Last year worked on a contract down range and we were issued 72 DS carbines (I was also the armorer). Only had one castle nut come loose during the heavy 2 month train up and during the 5 month deployment (fired lots of rounds down range). Guns came with a 16" 1:9 bbl but I swapped mine out for a 14.5" 1:7 because some of the UK training ammo messed my bbl up (ammo's fault)
With 14.5" and M7 bayonet
Working pic
CD