Well, to be fair to the Mythbusters guys, they were testing a very specific myth, with specific parameters, to wit:
-A *hand (finger)* in the bore, not a metal object, and
-From a *shotgun*
A shotgun is a VERY low pressure gun, relative to the rifles which have Kb'ed and banana peeled as shown on this thread.
Change the myth/parameters, you may get different results:
-High power rifle, flesh & bone obstruction ==> may or may not peel back
-High power rifle, metal obstruction (cleaning rod, bullet) ==> may or may not peel back, but good likelihood that it would. Depends on the exact amount of pressure, the thickness & metallurgy of the barrel, and the extent to which the metal obstruction obstructs the bore - 100% or some smaller %?
I find most of the Mthbusters test to be fair, though they are often inconclusive/non-comprehensive - they run out of time, $$, & interest in a project after a few runs before they test all the possibilities, and move on to the next myth.
Besides, the mythbusters test is irrelevant to Mike's "friend"s' assertion since it is a smoothbore, and he is talking about splitting down the rifling grooves.