I hope you find its ok. . my nephew left a HW80k in the barn and it had rust in the barrel.I used some penetrating oil tht we used at work (Freeway https://www.amazon.co.uk/L-S-Enginee.../dp/B0051NSFPS ) and a cheap airgun cleaning kit.
It worked out ok for that barrel.
It's a bit of a risk to be honest because I'd have to get it grafted onto a gun just to test it so I'll probably not bother.. I'll see when I get it..
"corners should be round" Theo Evo .22/.177 - Meopta 6x42, DS huntsman classic .20 vortex razor LH 3-15x42 under supervised boingrati tuning by Tony L & Tinbum, HW77 forest green - Nikon prostaff 2-7x32 plex.