I love the idea of the 5.7, so it was all to natural to end up with a five-seven upper for my AR. When I tried that on my select fire receiver, I instantly fell into sad panda mood… Turns out the bolt carrier group provided is semi auto ONLY. Since its a special BCG, replacements were needed.
Just a pic of the two side by side shows there is not much difference, but enough to kill the giggle switch.