Wiping out the barrel

Rifling Impressions

A bullet is slightly larger in diameter than the bore diameter of the barrel in which it is designed to be fired. The bore diameter is the distance from one land to the opposite land in a barrel. As a result, a rifled barrel will impress a negative impression of itself on the sides of the bullet like those seen below.

Very high pressures are generated within a firearm when a cartridge is discharged. These pressures force the bullet from the cartridge case and down the barrel at very high velocities. When a firearm is discharged, the shooter will feel the firearm jump rearward. This rearward movement of the firearm is called recoil. Recoil is for the most part caused by the cartridge case moving rearward as an opposite reaction to the pressures generated to force the bullet down the barrel.

This is why the blood in the barrel couldn't survive a rifle discharge and proves that it was Robin's dna found there after the last shot, the evidence of which (the dna) was located and given by Hentschell. It is the sort of thing I would have thought most people would know but then again twisted sisters are not 'most people,' fortunately. For anybody so bewildered, bullet projectiles are softer than the rifle bore which why if found intact will have signs of 'rifling' or characteristics of the particular firearm they were discharged from. The generated heat, velocity, the suppressed fit of the bullet inside the barrel all contributed to the reason why the dna was placed there after the last shot drawn in both by vacuum temporarily created in the barrel by the discharge and the back pressure escaping from the wound to Robin's head.