Doug,
<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>So those heavy, really long, high ballistic coeffient bullets and the fast twists required to stablize them are the cause of rapid throat errosion.<HR></BLOCKQUOTE>
I'm going to take a somewhat different position on this one and say, there's probably more to do with shoulder angle, neck length, PSI, duration of burn (charge wt), powder burn rate and bore diameter than other things mentioned. A lot of it has been verified and is pretty well accepted, I still have reservations about some of it though.
We're talking throat errosion here, and charge weight and pressure while sand blasting the throat may account for much of this alone. The change in barrel time for a 180gr bullet verses a 240gr bullet is about 1.4 MS verses 1.55 MS (milliseconds) while peak pressure remains between .65 MS and .75 MS in each, don't matter what burn rate, within reason.
I'm guessing, but I would think that the additional dwell time for engraving is very, very minimal, if any longer at all...
The advantage not mentioned, but you burn much less powder too.
I'm fixin to go shoot some 178's with 103gr Retumbo, but the 240's use 10% less...
I'll have to add up the rounds I got through this barrel and measure the errosion again, I've got to have about 200-225 rounds through it so far. Insignificant the last time I measured it.