The purpose of this build is simple - kill every NPC with highest damage possible as quickly as possible. Classified sentry is core of most team compositions in Resistance and it makes missions like Stolen Signal or Legendary Napalm much easier (the latter one becomes a breeze). With the build you mainly have to focus on these statistics:
-enemy armor damage (EAD)
-damage to elites (DTE)
-critical hit chance (CHC)
-headshot damage (HSD)
Of course if you look at every piece you will notice slight variations (Health as major stat on kneepads - the EAD is so low I think it's better to have Health to survive close quarters). Half the talents can be swapped for something else like Strike Back or Tactical Advance but I think getting flat 12.5 % crit chance from headshotting someone and pulsing them or being able to heal your allies with 30% of their max health when you pop a medkit is far more valuable than slight buff to your atrociously low Skill Haste or dancing between cover when you should constantly mark enemies and deliver heavy damage.
Also skills are of personal taste. Since Pulse Tactical Scanner adds flat 5% damage and you can slot in CHC Pulse mods it gets much better than let's say First Aid Booster Shot. The Support Station with Lifesaver mod is here because if you get dropped you can crawl on top of it to block most of NPC damage and get automatically revived. Also you can blow it up for 33% of your maximum health which is more than Overdose First Aid - and the support station can be blown up when aiming down the sights unlike First Aid as of patch 1.8.
Your primary weapon is Urban MDR - an Assault Rifle with baked in EAD. Take talents that increase EAD or DTE more and avoid Brutal - you get Headshot Damage in huge quantities plus you gain 100% of it when you mark someone with 6 stacks so you will get more gains with something else providing your targets are that much tanky. MDR is excellent because it is very stable, the gearset gives it huge accuracy bonus and it can fire in quick succession.
M700 Carbon is for long engagements or when you need to nuke something with 4 million Headshot crits. Carbon version allows for more mods - if you think you are better with M700 Tactical then you can grab it. Avoid M44, it has more damage on paper but is less stable and as a result you will have to adjust your aim and fire more slowly to hit your targets. Devil is also a good alternative for M700 because of it's exotic talent but having MDR already it is rather useless - I personally always swapped it away since the bloom on reticule was huge after a shot plus again M700 is better for long engagements.
For stat distribution go as far as you can with Firearms and get as much Stamina as you need to unlock Destructive. The reload speed on holster is to increase your damage and avoid moments when Rioter with baseball bat is rushing you and you are chicken dancing while waiting for reload to be over. If you think you need that 4.0 CHC or 4.0 EAD then go for it. This is loose suggestion. Avoid Skill Haste - you are not a dedicated healer and you will have to sacrifice your damage in order to get SLIGHT boost in your skill usage - if you need more then just pop some water for 30% Cooldown Reduction. That's the only consumable you should use since Explosive or Fire Ammo have been heavily nerfed and don't do as much versus AI mobs as they used to.
Final note - This build is OK for Clear Sky but you are better off with Striker, Reclaimer or D3-FNC than Sentry. Clear Sky is all about objectives not kills, so don't use it. I do and it is mediocre/requires positioning when that incursion is all about speed.