Here's CJ, one of the students, running the 4+1 Transition Drill with a Tac14 in 20ga. I like this drill because it has many layers to it. The shooter starts at gunbox/cruiser ready and has to get the gun into action. Then they hit both outside targets (long transitions), both inside targets (more transitions), and ends with an emergency load to the center target. With only five rounds, we are practicing numerous skills.
One issue with 20ga shotguns for defensive use is that there is not, in my opinion, a quality defensive buckshot load available for them. One must account for every pellet sent downrange, and quite frankly, I have yet to find a 20ga load with a good enough pattern beyond 7-10 yards to use with confidence.
Here are pics of a Rio (I know) load I asked CJ to test in his gun. I didn't get pics of the Winchester Super X load he also tested, but it was worse. One round was fired at seven and 15 yards with three rounds fired at 25 yards.
Note how many pellets are outside of the body of this large silhouette.
For comparison, here is the same test shot with Federal 8-pellet reduced recoil FliteControl:
I also ran the same test with some Federal "black pack" 9-pellet 00 buck. It held it's own out to 15 yards, but at 25 I had a pellet off of the body and several outside of the effective zones.
