Other firearm evidence that can be found at the scene of the shooting includes pellet and pellet cleats; these may indicate the caliber of the shotgun. Wads and pellets can be collected and preserved in the same way as bullets and cartridges. The bullets are tracked by rifling the bullet to the gun and then indenting the firing pin into the spent projectile. So, if you're firing a rifled bullet, it could be traced back to the barrel and the worn case to the firing pin, but normal shotgun pellets can't.
Depending on the size, pattern and count of the shot, I suppose I could probably determine the caliber of the weapon (possible, and sure if retrieving the cue) and perhaps the choke (less likely). Part of that would also come from information from the scene of the shooting, such as the distance of the gun to the target. The recovered shotgun helmets could be related to the weapon. The type of shot (lead, steel, some other non-toxic shot) may be related to recovered helmets, since helmets are usually marked with the type of shot they contain.
Pellet and pellet (in addition to other pellets) do not have unique marks of having been fired from a smooth-bore barrel, or even from a rifled barrel. Rifled bullets fired from smooth-bore barrels have *some* degrees of unique markings on smooth-bore barrels and a*definite* degree of unique markings on rifled barrels. The sabots also have a definite degree of unique markings on the fluted barrels. The ability to effectively monitor arms transfers and track firearms and ammunition remains a key security challenge for the 21st century.
The marking of firearms and ammunition contributes to effective tracing by enabling identification and efficient record keeping. UN regulations provide a coherent framework of requirements for the marking of firearms, but the lack of globally accepted standards for the implementation of such requirements challenges the effectiveness of international cooperation in tracing. The use of “smart technologies” can help overcome some of these challenges, but only if they are supported by a specific regulatory framework. Basically, shotguns are often chosen as killer weapons because of the reduction in forensic evidence, and double-barreled clipped shotguns are especially useful because they don't automatically eject a projectile to accommodate a new one, you just pull the trigger again.