> but of course they never had a ton of those to start with.

Really? The vast majority of weapons in the US are semi-auto so I find this difficult to believe.

> the majority of guns Afgan insurgents had were 60 year old bolt-actions

Were they? I would expect they were AK-47 and similar although I've never looked into it.

> so I find this difficult to believe.

Extrapolating from experience in the USofA to other countries in the world is generally not a good move.

The actual numbers, from the time, suggest maybe 10-15% of guns in Australia were "self loading"

( 20% of guns purchased back, not all were semi-automatic, a good many were old unwanted guns that now faced a registration fee if kept )

From a US academic type study that looked at the Australian (and other) gun buyback scheme post Port Arthur.

  Between 1996 and 1997,643,726 prohibited firearms were handed in.

  Prices were set to reflect "fair value" (market value). Individuals with permits could also turn in firearms that they had failed to register.

  Total public expenditures were about $A320 million ($U.S. 230 million33), approximately $A500 ($U.S. 359) per gun. The buyback program was financed by an additional 0.2 percent levy on national health insurance.

  Estimates of the total stock of guns were few and drew on limited survey data.

  Estimates ranged as high as 11 million, but the high figures had no known provenance. Gun Control Australia cited a figure of about 4.25 million, building on the only academic estimate, then roughly twenty years old.

  The most targeted population survey of gun ownership was conducted by Newspoll; the resulting estimate was approximately 2.5 million firearms in 1997, after the gun buyback.

  If that is approximately correct, it suggests that there were about 3.2 million firearms in 1996 and that the buyback led to the removal of approximately 20 percent of the total stock.

  In U.S. terms that would be equivalent to the removal of 40 million firearms

( Note: I skimmed it, it looks more or less okay, several things caught my eye as problematic but the above passage looks pretty ballpark.

Further: I'm having busy days ATM - if I can claw out the time I might loop back to give a longer comment / reply to your upthread question(s) )