I need to staple or nail some 1/8" hardboard to the back of a bedroom mirror
frame to help hold the mirror in place. The staple thus needs to go through
the hardboard and into the old wood (probably maple?). Since it's time I
own a staple gun, I was thinking of getting this one for the job:

Stanley TR250 SharpShooter Plus Heavy Duty Staple/Brad Nail Gun
http://www.amazon.com/Stanley-TR250-...2249029&sr=8-2

(unless someone recommends another one to me).

Is this sort of staple gun up to this kind of job (with what size staples)?
My intuition tells me to try 5/16" staples, but I would be happy to listen
to the voice of experience.

My intuition also tells me that hammering on a frame holding a mirror is a
task that that should make my caution flag go up. Actually, would be more
afraid of the prospect of trying to replace a uniquely-shaped mirror than I
would cleaning up the broken glass! I hate to think about the idea of
using duct tape for this repair because then I wouldn't be able to look at
myself in the mirror... : )

Thank you,
Bill