"We conclude that GBPs are an ineffective policy strategy to reduce gun violence, a finding consistent with descriptive evidence that (i) firearm sales prices are set too low by cities to appreciably reduce the local supply of firearms, (ii) most GBP participants are drawn from populations with low crime risk, and (iii) firearms sold in GBPs tend to be older and less well functioning than the average firearm.

Why do we even have gun buy back programs in America where guns are legal? It's a stupid concept and this paper confirms this.