somewhere i have also a entry about shoot bear with this rifle . im still looking , its been along time since i looked through these
but this will do in the mean time .
now that im thinking and looking it may have been a mention of shooting a bear with this rifle so it may not have been a grizzly
http://www.lewis-clark.org/content/content-article.asp?ArticleID=2355
Another experience recounted in the journals emphasizes that Clark’s favorite rifle had too small a bore to make it reliable for big game shooting. August 8,1804 (from the diary of John Ordway): "the Capt. [Clark] Shot Several times at one [elk] but his rifle carried a Small Ball, took 2 men went to hunt it and he did not Git it." Again, on August 24, 1804, Clark mentioned that in addition to killing two bull elk that evening he wounded two others, but could not track them by blood drops because "my ball was So [too] Small to bleed them well."
I would also add to this that Clark provided an entry on Dec 1oth 1805 here he state the rifle to be the size of 100 to the pound .
This would put this rifle .36 cal as a 45 cal is 60 to the lb
Another thing on these rifles that only a small % were Harpers ferry “15” the rest were muskets fusils and rifles .
We also know That the men from Kentucky brought their own rifles which were long rifles .
If we are to then believe Charles Edward Chapple “fire arms historian “
These rifles would be 45 cal or less , carrying barrels of 40 inches with 6 to 8 groves
Also if we understand the C of D historians the only heavy caliber weapons carried would have been muskets the rest being 54 or smaller and were prefered for hunting over the muskets
So I think we must accept that most likely the rifles used were of much smaller calibers then we think
myself regularly shooting a 54 flintlock , i wouldnt want to take a shot at a real bear even with my 54 unless i was very , very close and had someone who good back me up .
however the facts still remain that the most common rifles of this time frame would be in 45 cal and smaller with the heavier calibers coming in later with the plains rifles .
this isnt to say that 50 and 54 didnt exsist , the did but simply were not as common but in military applications or smooth bores
but one thing we cannot discount is that clarks rifle was used by him so much that the rifling was being shot out and in need of freshining by the time the corps reached the cascades .