Nice pussy cat ya got there RS, ... mine just defacates and urinates willy nilly about the place.
OP,
The thing with those old Mil bores, they rarely if ever, saw an agressive bore cleaning. The armourer's had ammonia, yes, but not the grunt's, so all those rounds fired built up layer apon layer of carbon and jacket fouling(old cupro-nickle being the worst to get out). Imagine the layers of an onion skin. Carbon/jacket/carbon etc..
Brake cleaner helps strip the carbon so the underlaying layer is exposed to solvent.
It can take many, many repeat's to get an ammonia patch to come out not blue stained.
Flood the bore with brake cleaner, let it sit muzzle down a few mins., brush a few strokes, patch.
Flood with aggressive copper cutter, let sit, brush and patch.
Repeat.
Repeat.
^
^
^
If cupro fouled, bore paste with a tight patch between the above steps.
When no blue shows, and the rod feels even resistance as you push ... your done.
Dont get either chemical on the gun's exterior.
How bad can fouling get?, one old 6.5mm, made in 1899 Swede was fouling constricted a full 2.5 thou. in the first inch of the barrel. It overpressured and expanded Lapua primer pockets with(dismally inaccurate)
mild starting loads. The bolt was hard to lift.
Dozens of the above cleanings exposed a good bore that now shoots 5/8th's MOA, and with 5 grains more R22 in the case, to normal pressures.
Concentrate on bedding and the bore, they shoot well when they're in the good shape you described yours as being.