I am purchasing a new barrel for my ar10 .308 I have the option of an R5 1/10 or Douglas XX Premium 1/10 blank to start with.  I have two very reputable individuals I am working with.  Which is the better blank and why? (cause I said so doesn't work here)  I know everybody has their favorites and I am not interested in a flame war.  I would really appreciate the info prior to committing to a custom barrel.  Either way I don't think I can go wrong.  

Thank you in advance.

I am going to try and make a comment, I beleive the R5 you refer to will have a polyagonal?(spelling) type rifling like the H&K sniper rifle or Glock pistols, less bullet deform when bullet travel through barrel, where the Douglas will be std cut groove-lands rifling.

Douglas uses button rifling,where a "button" is pulled through the blank to rifle the barrel,no metal is removed, button rifling is considered to be more accurate than cut rifling,How this stacks up against polygonal rifling I don't know, I do know I recently had a AR rebarreled using a Stainless Douglas air-gaged 22" long,1-9 twist, At 100 yds it shoots 3/4" or less with 69,60,gr bullets,(10rnd groups) (am going to try some 53gr serrias tomorrow) at 200 so far, my best group was with 60gr hornady v-max, which measured 1 1/2" for a 10 rnd group I'm very happy with the douglas bbl, I don't think you could go wrong there,  The R5, I don't know so I can't really comment on it, maybe somebody who knows will....