Ermagerd!
Think it's resolved!
Haven't played a raid yet but I'm in my inventory, collected insurance and hideout stuff - all good so far.
Just after my last post I tried editing my profile again.
I found and deleted every reference to 53a4d16f55904fe56c9f57f1 which was the object it was complaining about in the original dialogue.
There were a lot of them, presumably for the mag itself and every round inside it. I'm sure your way is more elegant!
Tried it before but it broke my profile.
In case it helps anyone in the future here's what I think did it:
When deleting sections I was concerned that unexpected blank lines/whitespace might break the parser so when I got rid of a section and there was a blank line I tried to tidy it up.
Don't worry about that, just leave the empty lines etc.
Thought I'd have to revert back to a level 40 backup, not like starting from scratch but between 40 and 45 I bought a lot of containers and reorganised my stash.
Plus now I know about the profile editor so finishing the bugged gunsmith tasks should be a lot less hassle.
Thanks very much for the help, appreciated.