blue: 45 gns of 4895 is a listed accuracy load that should get the 150 gn bullet moving at about 2770'/sec, at 50k cup. That's a max loading for 4895.
If you are concerned about an oversized chamber then get some Cerrosafe (er whatever) and mic out your chamber.
I seem to recall 7.62x51mm Match/Sniper loadings using a 173 gn slug at 2550'/sec, so you're not looking to set any speed records but rather develop safe, accurate loads.
HTH. Mikey.