T-N.T. Precision Double I/D Air-cushion Inner barrel
only at the outlet of a large inner diameter. 
Therefore, gas envelope effect, part of the gas "coated" the BB, front guide airflow sharp and straight.
Rear of BB's airflow is more strong...
some people think that『T-N.T. Air-cushion Directional Inner barrel』is "whole branch is large inner diameter"...
the right answer is - only front end ratio is the large diameter, 
not entire, the rear end of the inner diameter of the inner barrel to maintain 6.03mm.

More straight, more accurate, and more effctive range!!
No more jamming, BB broken, but working smooth!!

Just simple install steps, then you can see the significant results!!
In the case does not raise the kinetic energy, but effective range can improve about 30% ~ 50%!!

Material : bronze with electroplated chemical nickel surface.
Inside diameter : 6.03~6.35mm (different inner diameter in barrel)
Outside diameter : 8.5mm

Item Code: TNT-HOP-SP01-106