I’ve been wondering about the difference between a new 308 barrel and some older 308 barrels.
The older ones each have 3000 to 5000 rounds through them.
They also do better with some of my 308 loads. i.e. the new barrel is getting over-pressure, with bullets that were AOK in the older rifles.
It’s as if the new barrel has a slightly smaller diameter, like .0001 smaller.
Has anybody ever heard about how much erosion is caused on a steel barrel when a copper jacketed bullet is fired from it ?
From experience machining, I know that softer metals can cause wear in steel. When the steel cutter meets the aluminum or copper block, the steel usually wins - but the steel still wears. i.e. material is worn away.
Let’s say every time you fire a copper-jacketed bullet, it wears 0.000,000,1 inches off the inside of the steel barrel.
That’s 1/10 of 1/ millionth of an inch, per bullet.
So after 3000 bullets, the diameter may be altered by .0003 inches.
Or maybe it wears 1/100 of 1/ millionth of an inch.
Alternately … maybe the new barrel is just a tiny bit smaller diameter than the older barrels.
I havent, and i have no idea how much wear occurs even every 1000 rounds. these are some serious questions that id think the manufacturers would have answers for when they were developing the barrels to begin with. I could be wrong there but im just not sure. That is some serious in depth questions that im sure the answers are out there somewhere. i’ve just never thought about it nor researched it.
sorry i cannot be much help.
Throat wear is a bigger concern than the rifling [in regards to accuracy] - all wear rate is likely almost-impossible to quantify due to differences in metallurgy/surface finish/hardness from one barrel to another, even in the same batch - or powder/primer type and charge [corrosiveness], bullet type/composition, or even rate of fire (mag dumps heat a barrel up quickly, and sustained heat DOES have a negative influence on metal strength)
Youtube channel Gunblue490 has an excellent presentation on the subject of barrel longevity.
1 - SAAMI specifies a minimum area for the bore and groove geometry. There can be susbtantian variations in the geomerty of the barrel cross section as between manufacturers and tooling makers
2 On firing you are subjecting the surface of the barrel to temperatures exceeding the melting point of the steel and pressures as high as 60,000 PSI and turbulent supersonic gas flow (think plasma cutter). That is the mechanism that destroys barrels.