The forums were indeed on britishguns.net and I was one of the people that got them added to the site.

Sadly the site owner passed away a few months ago and the site is no longer maintained. There was talk of it being run by someone new but this has not yet materialised.

There is now a "British Flint and Percussion Arms" forum at http://p223.ezboard.com/bbritishmilitariaforums

Additionally you might also look at the forums on the Research Press web site at http://www.researchpress.co.uk/
These focus primarily on British arms.

David