Recon Lasgun Fun
 Veteran Build - Warhammer 40k: Darktide 

Another casual build. Boss damage isn't particularly great but you can handle pretty much everything else, even Crushers. Make sure to keep Onslaught active on them as much as possible, because with Onslaught, Infernus burning and Shredder grenades constantly ticking DPS can do respectable damage to Crusher swarms. I know most Recon Lasgun builds prefer having Shock Trooper (and Deadshot too sometimes) but if you don't use your Lasgun excessively you're pretty much literally never going to run any lower than yellow on ammo. Additionally, I don't like how quickly Deadshot wastes your stamina with auto-fire guns, so I generally don't take it anymore. As for melee weapons, you can run basically anything with this build, but I prefer running versatile options like the Combat Knife since you can struggle a fair amount with Crushers and especially bosses if you're not running a high burst DPS melee. 

As for Recon Lasgun marks, it's mostly down to preference, I feel. I run the Mk VIc (green Lasgun) off of preference, but it's not like it's hard to manage ammo for the other two variants. The torrent Mk XII (blue Lasgun)'s DPS is absolutely absurd and it takes one bullet each shot, but you're honestly the closest to "I can actually run out of ammo" using this weapon so it takes some extra management to handle the insane ROF. I can see an argument for the Mk XIV (brown Lasgun) but it's not my preference so I haven't used it with this build (yet).