It's so heavy, 29mm is certainly appropriate.
On 18mm anything short of a D21 or 24 is a joke.

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When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, AGITATION, CHAOS, TURMOIL, FIASCOS, AGGRAVATION, INSTIGATION, NUISANCE-ACTION, and HAVOC !