Beveled Holes and Rounded pins  

Some lock manufacturers (e.g., Yale) bevel the edges of the plug holes and/or round off the ends of the key pins. This tends to reduce the wear on the lock and it can both help and hinder lock picking. You can recognize a lock with these features by the large give in set pins. See figure 9.4. that is, the distance between the height at which the driver pin catches on the edge of the plug hole and the height at which the driver pin catches on the edge of the plug hole and the height at which the key pin hits the hull is larger (sometimes as large as a sixteenth of an inch) when the plug holes are beveled or the pins are rounded. While the key pin is moving between those two heights, the only resistance to motion will be the force of the spring. There won't be any binding friction. This corresponds to the dip in the force graph shown in Figure 5.5.

A Lock with beveled plug holes requires more scrubbing to open than a lock without beveled holes because the driver pins set on the bevel instead of setting on the top of the plug. Thge plug will not turn if one of the drivers is caught on a bevel. The key pin must be scrubbed again to push the driver pin up and off the bevel. The left driver pin in Figure 9.6a is set. The driver is resting on the bevel , and the bottom plate has moved enough to allow the right driver to bind. Figure 9.6b shows what happens after the right driver pin sets. The bottom plate slides further to the right and now the left driver pin is scissored between the bevel and the top plate. It is caught on the bevel. To open the lock, the left driver pin must be pushed up above the bevel. Once that driver is free, the bottom plate can slide and the right driver may bind on its bevel.

If you encounter a lock with beveled plug holes, and all the pins appear to be set but the lock is not opening, you should reduce torque and continue scrubbing over the pins. The reduced torque will make it easier to push the drivers off the bevels. If pins unset when you reduce the torque, try increasing the torque and picking pressure. The problem with increasing the force is that you may jam some key pins into the hull.

Figure 9.3: Driver pin wider than key pin

Figure 9.4: Beveled plug holes and rounded key pins

Mushroom Driver Pins

A general trick that lock makers use to make picking harder is to modify the shape of the driver pin. the most popular shapes are mushroom, spool and serrated, see Figure 9.7. The purpose of these  shapes is to cause the pins to false set low. These drivers stop a picking technique called vibration picking (see section 9.12), but they only slightly complicate scrubbing and one-pin-at-a-time picking (see chapter 4).

Figure 9.5: (a) Driver sets on bevel

Figure 9.6: (a) Driver jams on bevel

If you pick a lock and the plug stops turning after a few degrees and none of the pins can be pushed up any further, then you known that the lock has modified drivers. Basically, the lip of the driver has caught at the sheer line. See the bottom of Figure 9.7. Mushroom and spool drivers are often found in Russian locks, and locks that have several spacers for master keying.

You can identify the positions with the mushroom drivers by applying a light torque and pushing up on each pin. The pins with mushroom drivers will exhibit a tendency to bring the plug back to the fully locked position. By pushing the key pin up you are pushing the flat top fo the key pin  against the tilted bottom of the mushroom driver. this causes the drive rto straighten up which in turn causes the plug to unrotate. You can use this motion to identify the columns that have mushroom drivers. Push those pins up to sheer line; even if you lose some of the other pins in the process they will be easier to re-pick than the pins with mushroom drivers. Eventually all the pins will be correctly set at the sheer line.

One way to identify all the positions with mushroom dirvers is to use the flat of your pick to push all the pins up about halfway. This should put most of the drivers in their cockable position and you can feel for them.

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