Pounding on an aluminum rod with a hammer is more likely to damage the barrel.
I watched a guy drive a squib out of his 9mm using a steel section of a pistol cleaning rod. He didn't have it centered on nose of the bullet and it put a small nice gouge in the barrel. The range owner uses the aluminum because of that type of problem. When you drive the female end into the bullet the end flares out over the top of the bullet and pretty much centers itself over the nose and if you do miss aluminum is a lot softer than steel, less likely to damage the barrel.
Since last September we've had a huge increase in reloaders at the range and I've seen a lot of squibs. In fact we "listen" and watch for them all the time now. I also bought a set of Peltors, (expensive but worth it) and you can hear the "pop" most of the time. When we do we cease fire and head right to the shooter.