Grumulkin
Member
A 223 is a bit of overkill for deer. A deer taken at a bit over 250 yards with a 45 gr. Hornady Spire Point out of a 204 Ruger.
Twist isn't everything. Here's a target shot with 77 gr. BTHP match bullets out of a 1:10 twist barrel.
If you wish to shoot 70 grain bullets out of a 1:12 twist barrel, consider Speer 70 gr. Semi-Spitzers. One MOA groups out of 1:12 twist barrels is what I've gotten with them in several .224 caliber rifles and I've taken 2 deer with them.