Also...

by rob , Sunday, November 24, 2013, 09:07 (4022 days ago) @ rob

You asked about rifles and I forgot to mention it. In a pistol caliber rifle like .357, .44, etc. there really is no forcing cone, just a lead into the rifling. What causes the erosion is the hot powder gasses in the tapered forcing cone surrounding the bullet while waiting for it to pass into the bore where it then strictly pushes from behind and passes through...not very eloquent but it's the best way I know how to explain it. Even in magnum rifle rounds with slow powders most of the powder is burned in the first 3-4" and then it's expanding gas pushing on the bullet. So, in a handgun round like .357, even with the slowest of powders, it's pretty much burned by the time it passes the forcing cone. In a revolver, longer heavier bullets like the .180's in a .357 tend to mitigate the effects of forcing cone erosion while the shorter lighter 125's tend to intensify the effect. Also, in bottleneck rifles, supposedly using boat tail bullets extensively causes it as well for the same reason as the forcing cone in a revolver,,,you have a tapered area around the base of the bullet with burning powder rather than behind it. That's my amateur analysis anyhow. Some of the smarter engineer types on here like Glen might be able to explain it better or correct my laid back country boy redneckefied way of 'splaining it:)