having the flesh/rough side on the outside is also the way the Indian's and Frontiersman made there's
Not really - all most all of the original rifle scabbards of this type were made from Indian made braintan leather which has no smooth side, both sides are "sueded" because the hair is scraped off and along with it (most) of the smooth grain.
Water absorption - the smooth side will absorb water just about as fast as the flesh side, especially with buckskin or elk hide - this is based on actual testing - the difference is generally in less than a second and it wicks through from one side to the other in a very short time after that dependent on how wet it goods.- good "theory" but unfortunately in my experience it's just that.
On the other hand either side can have a water resistant finish applied. Plain and simply though there is NO guaranteed way of waterproofing leather.....do like the old timers did and keep your guns well oiled and well cleaned when you can.....
As for suede lining - I don't use it either,but as noted above - how many unlined cow hide holsters do ya'll make with the smooth side in? Yep you can smooth the rough side by burnishing, but it really doesn't make a big difference in the long run. No matter what you do, even a good smooth side lining like calfskin will eventually pick up grit, etc. and on "soft' hides like buckskin the smooth side is not that different from the flesh when it comes to picking up grit - it has a much more open grain and is thus quite porous compared to cowhide. Heck even Kydex picks up and gets embedded with grit after a while.
As for being dirty on the inside of the case - I use black powder exclusively when using my "period" guns (except for M1911 and Ruger BH,period guns are the only thing I own/use - including flint locks) and I've just never seen that big a deal about the inside getting dirty. FWIW - my experience includes 1,000's of miles on horseback in all kinds of weather while working/hunting - but then again I consider my guns tools and don't worry about pretty. You can always rinse it out with warm water and let dry to remove most of the grit - I do this on my unlined holsters failry regularly.
Long time holster maker Thad Rybka used to put in his catalog regarding wear on the bluing, etc. - "if you're afraid of wear and tear on your guns leave them in the box."
On the other hand when using commercial tanned buckskin with a smooth side if you want to approach the "look" of the originals, then use the rough side out, but in my experience don't kid yourself into thinking it will add more real protection with the smooth side in.
As always take my thoughts as you will, but IMO the overall difference is negligible in my experience........