Artemesia said:
Bolts are just very painful bullets. That use a propellant to accelerate rather than the standard "minituarized explosion launches the small metal thing at the big fleshy thing" routine guns tend to do. That also explode.
Bolts are large but that doesn't make it any easier to hit a target. You still need to aim. The difference in the standard assault rifle round(The M4A1 fires 5.56x45mm rounds if memory serves) and a bolt is probably not all that large when it comes to the front, "penetrating" end. At least by my understanding, a bolt is the size of a 10 gauge shotgun shell. Really, when put up against a human body(or daemon body, or tank, or ork, or daemon engine, or...) and compared, the difference in size would not be great enough to be able to say that a bolt makes it much easier to hit a target.
Now, if bolts were the size of cannon balls...
Not that I have anything really to add to the discussion further at this point, now that it has taken a new direction, I could have sworn that a bolt round was roughly the size of a coke can (perhaps that was a heavy bolter round?)
A bolt shell is 0.75 caliber, and a heavy bolter shell is 1.00 caliber, if memory serves me correctly.