I'm going to try my best to answer the original question. By plinking load, I am assuming you mean an 800-1000 fps load. Double check with Hodgdon's data and use the data for the 325 cast if they don't list a 300 cast. You should find a working load between 7.0-8.0 grs of Titegroup. If your bullet has two crimp grooves use the longest OAL that will fit in your sixgun. BE CAREFUL!!!!!

Now, that being said, I have worked a good bit with TG, Bullseye, Red Dot and other really fast burning powders in the 44 Mag and Heavy 45 Colt with 300-325 cast bullets. Can you make a plinking load yes. Based on my direct experience, I would STRONGLY recommend going to a medium burn speed powder. You won't need 2400, No. 9 or other slower speed powders and in fact they only seem to work best at higher pressures (closer to full power loads).

The sweet spot for me was around 800-950 fps loads with medium speed powders like Unique, Universal, Power Pistol, No. 5, and HS-6. These won't be cowboy action light loads, but are very reasonable pressure-wise. Your Sixgun and you will readily digest a ton of them and they are pleasent to shoot (not all the muzzle blast like the slow powders). You will also find that the medium speed powders burn VERY cleanly with the resistance offered by the 300 grn bullets and the recoil isn't too bad. More of a slow push than and snap. Based on what I experienced, I don't think the super fast burning powders and really heavy for caliber bullets are a good match. The pressure curve is really steep and there is little margin for error. Remember the axiom: Just becasue you can, doesn't mean you should.

What I found was that the upper end of this range 900-950 fps make great field loads. Remember the cowboys used to kill plenty of animals and bandits with a 250 gr bullets at this same speed in their 45 Colts. You will have plenty more thump with your 300's.

Get you a 1 lb. can of a mid speed powder and work up. I think you will be very happy.

Good Luck,
Mark in GA