This is not remotely true, even at 4ft average, that's 227 thousand miles. Mars, at its closest, is 34 million miles. In short, all the guns laid out wouldn't even get us 1% of the way to Mars...... but hey, making shit up is fun too right?
IF THERE ARE 300 MILLION GUNS IN AMERICA, IF WE AVERAGED HANDGUN AND LONGARM LENGTH AND LAID THEM END TO END; WE WOULD REACH MARS, AND BACK AGAIN, AND BE ABLE TO RETURN ONCE MORE.