Table:
text: AR-15 variants
MT and CR series models
MT and CR series models
Colt_model_no_ Name_ Stock Fire_control Rear_sight Forward_assist Case_deflector Barrel_length Barrel_profile Barrel_twist Hand_guards Bayonet_Lug Muzzle_device
MT6601 Match Target HBAR A2 S-1 A2 Yes Yes 20 in. HBAR 1:7 Ribbed No None
MT6601C Match Target HBAR A2 S-1 A2 Yes Yes 20 in. HBAR 1:7 Ribbed No Factory compensator
MT6700 Match Target Competition HBAR A2 S-1 Flattop Yes Yes 20 in. HBAR 1:9 Ribbed No None
MT6700C Match Target Competition HBAR A2 S-1 Flattop Yes No 20 in. HBAR 1:9 Ribbed No Factory compensator
MT6731 Match Target Competition HBAR II A2 S-1 Flattop Yes Yes 16 in. HBAR 1:9 Short Ribbed No None

text: AR-15 variants
MT and CR series models
MT and CR series models
Colt_model_no_ Name_ Stock Fire_control Rear_sight Forward_assist Case_deflector Barrel_length Barrel_profile Barrel_twist Hand_guards Bayonet_Lug Muzzle_device
CR6724 Colt Accurized Rifle A2 S-1 Flattop Yes Yes 24 in. Stainless HBAR 1:9 FF Tube No None
MT6400 Match Target M4 4th Generation S-1 Flattop Yes Yes 16 in. M4 1:7 M4 No None
MT6400C Match Target M4 4th Generation S-1 Flattop Yes Yes 16 in. M4 1:7 M4 No Factory compensator
MT6530 Match Target Lightweight A2 S-1 A2 Yes Yes 16 in. A1 1:7 Short Ribbed No None
MT6551 Match Target Rifle A2 S-1 A2 Yes Yes 20 in. A2 1:7 Ribbed No None

Question: Name the barrel length for the sight a2 for the factory compensator among the AR-15 variants of the MT and CR series models ?