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Back in the 1940s, it was common to cover gun ports with tape. As well as improving streamlining, it would presumably help keep them clean.

Spitfire Mk 1 Spitfire Mk 1, with all eight .303 inch Browning machine guns covered (source)

I suggest it would be fairly straightforward to design a fairing that would immediately disintegrate if the gun were to be actually fired; but, while not in use, prevent ingress from anything unwanted, and provide a small boost to aerodynamic efficiency.

M-61A1 cannon mounted on the F15 Eagle M-61A1 cannon mounted on the F15 Eagle (source)

F-16 M61 Vulcan 20 mm cannon F-16 M61 Vulcan 20 mm cannon gun port (source)

It's not like these guns are getting regular use. A fairing would seem to deliver a benefit at little cost. What is the reason they're not more common?

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It depends on the airframe. Older fighters from the 1950s-1980s typically faired the gun(s), but left the muzzle exposed. I suspect the parasite drag from this was minimal in comparison with that created by external stores such as fuel tanks, missiles, bombs, pylons and weapon racks, etc.

Newer fighters such as the F-22A and F-35A, with requirements for very low frontal radar cross sections, do actually use fully enclosed internal guns with a fast acting, faired door over the muzzle. This actuates to allow the gun to fire, then closes quickly after the trigger is released.

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Because the guns are used. In training, fighter aircraft with an air-to-ground mission probably exercise Air-to-Ground deliveries, (including what is called Low-Angle Strafe) several times a month. At least they used to when I was flying F-4s. I would be surprised if it was any less nowadays.

Air-to-Air tasked aircraft (like F-15s or F-22s) may do Air-to-Air gunnery (against a towed target, (we called it a dart back in the day), less frequently. I don't believe these are still in use, they use towed acoustic sensor targets these days. But live fire Air-to-Air gunnery is still done often enough to not make it worthwhile to cover the Gun ports.

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Finally, if they did cover the gun ports, and then shot bullets through the covers, there would be the additional hassle of cleaning out all the debris from the gun ports after the aircraft landed.

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  • $\begingroup$ Re "Finally, if they did cover the gun ports, and then shot bullets through the covers, there would be the additional hassle of cleaning out all the debris from the gun ports after the aircraft landed." -- I'm having trouble following. Surely the instant the gun is fired, most of the cover is blown away and it's essentially as if it was never there-- assuming we're talking about a "cover" that is more or less equivalent in its bullet-resistance to the pieces of tape in the photo included in the question-- $\endgroup$ Nov 2 at 19:42
  • $\begingroup$ I'm not sure, but I suspect that at 350-450 kias+, the dynamic pressure would be pushing any remaining fragments into the opening the gun barrels were sticking out of. $\endgroup$ Nov 2 at 19:54
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    $\begingroup$ @CharlesBretana The gas coming out of the muzzle during firing is likely going over 1000 knots. The ambient air is not likely to push much back in to the barrel. Even if it could, there cannot be any flow through the barrel because the breech is in the way (unless you have some weird recoilless rifle setup upload.wikimedia.org/wikipedia/commons/c/c3/…). $\endgroup$ Nov 3 at 0:49
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    $\begingroup$ I haven't done a complete analysis of this, so I confess my starement is based only on intuition, and might be wrong, but a complete analysis has to consider that the gun gases are only coming out of the muzzle of the gun, which is a considerably smaller cross section of the total area that needs to be covered, the total mass-flow, and momentum, would therefore be equally different. $\endgroup$ Nov 3 at 13:15
  • $\begingroup$ Just FYI, RAF fighters gun ports were re-patched as part of the re-arming process between sorties - 36 minutes 53 seconds into this video - youtube.com/watch?v=0rhGrPBDhEA $\endgroup$ Nov 4 at 23:19

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