The internal gun you refer to is in the F-4E. 6,000 rounds per minute of 20 mm is quite impressive. In the "E" model, a pilot with a light touch on the trigger could plan on three, two second bursts before the gun was empty. During strafing runs on the range, pilots would bet on who could get the least number of rounds out of the gun on each pass. As soon as the electrical connection was made with the trigger, the gun wold spin up very quickly. So, it was a matter of just tickling the trigger.
The AIM-7s have great capability, but with any complex weapon many things can go wrong. Once, when firing an AIM-7F the missile launched with a loud whoosh but disappeared and didn't come out front where it should have. So, like a tree full of owls, we were looking all over for it. We suddenly saw it coming from low left and out front of us in a slow barrel roll. With its fuel exhausted, it rolled over and vertical nose down beyond a cloud deck at low level. I stroked the burners to MAX to run it down and see what it was going to do next. Just as we crossed the cloud formation, the missile speared the ocean about a quarter mile short of a couple of Phillipinos in their banca boat.
After RTB in the debrief, our chase jet guys said the Sparrow separated, lit off, dove down with a hard right turn toward them, which they almost did a defensive break turn for, and continued in a huge barrel roll over the top of us to the left. As it continued rolling back up, that was where we spotted it. Of course the powers to be assumed we had screwed up something with switchology and/or didn't have a radar lock. Since this was the first "F" fired off an F-4 in PACAF, it had a telemetry package installed. The results showed perfect switch positions and a solid radar lock. As it turned out, the weapons loaders didn't engage two of the four main body steering fins during the load process. So, when it came off the jet, the two interconnected fins went to full deflection in the slipstream while the other two were attempting to steer the missile normally. Hence, the impressive barrel roll and near kill on a banca boat, not to mention a near miss with our chase.
So, the option of stepping in the phone booth for a knife fight was always the most reliable option.