I put a new chain (the third) on this cassette at the weekend and it’s skipping in the middle of the block. I’m pretty sure the indexing/set up is OK, tho I did change the cable at the same time too.

It’s a SRAM 10 speed chain on a SRAM 10 speed cassette.

Is the cassette worn out (in which case I’ll put the second chain back on and run it to death), or is it something else?

Ta.

If it’s slipping I’d say yes, the 6th, 7th and 8th sprockets do look a bit worn.

5 – 6 – 7 look shot to me

put a new cassette on and see if it fixes it. If it does, then yes it’s knackered. Then you can swap back and run it to death as you say.

But be aware that in doing that you might also knacker the front chainring(s) and thus need to change them as well. In fact – worth running the new cassette and chain first to see if it still slips, maybe it’s the front that’s causing the issue.

Cassettes wear in a shark’s tooth shape. Sounds likely.

If you run a stretched chain then the cassette (and chain rings) will wear and a new chain will jump about and slip.

Thx folks.