Gosh darn it what does LBT mean when it comes to bullet composition? Specifically 44 magnum ammo?

I've been wondering for months if not years now. I know all the other freakin initials for ammo make up but I have no idea what in tarnation LBT means.

It shouldn't be Lead Ballistic Tip or Lead Boat Tail, neither of those really make sense. The pictures appear to be standard Lead Flat Nose so there's no clues there.

Please...someone, I am sick as a dog and passing the time shopping for gun stuff and this is really frustrating me.