Evening all.
OK, had a quick look tonight and it was the magazine indexing screw. Just followed the instructions in the Steyr service video, and job done and I'm a little bit wiser now with the H5. Shame there aren't more service videos on the H5 but hopefully I won't need anymore anyway!
I have to say part of the reason I have three Steyrs is the ease of maintenance, partly due to the service videos.
Thanks for the steer Tinbum and Rich (should have gone straight therein the first place).
Steyr Challenge HFT - HW97K - BSA Mercury Challenger - Anschutz 9015 One - AA Pro Target - AA Pro Elite - ASI Paratrooper (R) - Walther LP500