Years ago I cataloged 400-odd original flintlock rifles from published sources. The average caliber for everything was 0.495. When I narrowed that down to rifles ascribed to the pre-Revolutionary period and Lancaster Co., assuming Lancaster was somewhat early, the average floats up to 0.515. Pre-Revolutionary-only rifles averaged 0.535.
The problem is that we don't know how many of those rifles were repeatedly freshed out until they weren't considered worth the expense of re-working, or how many of them were rebored and re-rifled to make shooters out of them back in the earlier 20th century before reproductions were commonly available. The point of narrowing the sample size to guns out of European collections is that they appear to have been Rev-war trophies that were taken back and preserved, at least as far as bore size, as they were when more or less new.
I used to believe that pre-Rev rifles were almost all .50 or above until I started looking at those well-preserved rifles with known histories and realized that not only were sub-.50 calibers common, the ranges shown matched period accounts pretty well. It is one of the few areas where I think that the really early researchers, Dillon and the like, actually got it about right - the American rifles were distinctively smaller in the bore than were European rifles.
There is a tendency for people today to used as light equipment as they can (.223 for deer, .410 for grouse, pistols for bear, etc.). But if you are truly remote from assistance and playing for keeps, the old adage of "carry enough gun" rings true. I think the sensible vote would be for a minimum of 0.54 cal.
My impression is exactly the opposite - previous generations well into the 20th century were quite happy with calibers and cartridges that are now considered marginally adequate. They didn't have a gun industry that needed to market their latest Ripper-Claw Xtra-Maim bullet to keep abreast of the competition, didn't have hunting ethics that stressed an instantaneous kill (see Meshach Browning, for example), didn't have modern regulations limiting the tactics they could use (running deer with dogs, jacklighting, etc), and had a lot more familiarity with the outdoors, tracking and wildlife behavior, and their firearms than the average hunter today.
I've seen serious arguments that .30-30 is too light for whitetails, and we are all familiar with the belief that roundballs can't kill anything cleanly. Both statements would have been considered preposterous to the generations that used them quite effectively. I think it was sometime after World War II that hunters got magnumitis, as I've read older books commenting on the phenomenon.
On a more general note:
1) Longhunters WERE farmers who were hunting as a side-gig during the off-season. As far as I know, they were not professional, full-time hunters. Boone's year-plus hunt was as long as it was because it was a disaster and he was trying to salvage something from the ruins.
2) The longhunting period was during a long stretch of peace, and while the longhunters were trespassing and poaching, they could reasonably expect not to have to engage in a serious fight. As a matter of fact, the Shawnee and Cherokee do seem to have been pretty lenient when they caught up with Boone's party. Perhaps we are in danger of overemphasizing the possibility of getting into a shooting scrape while out killing deer.
3) Putting together the necessary supplies for a long hunt was costly, and it WAS possible to borrow money to do so. As a matter of fact virtually everyone, both white and Indian, was already in debt and looking to get out, which was probably one of the motivations for doing a long hunt in the first place (and, while I've never seen it mentioned anywhere, the probability of pre-existing debt and debt incurred for the expedition itself also explains why Boone was so desperate to salvage something from the wreck of his venture). Longhunters could have acquired whatever guns they needed, if they didn't already have them.
4) There is a story going around that Boone used a 16-bore while out in Kentucky, but I don't know the source. It isn't from the Nathan Boone interviews, for sure.
Edited to add:
Another good reason to be careful using averages of surviving rifles is that the published caliber measurements may not be accurate. I've seen a number of instances where re-examination gives a different number than older published works, and the bore size always seems to go
down, not up. A lot of this is because rifles are often coned or funneled at the muzzle, so measurements taken right at the muzzle are a little oversized. Also, Shumway did his examinations and photographs in a room that was poorly lit, according to the people who were around at the time, so he missed some things from time to time, like rifling in "smoothbores" that ended before the muzzle. Measuring caliber is a rather more difficult endeavor than one might expect, too, and I think that people tend to overestimate a bit.
I'd subtract about .02" from any average based on Shumway and Kindig, at a guess.
