Most Popular Barrel Length for 6mmARC?

[danm]

I'm gonna say 18"... Only because that's what I have and it seems that's the length it was supposedly designed around?

Hmmm - - You may be and probably are right, but I doubt one will achieve the touted 2750 fps out of the Hornady "Black" 6mm ARC ammo with the 105 gr bullet out of that length barrel.  FWIW I also doubt one would get there with my suggested 20" barrel either.  With my work with the 6mmAR, we found that velocity seemed to peak around 25", although there was very little increase between 24" to 25".  The proven method for determining this was by taking a couple 28" barreled uppers and a hack saw with a hand crowning tool with the chronograph (as well as plenty of weighed charges ammo) to the range and chronographing 5 shots, then saw and inch off the barrels, then go again, then saw and inch off, etc.  That method really gives true data on barrel length vs velocity.


Yeah just doing my drop at 525 yrds 3.4-3.5 mils I'm calculating 2650 Proof 18" Carbon.... Don't have a chrono, I know... Tisk tisk. I don't reload yet but plan to eventually and obviously save all my brass... Got a ton of Grendel and 40 6ARC so far.....

I got mine as a 20”, for the basic reasoning you mention.  It’s also rlgs which is doing fine. 
However for a top-tier barrel maybe 20” is the min I’d think...?
The 105 black I’ve shot get, 2665; it’s early and my brain is not awake yet.  The 103 eldx loads I can get 2700 with lever but for now my node seems to be 2681.  But it’s mainly intended for hunting not competition.