Here's my opinion:
Even in Halo 3, when the BR was a 4 shot, is really wasn't an incredibly common occurance. For a steady 4 shot conversion, you either had to be very good or have the drop on your opponent. There wasn't always a 100% chance you'd land all 3 bullets, resulting in a lot of 5 shots in gun battles.
Now in Halo 4, you have a BR that is again not guaranteed to land all 3 bullets per shot, but also takes an extra shot to down an enemy in a straight gun battle in a longer kill time than that of the also 5 shot DMR.
Therefore, once you put the DMR 1 bullet landing = BR 3 bullets landing, since the majority of the time not all 3 bullets will land each time, obviously the BR will always come up short
So, I say go ahead and make the BR a 4 shot again, leave the fire rate as is, and just see what happens. If it does end up giving it a huge advantage over the other weapons, then explore other options
