If you want more than an explosive fizzle, you must have a neutron emitter (aka trigger/initiator).
Unless you are making a Hollywood movie. In which case, carry on.
For a quick start of the chain reaction at the right moment a neutron trigger / initiator is used. An initiator is not strictly necessary for an effective gun design [1] [2], as long as the design uses "target capture" (in essence, ensuring that the two subcritical masses, once fired together, cannot come apart until they explode). Considering the 70 spontaneous fissions per second this only causes a delay of a few times 1/70 seconds, which in this case does not matter. Initiators were only added to Little Boy late in its design.
http://www.cartage.org.lb/en/themes/Sciences/Chemistry/NuclearChemistry/NuclearWeapons/FirstChainReaction/FirstNuclWeapons/LittleBoy.htm
You are WRONG. Guns do NOT need initiators!
If you want more than an explosive fizzle, you must have a neutron emitter (aka trigger/initiator).
Unless you are making a Hollywood movie. In which case, carry on.