Watch this video from AirsoftJunkiez on M4 Hopup Stabilisation, Accuracy, and Midcap Feeding Correction... "This setup will increase Accuracy as well as help midcaps to feed more efficiently in your M4 platfrom based gun. This eliminates play within your barrel and outer barrel as well as left to right movement with the hopup chamber. Hopup setup parts listed below.

• PROWIN Hopup
• Maple Leaf 70 Degree 60 degree maybe used as well. Includes flat nub.
• Oring size. 5/16 OD and 3/16 ID
• Teflon Tape."