Bullet Lubrication
 
Lead and lead alloy bullets require lubrication to prevent leading. In general higher velocities require harder alloys. Lubrication allows softer alloys to be shot at higher velocities without leading, but in general some lubrication is used at all velocities.
Cast bullets, especially those for black powder have traditionally used "grease grooves" to provide lubrication. Cast bullets for black powder also tend to have larger grease grooves than those intended for smokeless powder. The lubes used for black powder also are usually non-petroleum based. The lube not only lubricates the bullet providing a gas seal but also aids in keeping fouling soft .

Swaged bullets also require lubrication for the same reasons. In casting the mold is hinged and grease grooves are a natural way to hold lubrication. In swaging a "core" a slug of lead or lead alloy is placed in a die with a top and bottom punch and the punches are driven together and  the alloy is put under 10,000 to 40,000 psi and the alloy flows to fill the die.
 In theory a die can have grease grooves cut in it. The problem is that once you applied the force the bullet could not be removed. A method that does not lend itself to production. There are several options for lubricating swaged bullets.
 
Base Guard Front View Base Guard Bottom View Base Guards
Base guards are copper discs in the shape of a cone with a hole in the center. Inserted in a swaging die the cone flattens and fills the die with the alloy core filling behind it. A "rivet" of alloy flows through the base guard and into a space behind the base guard in the die bottom punch.

The base guard works as a gas check. Using lead bullets velocity is limited to 900-1000 fps. Using black powder it depends on your gun how effective it is. Alloys harder than BHN 8 (30:1) have problems with rivet formation
 

Knurl Lube
A bullet is swaged and then knurled. This creates thousands of small pockets to hold lube. The bullet is then lubed using a BP lube (SPG) or a monomolecular wax can be used (Corbin). The bullet is then swaged to size, trapping the lube. In either case leading is prevented past 1350 fps. (in my rifle).

The bullet has lube throughout it's driven length. A simple and effective alternative to grease grooves. I have shot a group size of .6" with this design (100yds)
 

Knurl Lube Black Powder
A bullet is swaged and then knurled. This creates thousands of small pockets to hold lube. The bullet is then lubed using a BP lube (SPG) or a monomolecular wax can be used (Corbin).
This design uses the "bump up" of BP to expand into the rifling. It can be used as a bore rider as the knurls are ± .01and are "soft" enough to be pushed into the rifling. This has had limited testing, but has shown reasonable groups.
   

Examples of Bullet Types

Semi-Wad Cutter Style
 

Semi-wadcutter bullets are characterized by a slight flat portion where the ogive transitions to the the body of the bullet. This originally was a feature of target bullets to give clean holes in paper targets. In swaged bullets it is a manufacturing feature. It results from the swaging process itself. The lead is swaged in the die between two punches. Typically the nose punch is on the bottom but in any case no punch can go to zero thickness. In this case the nose punch must have sufficient steel at it's opening to support it's shape. In practice this opening can only be machined so small and still resist the forces involved in the swaging process and have sufficient mechanical integrity.