Full wadcutters frequently have problems reliably feeding from the magazines of semi-automatic pistols, so SWCs may be used when a true WC is desired but cannot be used for this reason.
[1] The semiwadcutter design consists of a roughly conical shape with the tip truncated flat (called a meplat), sitting on a cylinder (A at right).
The SWC design offers better external ballistics than the wadcutter, as its conical nose produces less drag than the flat cylinder.
A typical modification is to alter the conical section to make the sides concave, to reduce the bullet mass, or convex, to increase it.
Because of the three wide equal width driving bands, the total bearing surface is greater than half the overall length of the bullet.
This large bearing surface helps the Keith-style SWC to be an inherently accurate bullet, and minimizes leading from gas blow-by.