For new track construction, the procedure is usually as
follows: The ground is graded. the ties and track are
laid on the bare graded ground. Once the track is spiked,
a ballast train is brought onto the new track and dumps
ballast.

A ballast regulator does some preliminary shaping of the
ballast and a tamper then comes in to work the ballust
under the ties.

Tampers and ballast regulators often work as a paired set,
with each making multiple passes as each does its part
to shape the ballast and align the track.

Ballast regulators not only shape the contours of the ballast,
but, depending on which blades are lowered, can move
ballast from the shoulder to between the tracks or from
between the tracks to the shoulder, as needed.

You can see photos of both types of equipment, including
a close-up of the tamper head working ballast under ties
on my railroad construction page here:

http://www.robl.w1.com/pix-rrc/index.htm

-- Ernest