Chalk that up to a big difference in rifle specs. Like you said tighter bore maybe different chamber, etc.....
When I started w/the old girl back in 1966 I stuck it full of 4831 (60 grains - compressed load) O'Connor and Speer said 3100 FPS.
It shot 2/4" and I shot a lot of deer with with that load.
Then I bought on of the first Oehler chrono's. Velocity was comparable to yours. Being a velocity hog I switched to N205 which would push it right at 3190 in the summer.
N205 went away and I had to switch to 4350 to get the same velocity. Pressures were very high but not 'real' sticky.
Then along comes RL-22 (same as but fewer quality controls than Norma205 or MRP, I think)
Now I have the best of both worlds. Decent pressure, good accuracy, long case life. However, it is a bit temperature sensitive.
+ its a 27" barrel.