When cores melt in a jacketed bullet, it isn't from gasses. Its the core slipping inside the jacket from rotational load and pressure on the barrel wall.
That's why thin jackets and non-concentric bullet cores go poof when twist gets too steep. Its also the reason fit with cast is so important.
If you don't have full diameter support and a seal or bad barrel conditions the lead moves/slips and under load with barrel friction it exceeds its melting point in those "loose" areas, causing leading. This is why some get leading even from hard alloys and prefer softer ones; there needs to be a seal. The load bearing ability of a harder alloy is going to be greater.
Gas checks help keep these minor areas of poor fit and leading cleaned up and consistent. It also prevents slippage at that most stressed area.
The coated bullets do similar things but most importantly it is lubrication between the bore and lead, especially at the base to bore contact area where pressure and friction from that pressure is greatest.
I really don't use any gas checked stuff in any handguns.
Last edited by HawkI; 01/29/23.
