Short of cloning the entire rig with a Uberti scope and all for grins (will have not resale vaule since it will be a clone),


Going from 270 to 30-06 is really the long way to go for long range shooting.

The 270 shoots flatter for the same yardage you will be pushing the rifle in 30-06, and will be more accurate isntead.

Truth be told, the Win 70 action was short lived, with the M40 in 308 became the major player instead.  And to take it one step farther, in a non military role, the 243 is the better round over the 308, since again it shoots much flatter for the ranges that the rifle will be pushed.

Hence all the calibers stated above use the same bolt face diameter, so it really boils down to the use of the rifle, the ranges it going to be pushed, and the scope system on the rig to accommodate for ballistic drop quickly as well (without needing a spotter to do the match for you for adjustments quickly instead).

Max range on a M-203 is 437 yards, so why are we talking close up range work that a 40mm HE would be the better choice isntead?
Hence it like playing horseshoes, and even getting close in regards to a few feet with a HE is good enough instead.

As for distance, it all about where the round is going to slow down to around mach 1.2, and where the wheels fall off as the bullet comes out of sleep.