Barrel Leading?

[metweezer]

Why will a tight boolit not lead up the barrel of a pistol but a loose boolit will? I would think that the friction of a lead boolit making contact all the way through the barrel would leave more lead behind in the barrel.

[fishnbob]

The tight boolit will obturate under the pressure of the gas formed by the burning powder and seal off the sides as it travels merrily along the barrel. The thought is, if the barrel is not sealed, then the hot burning gases pass by the boolit, burning and melting slivers of lead off the sides and that is deposited in the barrel.

[noylj]

The tight bullet has lube to prevent leading.
A loose bullet suffers severe gas cutting and hot gases ruch through the small gap and melt off lead quickly.

[462]

Vaporizing, rather than melting, is the correct term.

[Bret4207]

Think of it this way, the barrel on most guns is fairly uniform inside. The boolit is "sized" in the barrel as it enters the leade. Once it's there it's pretty much the size it'll be through the trip up the bore. Plus there's a film of lube (hopefully) between the bore surface and boolit. So it's not like the boolit is scrubbing along the bore abrading away.

As was mentioned, smaller boolits let the gases flow by and errode the boolit sides, vaporizing the lead alloy and often depositing it in the bore as the "leading" we see sometimes. THere are other reasons for it too, but with and undersized boolit that seems to be the main one.

[geargnasher]

Like Bret said, lead doesn't really "rub off" in the barrel unless there's a really rough spot somewhere. Most all common leading is due to poor boolit fit or an imbalance in the load somewhere (alloy/powder/lube/etc.) causing gas blowby around the boolit. The lead abrades or "gas cuts" just like a water jet cutting steel. Once a leak starts, it's like a dam breaking and the leading adds up.

One more thing, if there is even a TRACE of copper fouling in the barrel, lead will rub off and stick to the copper and accumulate rapidly, so be sure and remove the copper before shooting cast.

Gear