At one time the USAF had a plan to replace its A-10s with F-16s fitted with
a version of the Avenger cannon.  This was tested during Desert Storm, when
F-16As of the 174th Tactical Fighter Wing were fitted with GPU-5 pods on
their centreline pylons, and given the new designation F/A-16A.  The GPU-5
contains the GAU-13 cannon (a four-barrelled version of the seven-barrelled
GAU-8 Avenger 30mm cannon fitted to the A-10) and 353 rounds of ammunition.
If the tests were successful, there were plans for a fleet of F/A-16Cs with
the same armament.

The tests were a disaster.  Precision aiming was impossible for several
reasons:  the pylon mount isn't as steady as the A-10's rigid mounting; the
F-16 flies much faster than an A-10, giving the pilots too little time
approaching the target; the tremendous recoil from the gun shook the plane
around badly; and some essential CCIP (continuously computed impact point)
software was unavailable.  They ended up using it as an area weapon,
spraying multiple targets with ammunition, producing an effect rather like
a cluster bomb.  It took only a couple of days of this before they gave up,
unbolted the gun pods, and went back to dropping real cluster bombs.

The F/A-16C plan was quietly forgotten.  The USAF still has plans to
replace the A-10 with F-16s, but they no longer involve 30mm gun pods (or,
apparently, a designation with an "A" in it).

[Thanks to Kevin Au for posting most of this information]