Thanks for the info!
Your uppers need to have a "sear relief cut" to work with the M16 auto sear.
Will that affect the reliability of the bolts with my AR-15 lower? I've never had a jam with them, so I'm a bit nervous to tinker with something that works. But then of course, ripping through a 60-round mag of 5.56 with a 7.5 inch upper makes it worth the risk.
Would that also run me afoul of the constant back-and-forth argument about having "M16 parts" (a modified bolt) in an AR-15 when I'm shooting my SBR? Or would that only possibly
(not trying to start a new front in the argument) apply to having actual M16 parts in it?