Agreed. Sidearms is the better answer. It's another example though of an ambiguous clue in the DR and I expect there will be complaints over this or they might accept both
A handgun is a sidearm but it's also a firearm isn't it? I'm sure they are looking for sidearm but I think the DR has left itself open to complaints again
http://www.thesaurus.net/handgun
This lists about 40 synonyms - including firearm but not sidearm.
I agree that unless the setter was careless the answer is sidearm,but I'm just saying I expect them to get complaints again