But the primary recoil was caused by the gasses pushing against both the gun and the bullet.
You could see it that way.
In reality, the primary recoil is pressure of the gas forcing the gun back as it forces the bullet forward.
The simpler way is to see it as the bullet is being projected from the gun, which pushes the gun back.
When the bullet is out of the barrel, what are the gasses pushing on then?
Another mass must take the place of the bullet, and that mass can only be the mass of the atmosphere.
Nope. It doesn't really matter what they push against.
The only reason the pushing against the bullet was an issue was because the gas was contained between the bullet and the chamber.
Once that is no longer the case you have the gun being forced backwards by the air pressure, that is all.
There is no need for the gas to push on anything.
So rockets must push on air.
Yes, the "air" which is the exhaust that is propelled from them.
Oh and btw the third cause of recoil is the inrush of atmosphere into the evacuated barrel.
Pure garbage.
The inrush of atmosphere into the evacuated barrel would suck the gun forwards and then stop it.
So you see I was right and all sources were provided, thus rvlvr is a liar.
Nope, you were wrong just like normal.
That would be polite.
You might want to get a dictionary and find out what polite is.