RE: 3030 improved
I have to agree with the others, I see no reason to change what is already a good 200 yard chambering.
I reload for my Marlin 336 30-30 using 150gr Win round nose bullets and 35gr of IMR3031. That load gives me a 1.75" 10 shot group at 100 yards any time Ishoot it. It clocks right at 2500fps and I dropped a nice bodyed young buck this year with it at 160 yards. My gun only has a 20" barrel, with a longer barrel it should be a little faster. I'm looking forward to Hornady's releasing the new pointed bullet mentioned earlier which looks like it could extend the effective range of this old cartridge by up to 100 yards or more.
If you reload for your gun you would not be limited to the standard 30-30 fare. If this is the case you could use whatever pointed/boat tail design bullet you want to achieve the desired results using the chamber you already have. If you don't reload, I would put theupgrade money into reloading gear instead.
Good luck and let us know what you end up doing.