Get an old copper brush wrap with 000 steel wool
DONT USE OIL , let wool do its job, you wont hurt the gun
At all, run through bore with the rifling Fir a few mins
At a regular speed as if you were cleaning with solvent
Take the brush off, then run patches doused in
A penetrant like rust check in red can
I use the green can rust check for long term storage
It turns greasy / waxy and resists moisture bigtime
Once you run the rust check and patches through bore
Dry it and steel wool it again but use the rust check on
The brush this time, ive cleaned Nd saved dozens of
Guns for people who had fired corrosive ammo Nd no
Cleaning afterwards, inhad an 8mm mauser here a guy
Fired 1000 rounds of turkish ball ammo through and never cleaned
He figured it was toast, bore dark Nd frosted
I did what i explained in this post and got the barrel back
To pretty well the cond it was in prior, but took some
Time/ patience and elbow grease