It is the third largest/lowest sprocket on the cassette of a ten speed sram cassette. Bizzarely when I am in that gear it just not want to sit still, it just jumps and skips all the while. It is also fine across the rest of the range.

It is certainly not a worn chain/sprocket issue as they were all new together (cassette, chain, chainring and mech).

Running a sram chain (10spd), cassette (11-36 10 speed), e13 guidering (34) and a x9 type 2 mech.

Any ideas on what could be the cause?

Have you checked there’s not a bent tooth on the gear it jumps in?

I’d say either a bent/mishaped tooth or possible gears are not indexed correctly.

Have you removed the cassette recently? If so, have you put the ring on the wrong way round?

You can’t remove the third largest sprocket (without getting medieval with it’s @rse )

Assuming by “large” the OP meant size.

Not familiar with this specific cassette as I’m a Shimano man, but have you missed a spacer when reinstalling it?

Spacer was a no, it is on the spider the gear that I was skipping.

Large was size, lowest by ratio.

Just had a look and I have bent the second largest/lowest sprocket outwards just near the pick up on the cassette, hence it was jumping into that gear then back down again. New cassette for me!

I’ve seen heaps of Sram cassettes with some of the larger sprockets buckled. pedal back slowly (with chain on another sprocket) and see what you find.

Cassette sprockets are so thin these days I’m surprised this isn’t more common.

Bend it back.

Just had a look and I have bent the second largest/lowest sprocket outwards just near the pick up on the cassette, hence it was jumping into that gear then back down again. New cassette Pair of pliers for me!

Fixed it innit…

I have tried bending it back using leverage from allen keys, pliers, files etc. Also some percussive maintenance. It’s good and proper stuck. Just going to get a new cassette, no need for me to get smacking it anymore than I have.