If anyone else is considering the regen's in Titanfall here are the requirements for each that you have to complete as well as hitting 50 again.
2ND Generation Requirements
Reach Level 50

3RD Generation Requirements
Complete the following Challenges:

EVA-8 Shotgun: If It Moves…
EVA-8 Shotgun: Top Gun
40mm Cannon: If It Moves…
40mm Cannon: Titan Killer

4TH Generation Requirements
Complete the following Challenges:

R-97 Compact SMG: If It Moves…
R-97 Compact SMG: Top Gun
Plasma Railgun: If It Moves…
Plasma Railgun: Titan Killer
Satchel Charge: Top Gun

5TH Generation Requirements
Complete the following Challenges:

Longbow-DMR Sniper: If It Moves…
Longbow-DMR Sniper: Top Gun
Quad Rocket: If It Moves…
Quad Rocket: Titan Killer
Charge Rifle: Critically Conditioned
RE-45 Autopistol: If It Moves…

6TH Generation Requirements
Complete the following Challenges:

R-101C Carbine: If It Moves…
R-101C Carbine: Top Gun
Arc Cannon: If It Moves…
Arc Cannon: Titan Killer
Sidewinder: Titan Killer
Gooser Challenge

7TH Generation Requirements
Complete the following Challenges:

Spitfire LMG: If It Moves…
Spitfire LMG: Top Gun
Triple Threat: If It Moves…
Triple Threat: Titan Killer
Mag Launcher: Titan Killer
Brain Surgeon

8TH Generation Requirements
Complete the following Challenges:

G2A4 Rifle: If It Moves…
G2A4 Rifle: Top Gun
X0-16 Chaingun: If It Moves…
X0-16 Chaingun: Titan Killer
Charge Rifle: Titan Killer
Fresh Squeezed Challenge

9TH Generation Requirements
Complete the following Challenges:

C.A.R SMG: If It Moves…
C.A.R SMG: Top Gun
Executioner
Archer Heavy Rocket: Titan Killer
All I Do is Win
Look Out Below!
40mm Cannon: Critically Conditioned

10TH Generation Requirements
Complete the following Challenges:

Smart Pistol MK5: Top Gun
Hemlok BF-R: Top Gun
Kraber-AP Sniper: Top Gun
Disarmed
MVP
Deadly Apparition
Death Reincarnate
X0-16 Chaingun: Critically Conditioned
Plasma Railgun: Critically Conditioned