ForestHill
Retro Guru
Ah ha! I have plenty of those lying around in the shed but didn't realise they were M4. I spent a good amount of time pulling my hair out, as they seem to be difficult to buy as an "m4 barrel adjuster".
I ended up taking one from a knackered rear mech, but your option is cheaper and easier probably.
I ended up taking one from a knackered rear mech, but your option is cheaper and easier probably.