Ok, had to go through 17 pages to see what people speculated about the weapon from the safe was. I immediately thought of a couple of ideas to toss out there, since I was more fixated on this mysterious weapon than Riley's sexuality, Pippen's mole/not-a-mole status, or that list thing that Brick and Tardust had with them when they captured Lizzie in the previous chapter.

Since I believe the safe is from Burt's store, and (paraphrasing here) approximately 10% of his inventory was legal, I'm going with the following for the weapon (in order of most to lesser likely)

M72 66mm Light Anti-Tank Weapon (LAW)
AT-4 84mm Rocket
M203 or M79 40mm grenade launcher
M47 Dragon wire guided rocket
RKG-3 (Anti-Tank Grenade)
RPG-7 (Rocket Propelled Grenade)

I go with the LAW because Burt is a Vietnam Vet and would probably hold on to something like this if he saw one (doesn't mean he got it in Vietnam, just that if he saw one, he'd do whatever to get it). Same would definitely be true for an M79 since it looks like a big-mouth shotgun, but shoots only 40mm grenades. However, I put the AT-4 before that because of its firepower. I like the idea of Burt holding onto a Dragon is way cool with me (this being a fiction and all), but I don't remember too many military urban legends about that rocket system getting out and in the possession of "Cold War survivialists."
I place the Soviet items at the bottom because, while totally believable that someone like him could get one or be in possession of one, I like to think that Burt doesn't want too much in his store that "Charlie" used to use towards him.

Anyway, I am thinking that Scratch is holding the weapon back to case Tardust cannot set off the other tankers. We did hear more than one explosion from the Tower's perspective, but when we focused on Lizzie with Tardust and Bricks, only one exploded.

So, who's up for a hockey game now?