On returning from a range trip some time ago, I was considering the slamfire shotgun. I have one and my buddy has one.

Musing to myself on the long drive back, my mind wandered to the pump-action AR, and this is where my thoughts went.

Suppose you took a pump-action AR upper, and mounted it on an M16 lower. Of course, you would use the full-auto carrier in the upper.

So you pull the trigger with the selector set to auto, AND HOLD IT BACK, and just start pumping the action.

It seems to me that you could slam fire the whole magazine. But the real question is, would it be safe? I would think it would be in battery with each shot, same as if it was gas powering the action. Am I correct?

Like I said, it's a goofy question. There would be no real reason to do this, other than just for laughs.

But as a technical question, I think it makes for an interesting discussion.

Have at me then.

I have shot a full auto shotgun.....even though I am a gun guy, it was not fun....

I bet it wasn't.

But to be clear, I'm talking about using a 5.56 pump-action upper on an M16 lower.

I don't see why it wouldn't work. Everything would still get tripped and make its full rearward and forward travel as long as I'm picturing it correctly in my head. I'm not sure if the slow ass rate of fire would cause any timing issues or not tho.

Hmm could a company legally sell one if they permanently attached the upper to the lower from the pivot pin?

That would be my concern also. I think the mechanics would be pretty much the same, but would the reduced speed of the cycling of the action have an effect?

Maybe I shouldn't let my mind wander. Sometimes it takes a while to find its way home, and you end up with what we have here.

Two reasons that it would be safe and would work.
1. It's almost impossible for an AR15 to fire out of battery. Unless the firing pin is too long, or the bolt tail is too short, it can't. The firing pin doesn't protrude from the bolt face until the bolt group is locked.

2. Full auto, or slam fire in this case, is controlled not by the sear on the trigger. It's controlled by the auto sear. The auto sear holds the hammer by the hook on the back and is tripped by the bottom of the bolt. That's why the standard bolt has more metal. It trips the auto sear and the hammer is released when the bolt is in battery.

on a m16 lower it would be fine, It would not be "slam fire" as the sear would trip at the correct timing.