I grew up shooting. Rifles, pistols, bows, you name it. If it shot something, I shot it. At one point, before a tragic fishing accident took the 20/20 vision in my right eye*, I was headed for Nationals in the Junior Olympics with my brother to compete in small bore .22 caliber.
In shooting, both barrels refers generally to shooting skeet -- with a double-barreled shotgun. These kinds of shotguns have a 2-barrel configuration that are either over/under or side-by-side. Both barrels released at once is a helluva shock to your shoulder. And if your shot is even remotely close to the clay pigeon, you'll obliterate it!
In our dental offices, we have to go at every day with both barrels blazing. We have to use every resource we have every day to make sure we're successful. (I use that same term for chewing someone out that has it coming; they might get it with “both barrels.”)
As an example: If you have a celebrity in your practice - local or national - you should be forever parading that relationship around for all to see. This is using both barrels. It’s powerful.
Celebrities attract eyeballs to messages. They attract readership because they are fascinating and interesting. Why is the Kardashians' enterprise worth $120MM a year in business? Because it is their business to be interesting and fascinating. It's like a salt lick for deer. It's BAIT for readers to respond to.
To understand why we’re so interested and intrigued by celebrities (this goes wayyy back, by the way, it’s nothing new), read the book by Sally Hogshead, Fascinate. It's instructive in many ways and a great marketing book, too.