Since some guns are illegally obtained from legal owners, I'm sure it'd go down a miniscule amount. However, not enough to be worth it.
The only way to remove the supply of A is to remove the demand of A. Why are Betamax VCRs no longer made? Nobody wants one.
When nobody wants a gun, guns will disappear. Short of that, it won't happen. It might go black market, but supply comes from demand.