I think the present (Lawgiver) is too chunky. It was likely changed as the new one was easier to draw.
For most of the nineties, the Big Fucking Gun was in vogue. The philosopher Simon Bisley once postulated that the reason Dredd never caught on in the US was that he had a puny little gun
At the time the new version was introduced 
, I thought it was being changed to more closely resemble the Stallone gun, but that only really applies to the black casing, red LED, and front elevation.Dark Justice's
introduction of the mkIII only seems to have been cover for Greg Staples incorporating the LED from the 2012 film (and to explain why it jams)
. That seems strange, considering Carlos uses a different design to everyone else.  1122, Gun Crazy, by Wagner & Parente, 1998