Browning's Invector-DS choke tubes have a double seal which keeps tubes cleaner, and the longer choke tapers are optimized to percentages, not just dimension. The proprietary differential banded gas seal eliminates residue build up and makes chokes easy to remove and install. Integrated spring suspension holds the seal tight while allowing expansion and controlling gas. Incector-DS choke tubes are constructed of nickel chrome moly steel with a chrome silver finish.