early flintlock rifles

Hello everyone, Does anyone have any advice on building an "early" flintlock long rifle based on the J.P. Beck kit which Track of the Wolf offers? The reason I ask this is that I would like to have a rifle made with a Colerain American Heritage barrel, and their J.P. Beck Kit looks like it is...

I was wondering if anyone has any insight into when the first rifles which we would call English Sporting Rifles were first made, and what they might have looked like? I have found a few books which might be informative including Neal and Back's "Great British Gunmakers 1740-1790" and I read...