I’m curious as to what exactly is the difference among the different Colt model ARs? Clydes shows about 11 different models. Obviously there’s three of the .22lr models so the remaining of the remaining 8 what is the difference?
6450
6520
6720
6721
6920
6921
6933
6940
barrel lenght, barrel profile and twist ratio, flattop vs fixed carry handle,…
take a look at Colt’s websites 
Specifications are available on the Clyde page for each model. Grab a beverage and read.
I was hoping to get a bit more insight other than just the specs. The whys so to speak.
As near as I can tell
6450 AR-15 9 mm Carbine 16"
6520 AR-15A2 Government Carbine 16"
6720 Semi-auto M4LE Carbine 16" Flat-top
6721 AR-15A3 Tactical Carbine 16" HBAR 1:9
6920 Semi-auto M4LE Carbine 16" Flat-top w/Carry handle
6921 Semi-auto M4LE Carbine 14.5" Flat-top w/Carry handle
6933 Semi-auto M4LE Commando 11.5" Flat-top w/Carry handle
6940 Semi-auto M4LE Carbine 16" Monolithic Rail System Flat-top
