I mean, from my compromise I suggested, the guns before nerf will be sold to the players at the old price and their guns stats will not change. After the nerf, guns bought from that day on will be sold at a lower price - and of course its stats will be different from the gun before it was nerfed.
I am not saying that after nerfing all guns of one type that the price is lowered. This will definitely cause players to demand a refund for the excess they paid when they bought it.