Shu, If I were you I would go with a barrel length that with a youth stock installed the rifle would be the min. OAL, +that 1/2-1" safety extra in case you ever need to recrown, etc. By factoring for the youth stock rather than the adult size (and there is a difference between those with plain buttplate vs recoil pad), you, or the next owner, will have the option in the future and still be legal.