A ctg. version of a Howdah pistol really needs a back-action lock, like the one NitroX has posted above.
Pedersoli did a credible job on their flint and cap lock versions, but their ctg. guns are sickening.(almost make me barf)
The flintlock actually looks fairly good and in .58 or 20 bore, would be fun.
As to loading "up" the .410 brass shell, I suspect the limit might be in the 20,000, maybe 30,000 PSI range at the most.
The Casull range of pressures, ie: 57,000PSI are WAY too high. That's the same breech pressure as a 9.3x62.
In .45 Colt, if loaded the same as for a Ruger, Freedom Arms, or TC Contender, in the 29,000psi range, that would put a 300gr. bullet out at about 1,300fps.
So, yes, that would handle a tiger - if it was hit correctly.
Same with grizzly.
The question is, what is the pressure limit for that gun?