Just so happens that I shot some of these out of my little .45 birds head just a couple days ago as I was spelling my reg Vaquero from the heat & hot guns!.
12.7gr of Bluedot & CCI 350 primers is listed as 900fps for the 300gr in my Sierra manual with a 7-1/2 test gun being used. My birds head is a 4" so you will need to knock some velocity off for that.
The end result was a very plesant to shoot little pop-gun. It was noticibley lighter recoiled than the 18.7gr of 2400 & 250gr XTP's that I was shooting out of my Reg Vaquero.
I fired 18 of those 300gr through the little gun. 6 at 30yds & 12 more at 50yds and ended up with 3 six shot groups that averaged 3". Not too bad! That darn little birds head has been begging me to take it hunting and I chose those loads just for the chance to give it something that it would not like.
Hope that this helps Some.
P.S. My reg 7-1/2" .45 Vaquero with the 18.7gr of 2400 & 250gr XTP's did better than this. The thing is like a killing machine not to be trifled with
I hope it's accuracy will hold on up to 20gr.
