Rheinmetall Mk20 20mm S20 Naval Gun in slow motion
This video shows an Hellenic Navy Rheinmetall Mk20 with S20 Naval Gun Mount firing in slow motion. Note how the barrel appears to recoil. At first glance it appears that the gun utilizes a short recoil action like the Rheinmetall MG3 and the MG42. It is actually gas operated but the whole barreled action is mounted on a recoiling platform in order to soften the recoil.
[ Many thanks to Aegeanhawk for the video. ]

I think he made a “funny.” Or in other words, JOKE.
@ Mate: “Man-portable”? As in “AUTOMATIC” fire?
I don’t think the “man” to carry that has been manufactured yet! Maybe in 200 years? As per Cyborg?
No – the least powerful 20mm ammo in service in an automatic cannon today is the 20×82 round originally developed for the Mauser MG 151/20 aircraft gun in WW2. The gun and ammo are both still made in South Africa as the Vektor GA-1, but the gun weight is around 40 kg (88 lb) – that’s just for the gun, without any sort of mounting.
Are there any kind of man portable 20mm machine guns?