I just thought of something regarding the flash-forward. Walt created two batches of ricin in the course of the show - one to kill Tuco, and the other to kill Gus. Both times, the reason he wanted to use ricin was so that the murder would be undetectable. However, on his 52nd birthday, he has just got himself a .60 caliber machine gun. He is planning to do some very open and obvious murdering. Why would he need the ricin now? Who does he need to kill covertly, as opposed to the overt killings he is planning to do with the gun? Why would it matter at this point?
Walt has gone out of his way to save Hank and Jesse. Yes, it was mostly because he also wanted to save himself as well, but I also believe he does care for them. Walt still tries to maintain the illusion that he is doing all of this for his family, this includes Hank and Marie and Jesse. I think that he will still try to maintain his family. The show has always been about Walt fixing one problem, only to have another one pop up. As we saw with the train heist, it was perfect until the kid was shot. Now, Hank knows the truth an Walt has threatened Hank, but I'm guessing that Walt will not purposely hurt Hank. I also see consequences from Jesse throwing the money around. Something like that will show up in the news the next day. Jessie's fingerprints are on the money, so that could be an issue. Keeping all of that in mind, I believe the gun is not being used on Hank or Jesse, neither is the ricin. I think the gun is part of a bigger plan of Walt's that involves trying to fix a problem. It may be used in a trade for something else or it could be used as a way to set someone up or it could be used as a way to blast through a door or something. The ricin could be Walt's own way out or it may be the only way to get to someone without a big shootout Scarface style. I think we're going to see Walt make Hank a hero, but without Walt necessarily being the "bad guy". Jesse is the rouge element though that I'm not sure how it will play out. All I know is that every thing in this show that is shown on screen, definitely has a purpose.