PDI barrels are cold-hammer forged from stainless steel, which is the same process how real rifle barrels are produced. They have a superior tolerance and roundness of the inner surface compared to anything else on the market.

This inner barrel is suitable for the Western Arms M4A1 Series. Made of SUS304 stainless steel, inner diameter is 6.01mm and outer diameter is 8mm.

Increase the shooting power of your WA M4A1 significantly well over 400fps!