Tanio Koba M4 AEG airsoft Twist Tightbore Barrel. Twist in barrel creates a more accurate BB shot down the field, increasing both accuracy and range. For use with hop-up (previously corrected) guns. Ideal to use with AEGs that shoot under 350 FPS or around 1 joule. Great for stock Marui aegs as well. Not recommended for guns shooting over 350 FPS.