2250 power mods

i realize this has probabaly been posted to death. but rather than google search a thousand posts dating back ten or more years, i thought i'd be up front...



hey y'all....once again, i have a little time on my hands to tinker. since i now have a new "gopher" population mining in my yard, i wanted to build something that will take them out quickly and quietly.
figured I'd use the the 14" barreled 2250 carbine that's been gathering dust in the safe.

so here are the parameters:
1.range will generally be 25 yards or less.
2.pellets will be either jsb 15.9s or 16 gr predators.
3.power will remain 12g co2 cartridges
4. shot count is NOT an issue
5. ideally, id like to see 650-700fps
6. temp is not an issue ( 82degrees here today in winter )

with that said, what recommendations does the forum make ? I'd guess most would be in valve work, and to that end I'll likely spring for a b&a boss valve and add the poly transfer mod.

the trigger has already been reworked and breaks at a crisp, creepfree 2#s.
barrel has been nicely crowned and a long steel breech makes a great platform to mount optics.

so what would y'all recommend to get some oomph outta this little gas gun ?