On my 16" DI midlength adjustable gasblock AR and Saker ASR 556K, I had a significant amount of blowback with rapid rates of fire, however the same can on my MCX 11.5, I have very little blowback, and almost none at a low rate of fire. Some cans produce much higher amounts of gasses than others, such as my Ultra 7 on my PWS Mk109 with 300 BO S&B 200gr subs has quite a bit of blowback.