The obvious...
Doing this increases the projectile weight by the weight of the stick. This causes increased resistance to movement and therefore increased pressure inside the burn chamber of the case. (Don't look for that term anywhere, I just made it up; hopefully most everyone understands what I mean.)
Depending on what caliber we're talking about in the first place, this means the payload could be tripled, perhaps more. I've forgotten the formulae involved, but that substantially jacks up pressure.
This may not blow up the gun, but it's not going to help, either. Probably end up with a 'proof test' load, anyway. Probably a cratered or blown primer and the case beat bad.
Because your stick is a fixed weight, it will affect guns with smaller weight projectiles more. A 9x19 will be severly overloaded, a .50 BMG will have some increase, but perhaps not a dangerous level, and a 155 mm howitzer wouldn't notice at all.
I think Werewolf was being facetious when he suggested you try it and report. I would recomend against such an experiment. But if you must, tie the gun to a tire or something, fire it with a long string, wear safety glasses and take along a movie camera of some type to record the experiement for later review. You may want to take along a large box to collect and transport what's left of the gun, too.