Gotcha, I didn't realize just owning a gun for your home was so hard in NYC, I thought a carry permit was impossible.
Fwiu shot guns are easier in NY, maybe talk to an expert if they would help for a mass shooting in a shul or not.
Long guns are typically easier to obtain, but unless open carry is allowed, you can't really carry one. Also, I don't think a shotgun in a crowded shul is a good idea...
I know a shul that has a safe and a few members keep guns there. They pick them up on their way in and put them back on their way out.
Sounds nice and all, but I would never leave my gun in a public location, even if it's in a safe.