Thanks Steve,

that's a big help. Thanks for clearing that up for me. I read Frank DeHaas' book and he suggests the BRNO action is based on the M98 but doesn't mention any thread difference. He also doesn't show a separate barrel stub drawing for the BRNO like he does for the other M98 derivatives so I wasn't sure.

I'm making inquiries with a barrel distributor at the moment and yes, he did mention the extra cost for a non shelf item (M98 thread) barrel. I'm just trying to find a profile now that will match the factory ZKK 600 barrel close enough to use the factory stock.

If Lothar Walther don't cut the ZKK thread I'll have a chat to the gunsmith when he gets back from holidays about cutting the threads to suit if I order an un-threaded barrel stub as you suggest.

Apologies again for the off topic thread dig everyone. Hopefully it will help someone taking on a similar project.

Cheers
Darren