But with 1.5 orders of magnitude difference in the officially known enumerated types we can be pretty sure the officially unknowns don't wildly vary from knowns. Plus the number of rifles used is so small people who track of this sort of thing would likely have an idea if something weird was happening.

My only caveat is bodies found without a recovered bullet; almost all centerfire rifles have greater energies and sectional densities than normally used handguns, so the bullet is more likely to exit. To get a handle on this we'd need breakdowns on where they happened (e.g. city, almost certainly a handgun, rural, a rifle is more likely, if only because of concealment issues). Or talk to coroners, the wounds will be somewhat different.

You presume too much... these are the conclusions the data support--anything else is just handwaving.