A Plus Airsoft 6.08mm Nickel Coated Copper Rectifier Inner B
The A Plus Airsoft 6.08mm Nickel Coated Copper Rectifier Inner Barrel is closer to tight bore rather than wide bore, so you're expecting more power rather than range. It may add 20 - 30 fps when switching it with a standard inner barrel but it will also potentially make your AEG more accurate.
They come in 4 different lengths. 320, 370, and 410 and 510mm.