I was googling around looking for pictures of guns like ones Dillinger would have used. I stumbled across a board devoted to the Thompson SMG (that's submachine gun to those who, like me, didn't know!). These are the well-known tommy guns we've all heard of in gangster films. There's a thread discussing the film when it was first announced. They were all excited about it and hoped that it would be accurate in the gun details. They thought Johnny would be good in the part. To quote a member with the moniker 'full auto 45':
"I think Johnny Depp will be a good Dillinger character. Look at his other roles in the past. And he looks young enough to be JD at age 31."A later thread discussed how one of the members of the forum actually has worked on the film supplying authentic-looking gun parts. To quote 'deerslayer':
"Well, finished them and wanted to share a picture. Last five of 10 sets for the upcoming movie. Filming I believe starts in March, though I have no idea when it will be out in the theaters. So, eventually, when you see Johnny holding a tommy gun, you can know that a few of us have put some time and effort into getting them right. Some of the actual guns will be live blank firing thompsons, the others will be dummy guns." Here's the photo he posted of the work he did:

I love how far the film-makers are going to get the details correct. It's little glimpses like these that show how amazingly complex it is to produce a major period film.