I regularly tackle buffs with .50 calibers, flying the F6F, using a diving approach if at all possible, from at least 3k above and slightly to one side of buff's line of flight.
A couple of short bursts to correctly establish the correct amount of lead, then hold the trigger down. If I misjudge their speed, and appear to be falling into a trailing position on the 6, which is not where you want to be, I will fire a short burst and then dive through.
I will fly for 10 minutes or longer to set up such a pass, especially if I am alone. I have a fair amount of success against the heavy buffs with these tactics.
Patience, speed, and gunnery appears to be the key to success.