Keith Skjerdal
Member
Yet another erosion variable, the design of base of the bullet. I "think" BT, VLD's and rebated bullets erode more than flat base bullets since the gas is directed into the rifling, JMO.
sherrett....why does a benchrest barrel lose accuracy between cleanings
If a barrel lost accuracy between cleaning, then you should get the best accuracy by cleaning between each shot. Ive tried this - doesn't seem to work.
Sherrett...will this additional fouling reduce or increase barrel erosion
Depends on what the fowling is - soft fowling might act as lubricant, while hard fowling might act as abrasive. Fowling coating the bore might protect it and prevent wear
skjerdal....the gas is directed into the rifling...
The gas at the base of the bullet is not flowing into or against the boat tail bevel. It's essentially just moving along the bore with the bullet. As a matter of fact, relative to the base of the bullet, the gas is flowing away from this point as it expands when the pressure drops in the bore.The shape of the base of the bullet would have little, or no, effect on gas velocity at this point, and thus no effect on wear or erosion.
If a barrel lost accuracy between cleaning, then you should get the best accuracy by cleaning between each shot. Ive tried this - doesn't seem to work.
Sherrett...will this additional fouling reduce or increase barrel erosion
Depends on what the fowling is - soft fowling might act as lubricant, while hard fowling might act as abrasive. Fowling coating the bore might protect it and prevent wear
skjerdal....the gas is directed into the rifling...
The gas at the base of the bullet is not flowing into or against the boat tail bevel. It's essentially just moving along the bore with the bullet. As a matter of fact, relative to the base of the bullet, the gas is flowing away from this point as it expands when the pressure drops in the bore.The shape of the base of the bullet would have little, or no, effect on gas velocity at this point, and thus no effect on wear or erosion.
JerrySharrett
Senile Member
Most ill informed answers I've seen in a while!!!
Benchrest shooters know for sure that cleaning after each shot will not work. A barrel doesn't attain its peak accuracy until it ahs been shot a few times. And they know that a benchrest quality barrel will loose its peak accuracy, depending on the barrel, after several shots.
Hard foulding and soft fouling, I didn't realize we had a choice????
Keith Skjerdal
Member
It all happens in a milliseconds and you know this thru physics and fluid tests, right, so, only if you say so LOL
Boyd Allen
Active member
As far as I know, CF barrels do not wear out, they burn out. Heat causes a thin carburized layer, at and near the throat. Combustion pressure causes the underlying steel to stretch, and carburized layer , being less flexible and more glass like, cracks. and gas erosion starts along those cracks, causing them to become enlarged, and eventually chunks of the bore surface are lost. This surface roughening causes fouling issues, that eventually cause accuracy to become unacceptable. All of this takes place long before wear due to sliding friction would become a problem.
F
frwillia
Guest
That's pretty much how I understand it.
Looking in the chamber throat of my .22-250 (Savage LRPV) after about 2,500 rounds, it looked like a dry lake bed. The surface had shrunk relative to the deeper (.002" to .003") and created what looked for all the world like scales. The way these are formed, the hot gasses heat a very thin layer of metal to red hot extremely quickly, the red hot metal both expands and compresses, and when it cools, it shrinks. The gasses are so hot they can transfer heat to the first few thousandts of metal depth much faster than the metal can conduct it away to the underlying metal mass of the barrel. The surface to underlying metal temperature gradient is huge, but very short, so the relative expansion difference is also huge, then it cools rather quickly as the hot gasses vanish with the bullet leaving the bore. The first shot starts the process, as the shots count up, the repeated expansion and contraction will eventually cause micro cracks that expand leaving the scale like appearance - thermal cycle fatigue on the surface. My .22-250 had the scales for a good 1-1/2" past the throat with less severe thermal erosion effects for another several inches. The rest of the bore looked increasingly like new to about the half way point of the barrel and the rest of it looked quite good.
I didn't have the ability to take pictures through the borescope when I set the barrel back 2" or I'd post them here. It really did look like a nasty black micro version of a dry lake bed with the typical cracked and scaled mud.
Fitch