Playing with Jelly
It is not rocket science. Longer barrels give you more complete propellant combustion which translates to more velocity imparted to the projectile. The more velo, the more energy is carried by the projectile on the impact and the higher ballistic performance. In short, whittle the barrel down and you sacrifice some performance. By way of thinking, the optimal performance for NATO 5.56mm ball, such as M855, is wrung through a 20-inch barrel.
With that in mind, I wanted to check and see just how much velocity dumped by running a 7-inch barrel out of a DB15 I have been testing for the past few weeks.
For reference, the Winchester 55-grain 5.56 NATO FMJ rounds I chose for the bulk of our reliability testing have a listed 3,270 fps muzzle velocity generating 1,305 ft./lbs. muzzle energy. We found that, out of the 7-inch DB15, an average across five rounds hit closer to 2,240 fps, which, using the standard bullet energy formula, translates to something like 619 ft./lbs., or a loss of about a third of its velo and half of its energy.
How effective is that? Well, in 10% gel, the FBI recommends 12-to-18 inches of penetration to be considered an effective self-defense round. In our tests with a 16-inch block of Clear Ballistics 10% gel, I found that every round of a 7-shot test string of Winchester 55-grain FMJ penetrated the entire block and left a significant channel in its wake.
Food for thought. Now to test some Gold Dots and the like to see how they expand.