There are 2 things I do for cold bore accuracy:
1. Clean the bore to white metal clean after every use, followed by dry pre-fouling with a burnishing of tungsten(WS2), before putting the gun away.
2. Cold bore accuracy development, which takes considerable discipline & time.
Precision, and the hot bore
accuracy provided there, can be completely different than cold bore accuracy.
They can be different potentials all together.
For example, I load developed for competitive level precision with a Tubb T2000(tube gun) at 600yds. And the gun performed per it's intended design there. Very good shooter. But I actually bought the gun for varmint hunting, so then I rolled over to cold bore testing.
With a beginning test, I found right off that the gun had zero hunting potential for me. Also, that it would not be worth greater investments to that point.
Basically, I fired 2 shots quick from a cold bore at 200yds, then every 10 minutes fired 2 more. 10 minutes was chosen because every barrel I've ever tested hates a 10min shot rate, and I wanted to see the worst from this gun (how much work was in front of me). It was new brass as well, but that's ok, I can still see what I need to here.
I expected to see was some elongation in a 10sht group. What I got was a walking spread from each 1st shot, with 2nd shots falling into an ugly group, but at least a group.
This gun worked fine for hot bore group shooting(competitive format), but if you see anything like this from a well built
hunting gun, don't waste your time with it in the field.. Get another barrel, cut rifled, and start over.