Let’s see what happens when he engages an angry charging moose with a Model 57. I bet that will be the last you hear from him.
People with .454s have killed large bears with 1 to 2 shots to the vitals. Yes they charge fast sometimes but the small caliber gun is useless. Here are some stories from people from the wild who totally disprove your theory. Tell your friend in Maine to upgun before he gets himself killed: http://www.thefirearmblog.com/blog/2009/08/31/man-kills-charging-bear-with-454-casull/
I already had this talk with him. He's no dummy. He has longarms but can only guarantee that at any moment, he'll have access to a sidearm. Understanding there is no perfect gun, he first considered the range of threats and their probability. In his case, the likely scenarios range from an angry moose, varmit control and a trespasser with ill intent. I suspect he considers the odds more or less even with a little more concern given to the two legged trespasser of ill-intent than an ill tempered moose.
Should he find himself between a cow moose and her calf, a large caliber hand gun gives him a better chance of survival against such a large charging animal only if he can control it well enough to get at least one “good” hit. However, If a moose or black bear confronted at close range is rabid, one shot through the heart with a .300 win mag may not be enough to deter it's attack. So, the large bore handgun for close quarters self defense against a large charging animal is no guarantee of a successful outcome.
A moose being only one potential threat, he also has to be concerned with two legged threats in the form of assorted trespassers presumably armed and having unknown intentions. For these two legged threats, a large bore revolver is suboptimal for self-defense.
For varmit control, the large bore handgun is also overkill. The coyote moving at 50 yards is going to be a challenge with any handgun having open sights but for most shooters, the easier to control gun will result in a higher probability of a hit. Should a rabid fox charge him, the large bore handgun is again impractical. It may be a matter in this case of spray and pray.
Simultaneously, if he runs into trouble with two legged animals, the firepower of a semi-auto with a spare magazine gives him a range of options unavailable with a big bore six shooter. The 5n7 with spare magazine gives him 40 rounds in a lightweight easily controled gun. It gives him a chance of detering the charge of a large animal, enables him to deal with varmits within 100 yards and let's trespassers know he means business. Should trouble occur with a trespasser, the 5n7's firepower enables him to stand his ground, hold out, or make E&A.
There is no perfect choice, a measure of luck is needed to fill in the gaps for each scenario.
Go read the link carefully and stop trying to justify this insanity. There are few stories on there how small caliber handguns do not do the job even the .44 Magnum doesn’t get it done all the time. Killing varmints and human intruders is a job the 57 does well. I like the 57 it is an excellent weapon and I intend to get one. However it is not meant to deal with bears, moose or any large dangerous animals period. The bullet mass of the 57x28 round (even the military version) is too light and its penetration effects does not have the power to make the massive wounds required to severely wound or kill a large animal like the big hardcast slugs can. Even the lower velocity heavies are superior in this regard as they put one big mass right on target with nearly a ton or more of muzzle energy.
Some gun owners really go overboard and think their weapon of choice can do more than it really can. Many people go to war thinking that their weapons system can do all these things but the reality of combat often proves those theories wrong no matter how well thought out as the unexpected usually happens. The voice of experience always proves true.