We did something like that once
We were using a Church in the middle of renovations to film a scene that involved an armed team rushing in, and we had proper replica weapons, shotguns, MP5s, even an M4a1 rifle and a couple of pistols thrown into the mix.
First thing he did was tell the police we were filming with weapons, even though we were indoors there was a chance that someone outside might grab a peak of some guys wearing all-black and carrying automatic weapons. Indeed, one of the extras thought it'd be nice to grab some fresh air and forgot he had a rather large rifle slung over his shoulder. Luckilly we pulled him back in before anyone saw him :D

If my mate ever finishes editing it I'll post it on /links
(Canazza is mostly listening to Yes, Fri 6 May 2011, 11:02, Reply)