Gloob, you're one of the people that diss the Loadmaster on Midway, aren't you? If you had a clue, you'd realize smacking the side of a bored hole will reduce the volume, not increase it.
No, I've never done that. I have several clues, but I'm coming to a different conclusion as you.
Kingmt has posted what I'm thinking. If you smack it with the pin in there, you will make it oval... but the min dimension of the oval will still be near the same diameter as before, forming around the pin. Thus, when you ovalize/egg-shape the hole, the internal volume of the hole is increasing. Kinda like trying to take an unsized case and getting neck tension by crimping with the bullet seated; it doesn't work that way. You can't make the internal volume of the hole less than that of the mandrel that's in there, unless the mandrel is more elastic. And if you're applying pressure on just two faces around an inelastic mandrel, the hole will simply enlarge in the other dimensions when the metal flows. Or in this case where the pin and rod might be of similar material, you might ovalize both the hole and the pin, together, to where the deformed pin can't come back out of the hole due to the gross shape of pin and hole and/or locked-in surface imperfections, but you might not be making a true pressure/friction fit.
If you were to smack the rod without the pin in it, then tap the pin in, or do it my described way, you would not be buggering the hole as much. Methinks, anyway. Your thinking may be different, depending on which clues you're choosing to focus on.
In practice, putting the pin in and smacking it might work the best. But I would have tried it another way, first.