Not going to wrack my brain on powder burn gasses produced when s cartridge is fired but will say if you only take Nitroglycerin into account it is an inaccurate assumption. What about single base powders?

The throat of the entire inside of a high intensity rifle barrel is the combustion chamber with some powders. Burn rate and volume of powder comes into play but even the slowest powder most is burned in the first few inches of bullet travel which puts the most heat in the first few inches of a barrel. The most pressure is in the first few inches of bullet travel while it is being engraved by the rifling with the highest pressure therefore the hottest portion of the burn being when the beginning of the bore (throat) is exposed to the highest pressure, most efficient burning of the powder. I never hear of a barrel burning out in the last half of a barrel it is in the throat where the highest pressures are and hottest fire from the more efficient burn area of the powder.

Cartridges that burn more powder and higher pressures generate more heat in that critical area, like in the examples NRTP gave of the 308 family. Taking extremes of that family compare the 22-243 and the 358 Winchester. Every bit the bullet moves in the .358 bullet moves increases the burn chamber much more than the .224 bullet of the 22-243. That is what is referred to as expansion ratio, a relation of volume of the chamber as a bullet moves down the barrel. The larger the expansion ratio the faster pressures and efficient burn drops off, part of why we use faster burning powder in a 358 Winchester than a 243

Know the feeling, I passed chemistry when I had to take it but went for electrical instead if chemical for a reason.

Same thing goes for single base powders. Combustion produces gases which build the pressure, pushing the bullet out.

I seriously wonder how 6.5SAUM can have a longer barrel life when it's running like 20 more grains of powder

Okay, so my definition of mole was faulty. But still, the total amount of mass does not change.

PV = nRT

HH, trying to understand this with all the dynamics thrown in is a bit tall, but when viewed statically at a point in time it can be understood without too much pain. The bottom line is that erosion will increase as more gas is released down the bore.

I've seen heat, pressure and erosion mentioned but what about abrasion? Unburnt powder is abrasive and the bullet itself is highly abrasive in the first inch.

Yeah, of course there must be conservation of mass. But the thing I'm trying to demonstrate is that solids and gases behave very differently, and when you're converting a solid into a gas, either by reaction or physical change, there can be some very drastic changes in what happens. \



Yeah, I'm in agreement with that point. It just doesn't relate to the ideal gas law.

HWY is on the right track. Throat erosion is caused by several things: heat, pressure, twist rate, velocity, powder burn rate, bearing surface of the bullet, calendar proximity to the vernal equinox, etc. Generally, you can just assume that the more powder a given bore diameter takes, the shorter the barrel life.

I still can't see how 6.5SAUM has such a reportedly long barrel life. Some people are claiming it makes it over 1000 more than even the CM. Maybe Chad or JG would like to chime in here with their experience?

I agree with most of that. The more I think about the ideal gas law in this context, the more complex it becomes trying to relate it to internal ballistics in general.

I questioned/wondered that also, why wouldn't a 6.5 WSM have similar barrel life. The only explanation I ever read was "because"

Funny you mention it. Myself and a couple partners in crime are investigating the 6.5 SAUM. I'm thinking if building one just for shooting matches. It is hard for me to wrap my head around a 140 gr. Berger Hybrid making 3000 fps MV, yet, not eroding a throat in 1000 rounds. It may take more than a year for me to put 1k down the barrel, but when I do, I will be sure to report what erosion I find. We're going to chamber it with zero free bore, so I can chase lands IF the rifle and load want me to chase lands. It will be virgin ground I am personally plowing, but I'm liking the external ballistics I'm seeing with that BC and that MV. It should cut .2 MIL off my 5 mph wind hold out to 1300 yards, against the 6.5 Creedmoor. But is that at the expense of a barrel every 1000 to 1500 rounds? I don't know, I'll just have to shoot the heck out of it, and see what I see.

Don't worry, new barrels re being made as I type.

You and Judd, I swear!

Gunsmiths gotta eat too.

Couldn't a fellow get close to about 3000 fps with a 140 gr bullet in a 6.5-06 AI (or A Square) or a 6.5 Rem Mag? If so, less powder and less erosion. But maybe the 6.5 SAUM is a short action round (I don't have the info in front of me), but if so would the action length really make that much difference?

I think the SAUM falls into case geometry as well but no certainty. My thing is that they claim the life in the 6.5 but the 7mm version is less which is oposite of the rest when going up or down in bore.


Here's the thing to keep in mind that one is popular in f class and a 1/2 min gun might not be ok to those guys but good to a prs or hunter.

That's what's puzzling. Judd told me last weekend he knows of a smith that is a big F-class builder and shooter, that won't ever chamber another 6.5 SAUM because of something like you mentioned. I have no interest in shooting groups, so if it will put 5 in 1" at 500 I'm good with it. G7 .311, MV 3000 fps is salty. It will come down to wind reading and proper correction, as usual. 1/2 MOA from 100 to 1000 is very small in my world.