The bolt rig
Even with the softer trace materials and hair rigs, carp were still believed to be mouthing the baits and ejecting them without any indication of a bite. The bolt rig involves having the weight fixed to the line so that the line cannot slide through it. When the carp picks up the bait, it senses something is wrong and panics or bolts. As it does so, it immediately gets resistance from the heavy weight, which causes the hook to penetrate the carps mouth and it is hooked. This is the reason for the so called "screaming runs" we often see today, where the carp is already hooked and racing for the nearest safe haven it can find, meanwhile on the bank it is pulling line from your reel at a vast rate and your bite indicator is screaming.
The problem with fixed weights is that if a carp runs into snags and manages to break your line above the weight, it could end up towing a lead around until it becomes snagged, and if it can't get out of it, then it may stay snagged until it starves to death. To prevent this, anglers use what we call a semi fixed lead, where the lead is trapped to the line by some mechanism, but if it becomes snagged it will pull free. OK so you lose a lead, but that is always preferable to harming and maybe killing a fish.
