Wadcutters:
There are two types of wadcutters--cast and swaged.
In general, 99.9% of cast wadcutters will be button-nose (see attached) or double-ended wadcutters (same on both ends so it doesn't matter which way you load them). They do NOT have a hollow base. These are made by pouring molten lead into a mold, letting it harden slightly, and dumping them onto a towel to finish cooling. These are great general purpose wadcutter bullets and can be loaded to peak .38 Spl pressure.
EVERY swaged wadcutter (see attached) I have ever seen has been a hollow-base wadcutter. These are made by the lead being cold swaged in a mold, and tend to be as consistent dimensionally and in weight as jacketed bullets (with no jacket to interfere with the manufacturing) since they are made the same way.
The current swaged bullets tend to be made from 96/4, 95/5, 94/6, or 92/6/2 lead alloy and are NOT as soft as many think they are. However, the HBWC has a great weakness—while they tend to be much more accurate than the solid cast wadcutters due to the HB, that HB also makes them quite weak. In .38 Spl/.357 Mag applications, you just can't take them above 800fps without risking the skirt (the HB section) separating from the rest of the bullet and either you get two holes in the target or you get the skirt left in the barrel as a barrel obstruction. The pressure that opens the skirt section to seal the bore also means that there is a lot of friction/drag along the skirt and too much will pull it from the rest of the bullet.
For this reason, DO NOT load HBWCs over 800fps.
Seating:
Factory ammo has the bullet meplat seated just slightly below flush with the case mouth and a slight roll crimp applied (see attached). Reloads for a semi-auto .38 Spl must be loaded this way.
For revolvers, you can load them like this, or you can load them with the bullet extending from the case slightly. In the cast wadcutter picture attached, you can see the button-nose, shoulder, the crimp groove, and three lube grooves. Old NRA testing shows that best accuracy is with ONLY the bottom lube groove filled with lube.
In all cases, if real target accuracy is your goal you must:
1) NOT swage the bullet down during seating (pull bullet after seating and if it is smaller in diameter than was originally, you need to expand the case (NOT flare the case mouth) more and probably need a larger expander plug.
2) Flare the case mouth enough that the bullet is seated about 1/4-1/3 of the way in the case to start with so the bullet can NOT tip during seating. You are pushing a "loose barge" from the rear and need all the control you can get.