You can buy a schuster plug and leave it full open, and it won't cycle. Dunno about leaving the system fully open with no plug since crud will get in, but I know this IS doable.
Springfield Armory M1A 22" barrel in SAGE EBR Mod 0 stock
Dan Wesson CCO | S&W Model 58 blued | S&W Model 29 blued
Springfield 1954 M1 Garand | S&W M&P 15 VTAC 2