<I dont mean to step on your neck here .. but the load in discussion is a 300 grain baseball sized chuck of lead over titegroup ....
this is getting fairly extreme as combinations go.>

Good grief.........don't be such a drama queen. I'm not passing judgement on the practicality of the OP's choice of bullet weight for plinking. His 300gr. bullet may be quite accurate in his gun. Since you don't know how much bullet nose sits out past the cannelure, you don't really know much case is available for the powder charge. A 300gr. bullet clocking under 1000 fps isn't going to be any more of a handful than a typical 240gr. bullet clocking 1300 in the 44Mag.

Roundgunner.............I load 45Colt with 6.2 grains of Titegroup under a 255gr. lswc. This load clocks 825 fps in a 5" 625-5. Your loading seems to produce results similar to mine. Amazingly, I get a velocity spread of 12-15fps with this recipe that prints one-hole groups at 25 yds. This is with a case that can be filled with three times as much of a slower powder............Amazing indeed!