My Browning gets wild when the barrel warms up also. BTW, mine is a LH model, too, but not stainless.
I gave it plenty of time to cool off, and loaded an extra round to get my first shot flyer out of the way. It just didn't shoot, which has never happened with this rifle in the last 12 years I've owned it. That is part of the reason I am shocked with the results.
I think I'm going to try out some Sierras using my current powder, and then if I have problems after that, I'll go to new powders. The 4831 is something I'd like to stick with if I can, because I get EXCEPTIONAL results with it in my 7mm Mag and I would like to keep them shooting the same powder if possible, but will change out if I have to.