Conman: The ratcatcher

[Sir_SwampThing]

It was claimed it was a few weeks in the add. I received it and it is 4 Months old.

If you know it is 4 months old, that suggests that you have either got the original receipt or the shop have confirmed when it was purchased.
So I would be negotiating (without accusations) with both the shop manager and Brocock to either drive to the store (or have it returned) so that they can at least advise you what the issue is. However, based on the title of this thread, I suspect that you may have already burned your bridges with the store.
Because, unfortunately, you don't stand a cat in hells chance of success in either a police claim (not going to happen) or a civil case, because unless the gun was received physically damaged (and immediately recorded/evidenced as such) you just cannot prove your case (or that you have not tampered with it yourself).

Atb
Chris