In the
linked post, you will find:
Mad Mick wrote:...Next comes the tricky part.
If you can't determine the position of the plugs by the slight discolouration of the brass, measure 3.3mm up from the bottom of the lock (Where the key goes), and dead-centre. This is the position of the first plug. WARNING - these plugs are only 2.6mm in diameter and 3.5mm long, so drilling larger/deeper will damage the body/springs underneath. A tip to help in finding the plugs is that they are evenly spaced approx. 3mm on centre. Find the first one and tap it SLIGHTLY with the pin-punch/hammer. Measure 3mm, and tap again. They WILL sink in slightly if tapped enough...
If you use a method similar to the above, you can determine where the plugs are. Using the key (if you have it), measure from the shoulder to the centre of the first cut. (remember, the first cut is the one closest to the bow, and not the tip) Then measure from the first cut, to the second. (this will give the spacing)
Measure from the keyway face (usually flush with the bottom of the lock) up the side where the pins are located, and mark a point at the same length you measured from shoulder to first cut. This should correspond with the plug for the first stack. Mark subsequent points (for the number of key cuts) at intervals you measured between the first and second cuts. Then mark an extra point...this should be the position of the pin holding the plug in place.
I wouldn't go randomly tapping with the punch without first trying to determine a plug position. Since brass is fairly soft, you could end up deforming the lock body over and make removing a plug much more difficult.
HTH.