Its development was abandoned when it was discovered that the spontaneous fission rate of nuclear reactor-bred plutonium was too high for use in a gun-type design due to the high concentration of the isotope plutonium-240 in the plutonium produced at the Clinton Engineer Works.
The development of this project was halted due to the high concentration of plutonium-240, which is a byproduct of nuclear reactor-bred plutonium, and its impact on the gun design's functionality.