in 1990, I put a leupold 3.5-20 on a 7T Colt H bar that I had re worked the trigger to make it lighter. Worked up a good load with a 55g Sierra HPBT with AA2460 that shot 1/2". I loaded the same bullet in a 22/250 Shilen 14T at 3600.
I had 17 of the 30 round clips and 12 of the twenty round clips. I Found a p. dog town around Valentine, Nb that was 13 miles long and 3.5 miles wide, no way to get to it but drive across the prairie. We started hammering the dogs, I of course was blazing away with the H bar. I noticed that the 55g Sierra BTHP at 300 yards was making the p. dogs fly in the air, and not so much with the 22/250 going 600 fps faster...learned a thing or two on that trip.
Bullet jackets seem to have a certain amount of rotational torque(and the base) before they explode. It did not take much for the H bar round to detonate a p. dog.
My next lesson was on a 223 with a 9Twist and zero freebore, I had the same reamer used on two Hart barrels, on 9T and another 14T, zero freebore. I noticed the 9T blew up dogs better. So, I had a custom Sako A1 built, as a repeater, 9T Hart barrel, in a McMillen Sako varmint stock, 22 ppc-9T, zero freebore. The 9T in the 223 and 22 PPC both blew up dogs better than their 14T counter parts, but the tune window on the load was much more narrow and susceptible to more changes in weather.
I think that if you want to shoot heavies, throat for heavies and shoot heavies. If you want to shoot light bullets, go for the proper twist and throat very short.
Maybe a .0003+ over bullet dia throat would help with longer freebore, then again, the reamer makers have a .0005 +/- on dimensions that they allow on a dimension...better trust your reamer maker....