what is it that causes throat erosion? velocity of bullet or large case of powder? I am currently working on loads for a 300 rum and was wondering if loading 220gr Sierra Match King bullets would extend the life of the barrel as compared to 190gr Sierra Match King.
does anyone know the rate of twist in a Sendero 300 RUM? would the 240gr Match King work in this rifle?
300 RUM and a 458 win mag...what more can a man want!
The twist on the factory Sendero barrels is 1:10. I've never shot the 240 gr SMK in mine.My bullet of choice is the 220 SMK and it gives great results. I can't say if it will cause more throat erosion then the 190 SMK though. I've always been under the impression that erosion is a function of heat and pressure. Seat the bullet as close as you can to the lands and keeping the barrel cool and clean will go a long way to keep erosion to a minimum.
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.
I think alot has to do with the size of the powder grains, with the majority of powder still un-burnt at the throat its all hitting the barrel at high velocities causing a sand blasting effect, with the larger grains hitting with more force thus causing more errosion, As varmint hunter said light charges=less errosion it is because more powder is being burnt in the case and less hitting the throat. As for heavy bullets causing more wear, its probably because those people are using slow powder, and slow powder is usally larger grain. I think bullets have an almost zero effect on throat errosion, if bullets caused all the errosion, the barrel would wear at the middle/end, causing that part to go before the throat.