Thanks again for the replies so far fellas.

What most of you have talked about is exactly what I have been doing with my rifles for the last 20 years - remove all copper and carbon fouling periodically, dry, then oil. It had seemed like a winning formula and is certainly something that I have and will continue to apply in my bolt and single shot rifles.

I will likely take up my gunsmith friends kind offer to come and have a look through a borescope at a couple of double guns, he is of the opinion that the fouling in a double tends to be a reasonably good thing and that cleaning back to steel is unecessary and has the potential to decrease accuracy.

I understand the various viewpoints on this, they have all have good degrees of merit and every rifle is a law unto itself, but this particular 'smith is a regular shooter and repairer of doubles so I tend to hold his opinion in high regard.

I also note though that in reality, the differences in accuracy we are talking about when considering large bore rifles, either positive or negative, are unlikely to be of any significant consequence. I guess as long as I can continue to group both barrels into the size of an orange at the right distance and point of aim, then it is a bit hard to complain.