The BARREL MOUNTED BIPOD UPPERS
$1,300 - Barrel Mounted Bi-pod Uppers
24" chrome lined, parkerized, threaded bull barrel (.936" gas block) chambered in 5.56 NATO 1 in 9 Twist.
Inconel Gas Tube (super high temperature resistant, The same material used in rocket nozzles vs. simple stainless steel)
M-Lok free float handguard - handguard length varies with bipod type.
Bipod types available are M60, AUG and RPK
The 24 Inch barrel has debatably more muzzle velocity depending on ammunition than the 20" but a big thing you're gaining with the 24" is more leverage over the muzzle for enhanced control. Since the bipod is mounted on the very end of the barrel you will have a larger moment arm, which should shrink your cone of fire and give you more control for shifting/sweeping your fires.
A shorter barrel is going to be handier, lighter and work with blanks more reliably with standard BFAs
Bipod Selection:
AUG bipod with hardware is 1.072 LBS light, height adjustable, low profile. Manipulation is similar to M60 Bipod. In exchange for its lightweight, its all-aluminum construction is the least robust. It also requires a 24" barrel because the bipod needs an exposed barrel section to be folded up along its length.
RPK bipod with hardware is 1.116 LBS This bipod is simple, sturdy and pretty light, and fast to manipulate. It absolutely requires a slim handguard and requires a barrel length of at least 19" so you will have room to rest on the handguard with the bipod folded up.
M60 bipod with hardware is 2.158 LBS heavy, height adjustable, robust. This one gives you the widest options for hand guards and barrel lengths.
Videos for uppers:
Automatic Rifle Theory and concepts: (upper related videos)
at checkout