I was once told by someone (Blackmoor?) that assistant gunners can fire thier lasguns in Heavy Wpn squads. I understand that in regular squads two make up a crew.
However in HW squads it says 6 guardsmen make up 3 crews. I does NOT say 2 per crew. One can say 1 per crew then three lasgunners. Similar to Special Wpn squads where there are 3 with special wpns and 3 with lasguns, Id say HW sqds have 3 guys with heavy wpns and 3 with lasguns. Think of those marine/chaos units that have 3 heavy wpns, dont the other 3 get to fire thier bolters?.
In addition in the codex, under WEAPONS: It says Lasguns, then it says they are armed with 3 of the following: ...... Blah blah. So I say assistant gunners may fire thier lasguns while the gunners fire the hvy weapons.
Whats your call?