Yes the difference between a .308" bullet, and a .311" bore is small. The chronograph proves the differance matters. How much it matters depends on the individual, and their wants and needs.
Letter to Hornady Customer Service:
Me - "Great to see you've introduced the new 7.62x39 ammo with the V-Max
bullets! I'm wondering how soon, we may expect to see just the .310" V-Max bullet
available for reloaders?"
The reply - "Thank you for your inquiry. We are always working on New Products. We
will take your suggestion into consideration. Please watch our website
for announcement of New Products late December/January."
I'm only guessing they went with .310" to bridge the gap between the mini-thirty and all other 7.62 rifles.