IIRC LC stands for Long Reach on OS plugs and the plug is longer, and goes further into the head, causing actual higher compression from less volume in the chamber.
I tried a LC4 in my Axial .28 a while back and I just tore it down before installing in my Savage, found detonation, and the plug protrudes waay too far into the button.
I won't be running that plug anymore.