EDITIt's a scatter gun I think. The Widowmaker is the shotgun/rifle combo or fully automatic shotgun I think. The Lawrod is a rifle, I think.
Nifty figure Mr S

From Wikipedia:
Lawrod
The lawrod rifle was the standard rifle carried by all street judges in a holster on the side of their lawmaster bikes. It became obsolete and was replaced with the Widowmaker in 2114.
[SLIDES GLASSES UP NOSE. HALF CLOSES EYES PATRONISINGLY]
I think thats incorrect actually.
Generally it was the scatter gun holstered on the Lawmaster, Im pretty certain.
Widowmaker
The Widowmaker 2000 is a fully automatic shotgun used by street judges. It was introduced in 2114 to replace the obsolete lawrod rifle. It was introduced to the comic strip in the story "Judgement Day".
These photos (from Mongoose or Warlord) poorly illustrate the difference:
Lawrod

Widowmaker

This is the Justice Department weapon sprue.

Info on the Mongoose and Warlord sites regarding these sprues is incomplete, but Im pretty certain that they are as follows, in corresponding order:
Lawgiver MkII
Lawrod
Scatter Gun
Lawgiver MkI
Stub Gun
Widowmaker
I think that the comic may have been inconsistent with what weapon constitutes what. Mongoose have put two and two together and got five before also.
In the Dredd vs Death video game out in the early 2000s, the Lawrod had sniper mode and burst automatic mode. Another weapon, the "Arbitrator" was the shotgun.
Phew. I went full on trainspotter there for a second... breathe Paul, breathe...