The Noveske KX3 and the original Noveske KFH were designed to be used on SBRs. According to John Noveske, there are no functioning issues running them on 16" barrels, but the longer barrel wasn’t the intended purpose for the design. I have examples of both and they do indeed perform as intended on SBRs. I tried one briefly on one of my 16" barrels, because someone else had asked me this same question. I had heard of alleged functioning problems on 16" bbls, but no one was able to provide first hand reports that could be verified. This prompted my call to John and my subsequent, albeit brief, test.