This subject has been vaguely covered in other forums, but not this question specifically. Some manufacturers (BCI Defense and Standard Manufacturing, to name a couple) internally mill their lower receivers to M16 specifications (less the auto sear pin hole!) but, for some reason, also mill off the selector stops, or "nubs," which prevent over-rotation of full-auto selector switches. If lowers such as these were to (legally!) be converted to full-auto, would rotating the the selector switch 360 degrees cause any damage internally? In the absence of selector stops, would moving the selector from "safe" to "auto" or vice-versa cause problems, or would  the group remain fully functional? I know that many modern auto selectors have built-in detent stops, but I'm referring to mil-spec selectors that have the 360-degree detent channel.

FA selectors have internal stops that will prevent overrotation in almost all cases.

ETA: if a 3pos selector had a 360 degree channel, it would most likely act as a non-detent safety position.

Many modern auto selectors do have the detent stops built in by making the detent channel connect only the three detent holes without circling the piece entirely. Here I'm referring to the mil-spec auto selectors made by Colt, FNH, etc. which have detent channels that run a full circle.

Won't cause damages.  The factory Colt FA selectors I've seen all have the detent groove 360 degrees, even where there are no detent holes.  Without the selector stops, the selector is able to rotate the selector all the way around.

When we (while I was still at BAD) made revisions to the BAD-CASS-3P (3 position), as it was called at the time, we got rid of the 360 degree channel groove.  During its development in early 2010, we were wondering why the detent groove went all the way around, past the detent holes, but we made our FA selector according to milspec anyway, and only deleted the mystery groove in later revisions when we've determined it didn't do anything useful.

On a semi auto selector, the detent groove only exists between the SAFE and FIRE detents, but that's not the only thing that's different.  Semi auto detent holes are also shaped differently to stop over rotation into a position where the detent groove doesn't continue.  With enough force, i.e. with a mallet hitting the lever, a semi auto selector can overcome the detent hole and continue to rotate, I've never seen anyone do it without a tool though.

A semi auto selector can't use the M16 selector detent hole geometry.  With or without a detent groove, the shape of a select fire selector detent groove will allow the detent to over rotate without much effort.  Ask me how I know

On a semi auto receiver, selector stops are unnecessary.  The shape of the detent hole is more than adequate to prevent over rotation.

Your opinion. While I'm not currently a Type 07/Class II S.O.T., I have ambitions of possibly moving in this direction in the future, when time and finances allow. I have every right to ask questions as to the function and compatibility of various types of firearms, so as to learn their ins and outs. As can be seen, the function of automatic weapons is minimally covered on the forums, hence why my only two posts involve the topic. All of my hundreds of other questions have been answered without needing to create a single thread. If I had ill intent and were senseless enough to publish my wayward ambitions on forums, I would surely deserve the time in federal prison which would follow. By all means, indicate your suspicions. But if you have valuable information to add, feel free to do so.

I've read that Colt included the unnecessary 360-degree detent groove because it was cheaper to manufacture that way, and didn't present any functional problems when used with selector stops.

I’m a retired cop/Det SWAT team leader and I find this thread informative without suspicion of ill intent by the OP.

Ask away OP. I'll tell you what I know.

Becoming an 07/02 SOT doesn't cause you to know anything about full autos. It's just the result of some paperwork and money.

I agree, at the time of development, it probably was easier to machine the full circle.

Unless they CNC mill their selectors (they're MIM or cast), I don't think it'd cost more or less to have the groove where there isn't a detent hole, but that's just logic talking.  With the selector stops, the selector can't over rotate.

On many Colt semi auto receivers, the stops were removed.  They don't do a very thorough job and leave the remnant of the stops in place.  I can't explain why they'd bother.

Thanks Duffy! Always good to speak with people who have big-name manufacturing experience. So over-rotation of select-fire selector switches wouldn’t misalign or cause any malfunctions of the internals? One could go straight from safe to auto or vice-versa, or continuously spin the selector around 360 degrees with no issues? What function would occur while the selector was over-rotated between safe and auto? Would it act as a “safe” position?

A properly made semi auto selector can't over rotate, with or without the selector stops.  I've seen them rotate before when sufficient force is applied.  It just keeps spinning on top of the trigger tang (the horizontal housing that holds the disconnector), I don't believe it'll cost any harm.

For a select fire selector and trigger group, when the selector over rotates and points to 6 o'clock, the weapon doesn't fire, same as if it were on SAFE.