That's what I was thinking, but I read somewhere if you don't get the lead out, it could cause an over pressure. Is this BS?
The real danger is not so much over-pressure, it's that if there's just a little too much lead the bullet can't push it out of the way fast enough and it can blow a ring or bulge in the barrel.
People "shoot the lead out" for years, then they shoot a little more then normal or for some reason there's more leading then usual and they're shocked to see a ringed bore.
A bullet has to push the lead in front of it like the bow wave of water in front of a boat.
If the bullet can't push the lead fast enough, something has to give, and what can give is the barrel gets ringed or bulged.
Also, the bullet does "ride over" some of the lead, and it can iron the lead into a thin plating that's hard to see.
You think the bore is clean, but the steel can corrode under the thin plating of lead, and the first sign of a problem is when a piece of lead flakes off exposing a nice pit in your barrel.
The best tool is a Lewis Lead Remover, and it's the only way to really get the forcing cone clean. You should use the Lewis forcing cone head even if you shoot only jacketed loads, because the Lewis tool also cleans off lead, copper, and carbon from the cone.
The REAL COPPER Chore Boy wrapped around a used bore brush also works, but make sure you buy only genuine Copper Chore Boy. Some other brands are stainless steel with a copper plated finish. These will destroy the barrel.
Stay away from advice to use home brew methods like mixing vinegar and hydrogen peroxide. This removes bluing and when combined with lead forms a VERY toxic chemical that's dangerous.
To clean the chambers of leading, buy a couple of bronze chamber brushes from Brownell's.
These are fast and safe. Usually one pass through a chamber will remove all leading or carbon.