i am not a firearms expert, but I have always been told that a knowledgeable person can buy or make the parts required to turn a semi-auto rifle into a full auto, or something close enough to full auto as to not make a difference (i.e. the bump firing). The solution is not to make doing so illegal. The solution is to make it much, much harder/impossible to get hold of the underlying weapon.
A knowledgeable person can also make a bomb out of readily available household chemicals. I don't know how easy it really is to change a semi-auto rifle to fully-auto - but if we can make it harder to do so (by changing the way they are made or making the parts needed illegal or making the act itself illegal, etc.) then we should do so. I am in favor of allowing people to own guns but think it should be as impossible as we can make it to obtain or make a fully-automatic weapon.