Red river, Not to run you down as others have already, but to clarify to those who have skimmed this post, your post claims that your guide had an "old single-shot .45-70" which surely would not have been loaded with anything like the new hot loads that newer rifles are capable of firing without damage.
A buddy of mine pays a man nearby to reload for him in all kinds of high velocities, i.e. 8mm mauser 180gr SP at 3000+ fps, 139gr AP SKS up to 3200 fps, and 280 gr TB .45-70 out to 2300 fps. Claims it's kinda a rush to shoot, firstly because it kicks the **** out of him, and secondly because he's not absolutely sure that the gun will fire everytime, rather than blowing up. He takes mulies with it, took one last season at 250 yrds, through both shoulders like a frieght train. I'm sure that a well bonded bullet at anywhere near this velocity (hopefully slower for safety's sake) and within 50 yrds would penetrate the hide of a capie pretty well.

GOTTA LOVE THAT MARLIN MAGIC!!!!