It's simply what SC928 said. The milsurp load is optimized for the much more common 28-3/4" (or thereabouts) barrel of the 91/30 and it's variants.
In the shorter carbine barrel, you have excessive powder still burning as the exhaust gases exit the barrel behind the bullet.
Far as handloads, it's basically a .308, though because of more case capacity (8 more gr H20) it can be loaded close to the .06. Most of us that shoot handloads for precision find that when approaching max loads accuracy deteriorates.
However, my long range handload is 43.5 of Varget and the 174 grain SMK...
exactly that of my son's .308 Savage, but with the 175 SMK.
Unfortunately, the 174 SMK is the only game in town when it comes to .311 match grade boolits. If only Berger made a VLD... it could be interesting.