuracy?
You could just try it and see, just to verify in your own rifle, but I'd go with the single feed. The transition from magazine to feedramp to chamber is not a gentile one. There's another point to consider here as well; OAL. Not the OAL you set when you loaded the rounds, but the OAL they'll reset themselves to when you trip the bolt. You're dealing with a very large and expensive kinetic bullet puller there, especially with the added mass of an AR-10 platform. I've never seen an AR-15 that wouldn't pull the bullets to some degree during chambering. This can go from very slightly (but still measurably) with mil spec ammo using neck sealant and a crimp, to quite dramatically when using minimal neck tension in match loads. Bottom line, and I keep repeating this, Service Rifles (autos in general) are not bolt guns, and they need to be treated very differently.
You've got a significantly different situation here than you do with M1s and M14s (which should NEVER be fed directly into the chamber), where this sort of action risks a slam-fire. These guns MUST be fed through a magazine, simply to retard the bolt velocity a bit as the gun goes into battery.
From a bench, I'd probably feed directly into a chamber, and close the bolt gently as possible.