Server may be getting pounded. It will work for a minute, then stop working completely. I did see chapter 5 when I clicked on that link.
I just dl'ed the whole book. 10 meg PDF. Here's a link if you want to just right click & then doa "save as" you might have better luck. http://www.atf.gov/firearms/nfa/nfa_handbook/0507nfa_handbook.pdf