I don’t think you will find a jewelers saw to be very satisfactory
for working inside a trigger guard.
The blade clamps will get in the way. Also the useful cutting length
of a blade is only about 2-1/2" you would be able to use much less.
the first 3 or 4 teeth on each end of the blade aren’t usually any
good so you would have to cut the blade shorter so you could cut
starting right at the blade clamp on the outboard end of the saw.
You want at least 3 teeth in contact with the work.
use the heaviest blades that will allow this. Use the best blades -
for your purpose the Laser Gold blades sold by Rio Grande will cut
steel. if you plan on persisting though a lot of blade breaking –
buy a gross to start with. You will break blades!!