My first though would be the ammo itself. If the hangup is that the rounds are not fully seating I would check that the bullets are not seated out too far. Also would check for proper sizing of the bullets and if they were ok would then try a Lee factory crimp die. Check for high primers too. You don't mention the brand or model of pistol or if the ammo is factory or reloads but I would avoid the reamer until I knew for sure that the chamber was the problem.