After reading lots of arguments pro and con, and admitting I am not an expert; I'll go out on a limb here (feel free to follow me with a saw).
I would say that a musket or rifle of the same operating mechanism as an original (no coil springs, 209 conversions, etc), with an appropriate finish on wood and metal (no anodized or parkerized metal, or polyurethane wood), with the approximately proper proportions and measurements of an original model, or similar proportions and measurements of a notable style of gun (ie Hawken, English fowler, Penn rifle, Barn gun) should fit the bill of PC.
I'm thinking that if a knowledgeable person can look at it and recognize the model or style immediately (as in "hey, that's a 1795 Springfield musket, right?", or " what's the finish on your Hawken?"), then you have a gun that, while not perfect, should be considered PC.
I've heard that some Bess's from india are too chunky, but you do recognize them immediately for what they are copying.
As for me... I do not shoot or own "custom rifles". My finances won't allow it, or $500 clothing from professional sutlers.
I have a good time with my NOT PC Traditions Hawken Woodsman, a pair of homemade mocassins, and a shirt of cotton under a wool balnket shirt (all handmade 'ceptin the rifle)over a pair of REALLY NOT PC canvas pants (storebought).
So I guess it's how authentic do you want to be?
Do you want to simulate the period and have some fun, or spend every moment documenting and procuring A#1 authentic one of a kind equipment while going nuts counting threads and watching your bank account dwindle.
I'm in this for a cheap, fun hobby and to learn a thing or two....if it's PC enough for me, then it's PC enough...
Just an opinion....
Legion