Someone will recommend cleaning with hot soapy water. And that will do the job wonderfully, but is not an absolute necessity.
I don’t think it needs to be hot. Maybe not even soapy.
But I would at least run 2 or 3 water soaked patches thru the bore and chamber area, or some of the old type Rifle Bore Cleaner that the US and other military organizations have used for cleaning for about 100 years. It is still available. ( Must have at least a 50 year shelf life ).
You can test for mercuric primers by taking a cartridge out and pull the bullet and dump the powder. Find a flat piece of steel that has no traces of paint, oil, plating, etc. on it. If it is rusty, brush it down to shiny metal with a dry, clean wire brush. Now put the still primed empty hull in the chamber. Place the muzzle of the barrel almost right against the steel, and pop the primer. It will leave powdery residue on the plate. Take the plate in out of the weather, and check the primer residue deposit every day for a week for new corrosion or a green acidic looking color. Either one of those things means corrosive primers. If nothing changes, the primer was not mercuric/corrosive.
Go through your ammo and see if they all have the same date and / or manufacturer’s code head stamp. If they are not all the same I would test at least one round out of every different head stamp or lot number.
During WW I, WWII, and Korean War you can bet the farm that the troops rarely had access to hot water in the field, so that when they needed to clean a gun, they used the old Rifle Bore Cleaner or cold water on cotton patches, with good results. The water will remove the salts.
If your rifle has a chromed bore, that is good protection against rusting from the use of mercuric primed ammo. That’s why most post WWII Eastern Bloc military rifles had chromed bores.