Vapor trial

[Wrangler John]

Well, my theory is that the thin jacket soft lead core bullets do not support the core sufficiently, and are damaged from rifling engraving - which becomes stress risers depending on rifling depth and form. Couple that with the high temperatures mentioned by Fred C Dobbs, the core becomes plastic and centrifugal force tears things apart. High velocity = heat from powder charge + friction. The barrels used on these rifles were 1:12" twist.

As I mentioned in my first post, powdered metal core lead free bullets seem to immune from this phenomena, as does the monolithic copper bullet such as the Barnes TTSX. Although excessive pressure has destroyed certain powdered metal core bullets, this breakup occurs as the bullet exits the muzzle. It is confirmed by the usual signs of sticky bolt lift and anomalous chronograph readings (5,000+/- fps) for the fragments. Cut rifling also seems to more readily produce the failure.

One observation is that polygonal rifling seems to provide a bit more accuracy with some of the smaller calibers while reducing pressures. Maybe it also is kinder on the bullet, I know some 1000 yard match shooters use that form exclusively. As my barrel budget warrants, I really want to try more of this rifling form. The .223 Remington really came alive for me with Nosler's 40 grain BT Lead Free in a 1:9" polygonal barrel.