In reply to Offwidth:
You are right! Sorry about that - I should have been more clear and highlight the dangers and need for a proper system. It's not something anybody without proper understanding of it all should try at home. Unfortunately I cannot edit or delete my post anymore, as it's >30minutes old
Something like this?
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If it's a bit trashed and you are not comfortable using it even for abbing, how about a fall tower [1]? We used somewhat older ropes (ones that were still viable, not core shot, not sheathed, just not good enough for normal use) for it, since they inevitably got trashed in repeated simulated falls. Obviously with a bag of sand, not a live person at the falling end (!) and a well made and safe system - there are many things that could go wrong with a fall tower and big bag of sand, especially with big FF falls, that could seriously injure or kill, a heavy sandbag falling any height has a lot of energy, ropes tend to snap or cut the sheath at such FF with redirects, a hard bag of sand exerts quite higher forces on the ropes and bolts than a softer, same weight "climber" equivalent, et cetera!
Why not ask around local clubs if they have a safe system set up? Different belay styles and devices, can be good training especially for the newbies [2]. It can still be recycled into chalkbags later.
[1]: obviously with a sand bag, not a live climber on the other end of the rope! Old quarry bolted just for that, without any viable routes - do not do it at a crag!
[2]: mind the safety! Wear helmets, redirect well enough - nobody wants a loaded sand bag on a potentially suspect rope coming fast directly at them! Poor bolts flying out, badly loaded crabs, blocks coming loose, et cetera!
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Or mods, could you perhaps please delete it outright? Not wanting to give anybody the wrong idea...
Post edited at 11:00