This one belongs to a neighbor friend, so I'm going on what he's told me he's already dealt with. It IS marked Israeli, and it is most definitely a 40S&W. Magnum Research mags are too wide for the mag well. I'll get a better hands-on in the morning and pull some partial #'s and proof marks to see where that leads us.
44 AMP---I DO believe you're on to something. I'm definitely not in the loop on DE in many ways, so that helps a bunch. If I had to guess, I'd say you pegged it.