Originally Posted by Loner
One of the later theories is that granular powders being pushed into the throat
by the explosion at the back of the case do some eroding and of coarse are burned
there as well. Putting a primer tube in the case so it ignites the powder from the
neck first lengthened throat life so it seemed testing bore it out. You have a cartridge
that is going to produce about 600-800 rounds before the throat erodes enough
for you to notice a change in accuracy. Keeping your loads backed off from maximum
will do more to insure that than powder choice in my opinion.
with smokeless powder there is no explosion like there is with black powder. The bullet moves via pneumatics. But then there is a much higher concentration of heat build up verses the older stuff. You take that into fact along with much larger amounts of powder, and you are ending up with a flame that is higher than the melting point of the steel itself. A 40 degree shoulder will help fight off barrel errosion assuming there is an ample amount of neck length to contain the vortex of the flame inside the neck instead of ending up in the throat like some many short necked cartridges are. Ideally you want the vortex of the flame in the first half of the neck (furthest away from the throat). A typical Weatherby case will compute out at about 48 degrees by the way.
As for backing off the loading on a 378 case; that can be a very bad thing! Those big cases don't like this, and are at their best at near max loads