Originally Posted by
militarymoron
yes, that's wrong. it's not in 'full return'. the BCG is at the beginning of its forward travel when it gets stopped by the bolt catch on an empty mag, so there's very little inertia. it's mostly energy stored in the spring pushing it against the bolt catch.
when the BCG contacts the bolt catch, it's steel against steel. the receiver doesn't get impacted - the bolt catch just presses against it in the slot.
with a falling hammer and separated lower, it's got a lot of inertia as it's at the end of its travel, as it slams/impacts the thin aluminum wall. so, it's steel vs. alum, and an impact.
take a steel hammer and press it against piece of aluminum without impact. just press the hammer against it with all your strength. you might scratch the aluminum a bit. now take the same hammer and hammer the piece of aluminum as you would hammer something normally, impacting it. that's the difference between the two.
in other words, don't do it if you don't want to intentionally damage your receiver.