The rule may come from the 60's but so does the 2N2222.The rule of thumb is that for hard saturation, the base current should be 10% of the collector current. But this rule comes from the 60's, when the average transistor had much less gain, and the gain dropped off rapidly at higher collector currents. Today's parts are much better, so for a small signal transistor with a typical gain of 100, I start with 5% base current.
Queue the comments about why anyone would use an old obsolete part when more modern transistors are available
True, but it was an exceptional part at the time, the main reason it imprinted on an entire generation of designers. Also, the 2n3055 is of the same vintage and had a worst case gain of 20.
<Off Topic>Whenever this part comes up I would be remiss if I failed to mention the time I was called in to fix the SSN 774 Virginia after the first sea trials to replace some 2N2222's that failed for excessive sat voltage.
Seems the Mil Version Jan parts do not have a spec for sat voltage, and normal production runs can get quite high. We had to screen for this as the build was qualified and hence locked in stone.
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