Precision stainless steel 6.01 mm inner barrel PDI for XM177E2, M4A1, SG551, M15A4 Carbine/TC/RIS/SPC and M15A2 Carbine - 375 mm. Extremely accurate and hard barrel from polished stainless steel SUS304. The barrel without any additional surface made, which is in precise barrel undesirable because it can result in uneven coverage of the surface which in result can reduction accuracy. The barrel is made of cold forging technology, which is also used for manufacturing for the barrel of guns. This is the precision production with Japanese manufacturing tolerance of +/- 0.002 mm. From reason of the precision is especially necessary to use only high-quality airsoft BBs
and barrel regularly cleaned, otherwise there may be "asphyxiation" of weapon.