Two points come to mind, after reading most of this thread. One, tactics come to mind, more than weapons.
I don't think it would have mattered if all the FBI guys had rifles or shotguns, if they hit the suspects car, and get knocked silly by the collision - which was a problem with at least Grogan (lost his glasses and couldn't see well after the collision).
In the frequent hellicopter videos of highway chases, you often see one car, driven by the HP or local police, who rams/pits the fleeing vehicle to disable it. Immediately support vehicles rush in with whatever force is appropriate, and finish the job, knowing that the lead guy has just been in a collision, and needs help. Presumably, this is how these cops are trained to stop chases.
The FBI would have done well to anticipate, "...if a car chase occurs, whoever rams/disables the suspect vehicle will retreat as soon as possible, and the support guys will act (start shooting) until the threat is stopped...". The FBI, of course, doesn't do highway chases, and probably hadn't even thought about these issues since the days of Dillinger, so the brave agents found themselves in a bad place, but they did stop two killers, and taught many others important lessons.
Two, it's darned unlikely I will ever have to stop known armed killers in a car, but the earlier point about staying in the fight makes sense for anyone who has determined to defend themselves. At some point, you have to be prepared to fight! There was another video circulating a couple of years ago, of a lone deputy who pulled over a speeder, who started pulling a gun out of a toolbox. After a lot of shouting and unheeded commands, the deputy finally starts shooting, but only wounds the gunman, who kills the lawman and drives off. The victim was probably a nice guy, who wasn't ready to fight effectively when he desperately needed to do so.
