There are a lot of options for AR15 parts out there. And most of them are cheap, gimmicky junk that will likely cause a malfunction at some point.
If you want a list of some good parts to use to build or modify your existing AR, here you go. These parts are what I personally would look for when assembling.
My personal Go-to AR Parts list
Complete uppers:
-KAC SR-15/16
-LMT MRP
-LWRC IC Enhanced
-Centurion CM4
-BRT Optimum
-Sionics Premium
-Noveske CHF
-ADM MOD2
-Radian Model 1
-BCM BFH
-SOLGW M4-76
Upper and lower Recievers:
-KAC
-Centurion
-VLTOR
-LMT
-LWRC (M6IC lower)
-SOLGW
-Mega
-Hodge
-Expo
-BCM
-Blowndeadline
-Radian
Barrels:
(More combat oriented)
-Centurion
-Hodge
-Daniel Defense
-FN
-Noveske
-BRT
-Criterion
-Sionics
-Capable Citizen
-Geissele
-Rosco
-Expo
-SOLGW
-BCM
--------------------------
Precision oriented barrels, Stainless (shorter life)
-Krieger
-Lija
-Bartlin
-Shilen
-Centurion MK12
-V7
-WOA
-CLE
BCG's:
-FCD
-SOLGW
-Centurion
-Sionics
-BCM
-Geissele
-Modern Armory
-BRT
-LMT
-JP
-FN
-Expo
Triggers
-Any Geissele
-Centurion AST
-Centurion AMT
-SOLGW Liberty Fighting
-SOLGW Liberty Competition
-Sionics E2S-T
-Schmid Tool 2 stage
-FCD 2 stage
-Larue MBT-2S
-ALG ACT
-ALG QMS
Pistol Grip:
-BCM MOD 3
-Magpul K2 and K2+
-B5 P23
Foregrip:
-BCM
-Magpul
-True North
Handguards:
-Centurion
-FCD
-BCM
-KAC
-Ripcord Industries
-Geissele
-Hodge
-SOLGW
-Daniel Defense
-Midwest Industries
-Expo
-FN
-Zev
-Sionics
-CMT
Stocks:
-B5 SOPMOD
-B5 Bravo
-VLTOR IMOD
-VLTOR EMOD
-Magpul UBR
-Magpul MOE SL-S
-Magpul MOE SL
-BCM SOPMOD
Pistol Brace:
-Sba3
-Sba4
Recoil system:
-VLTOR A5 System
-VLTOR A5 tube
-SOLGW A5 tube
-FCD A5 tube
-VLTOR A5 buffer
-Sprinco Green Spring
-Sprinco buffer Springs
Lower and Upper Small Parts:
-Forward Control Design
-Badger Ordinance
-Sionics
-SOLGW blaster guts
-Centurion
-BCM
-Modern Armory
-V Seven
Muzzle Device:
-Surefire Warcomp
-SOLGW NOX
-Forward Control Design
-Cobalt kinetics RCB-KM Keymo
-Epsilon VG6
Gas Blocks:
-Forward Control Design
-Sionics
-Centurion
-BRT
-Badger Ordnance
-Modern Armory
-SOLGW
Gas Tubes:
-Trajectory
-BRT
-Modern Armory
-Sionics
-Centurion
-SOLGW
-BCM
-Lantac
-V7
Charging handles:
-BCM 4x4
-FCD ACF
-Badger Gen 3 ambi
-VLTOR mod 4
Sights:
-KAC
-LWRC Skirmish
-A.R.M.S.
-Troy battle sights
-Midwest Industries battle sights
-YHM
-LMT
-Magpul MBUS
Weapon Light:
-Cloud Defensive REIN or OWL
-Modlite PLHv2 or OKW
-Arisaka 18650 series
-Arisaka 600 series
-Surefire m600 scout series
-Streamlight Protac HL-X
Light mount:
-Arisaka scout
-Cloud Torrent
Light Switch:
-Unity Hotbutton
-Surefire Switch pad
-Modbutton Lite
-Cloud (included with their lights)
Slings:
-Ferro Concepts
-Arbor Arms
-FCD
-Blue Force gear
-Lunar Concepts
-Haley
Optic:
-Nightforce ATACR 1-8
-Kahles K18i K16i
-Nightforce NX8
-Trijicon Credo (1-8, 1-6, 1-4)
-Steiner T5xi
-Steiner P4xi
-Vortex Razor (1-10, 1-6)
-SAI6
-Primary Arms Compact PLx 1-8
-EOTech EXPS 2
-EOTech EXPS 3
-Aimpoint PRO
-Aimpoint Comp m5
-Aimpoint Duty RDS
-Aimpoint T2
-Vortex AMG UH-1
Optic mount:
-Badger C.O.M.M. mount
-ADM AD Recon mount
-Trijicon Q-Loc mount
-Unity
-Scalarworks
-Midwest Industries
Tools:
-Midwest Industries URR For the upper, for barrel nut or muzzle device work.
-Lock and Hold magazine well block for lower work.
-Geissele reaction block for lower work and castle nut work.
-Magpul Bev block is great for an all in 1 type tool for lower and upper work, barrel nut and muzzle device work.
-Central Forge 5 in. Multi-purpose vise with anvil (Harbor Freight)
-5" Vice jaw pads (amazon)
-Wheeler fat wrench torque driver (amazon)
-FCD Castle nut wrench
-FCD muzzle device wrench
-FCD gas tube pin tool
-Real Avid Pivot pin tool
-MB magcatch tool (brownells)
If you want a list of some good parts to use to build or modify your existing AR, here you go. These parts are what I personally would look for when assembling.
My personal Go-to AR Parts list
Complete uppers:
-KAC SR-15/16
-LMT MRP
-LWRC IC Enhanced
-Centurion CM4
-BRT Optimum
-Sionics Premium
-Noveske CHF
-ADM MOD2
-Radian Model 1
-BCM BFH
-SOLGW M4-76
Upper and lower Recievers:
-KAC
-Centurion
-VLTOR
-LMT
-LWRC (M6IC lower)
-SOLGW
-Mega
-Hodge
-Expo
-BCM
-Blowndeadline
-Radian
Barrels:
(More combat oriented)
-Centurion
-Hodge
-Daniel Defense
-FN
-Noveske
-BRT
-Criterion
-Sionics
-Capable Citizen
-Geissele
-Rosco
-Expo
-SOLGW
-BCM
--------------------------
Precision oriented barrels, Stainless (shorter life)
-Krieger
-Lija
-Bartlin
-Shilen
-Centurion MK12
-V7
-WOA
-CLE
BCG's:
-FCD
-SOLGW
-Centurion
-Sionics
-BCM
-Geissele
-Modern Armory
-BRT
-LMT
-JP
-FN
-Expo
Triggers
-Any Geissele
-Centurion AST
-Centurion AMT
-SOLGW Liberty Fighting
-SOLGW Liberty Competition
-Sionics E2S-T
-Schmid Tool 2 stage
-FCD 2 stage
-Larue MBT-2S
-ALG ACT
-ALG QMS
Pistol Grip:
-BCM MOD 3
-Magpul K2 and K2+
-B5 P23
Foregrip:
-BCM
-Magpul
-True North
Handguards:
-Centurion
-FCD
-BCM
-KAC
-Ripcord Industries
-Geissele
-Hodge
-SOLGW
-Daniel Defense
-Midwest Industries
-Expo
-FN
-Zev
-Sionics
-CMT
Stocks:
-B5 SOPMOD
-B5 Bravo
-VLTOR IMOD
-VLTOR EMOD
-Magpul UBR
-Magpul MOE SL-S
-Magpul MOE SL
-BCM SOPMOD
Pistol Brace:
-Sba3
-Sba4
Recoil system:
-VLTOR A5 System
-VLTOR A5 tube
-SOLGW A5 tube
-FCD A5 tube
-VLTOR A5 buffer
-Sprinco Green Spring
-Sprinco buffer Springs
Lower and Upper Small Parts:
-Forward Control Design
-Badger Ordinance
-Sionics
-SOLGW blaster guts
-Centurion
-BCM
-Modern Armory
-V Seven
Muzzle Device:
-Surefire Warcomp
-SOLGW NOX
-Forward Control Design
-Cobalt kinetics RCB-KM Keymo
-Epsilon VG6
Gas Blocks:
-Forward Control Design
-Sionics
-Centurion
-BRT
-Badger Ordnance
-Modern Armory
-SOLGW
Gas Tubes:
-Trajectory
-BRT
-Modern Armory
-Sionics
-Centurion
-SOLGW
-BCM
-Lantac
-V7
Charging handles:
-BCM 4x4
-FCD ACF
-Badger Gen 3 ambi
-VLTOR mod 4
Sights:
-KAC
-LWRC Skirmish
-A.R.M.S.
-Troy battle sights
-Midwest Industries battle sights
-YHM
-LMT
-Magpul MBUS
Weapon Light:
-Cloud Defensive REIN or OWL
-Modlite PLHv2 or OKW
-Arisaka 18650 series
-Arisaka 600 series
-Surefire m600 scout series
-Streamlight Protac HL-X
Light mount:
-Arisaka scout
-Cloud Torrent
Light Switch:
-Unity Hotbutton
-Surefire Switch pad
-Modbutton Lite
-Cloud (included with their lights)
Slings:
-Ferro Concepts
-Arbor Arms
-FCD
-Blue Force gear
-Lunar Concepts
-Haley
Optic:
-Nightforce ATACR 1-8
-Kahles K18i K16i
-Nightforce NX8
-Trijicon Credo (1-8, 1-6, 1-4)
-Steiner T5xi
-Steiner P4xi
-Vortex Razor (1-10, 1-6)
-SAI6
-Primary Arms Compact PLx 1-8
-EOTech EXPS 2
-EOTech EXPS 3
-Aimpoint PRO
-Aimpoint Comp m5
-Aimpoint Duty RDS
-Aimpoint T2
-Vortex AMG UH-1
Optic mount:
-Badger C.O.M.M. mount
-ADM AD Recon mount
-Trijicon Q-Loc mount
-Unity
-Scalarworks
-Midwest Industries
Tools:
-Midwest Industries URR For the upper, for barrel nut or muzzle device work.
-Lock and Hold magazine well block for lower work.
-Geissele reaction block for lower work and castle nut work.
-Magpul Bev block is great for an all in 1 type tool for lower and upper work, barrel nut and muzzle device work.
-Central Forge 5 in. Multi-purpose vise with anvil (Harbor Freight)
-5" Vice jaw pads (amazon)
-Wheeler fat wrench torque driver (amazon)
-FCD Castle nut wrench
-FCD muzzle device wrench
-FCD gas tube pin tool
-Real Avid Pivot pin tool
-MB magcatch tool (brownells)