I was here a while back asking about 500 s&w load data, among other questions. I've not been able to find good data on 4" velocities vs the 8 3/8, which most factory ammo seems to be tested with. My curiosity got the better of me, and i decided to get a chrono.
So far, i've been starting on the light side, and working my way up with mostly Hornady 300gr FTX bullet. My thinking is that since i'm in PA, this size should take down any game, and give me a pretty flat shooting round at higher velocities, as well as keep recoil tolerable.
I used load data for H110, which is my powder of choice for the 500, and hogdon lists this for 325 grain (no listing for 300) so i assume it would be a safe range for 300 grain
Bullet Powder OAL Start Vel Pressure Max Velocity Pressure
325 GR. BAR XPB Hodgdon H110 2.290" 42.0 1813 40,000 PSI 45.3 1951 48,900 PSI
By looking at the listed velocity on these Hornady factory loads and chronographing them in my gun, my best guess is the 4" loses about 275-350 fps over the 8 3/8 barrel for this cartridge. However i can't be sure because i cannot validate the hornady claim of 2050 fps from a 8 3/8
I'm looking to push the 300 to the same velocity as the above hornady factory ammo, which chronographed about 1700 fps for me. Below is the chart showing what i'm loaded and chronographed already, and what my plans are. 51.4 grains of H110 seems like quite a bit for a 300 grain bullet, but its what hornady is recomending, and i validated the chart by calling hornady. The velocity listed in the hornady PDF below is from a 8 3/8 of course.
I also tested the 500 grain XTP over 32.0 grains of H110, which i'm quite happy with. Muzzle energy isn't phenomenal, but its about all the recoil i want to deal with. Should make a good bear round.