I reckon BS, the Brococks had all of the bits needed to fire a centre fire primer, most BB revolvers do not. They also had a rifled barrel of the correct calibre for the most common round on earth that from what I can remember was over engineered. Likewise the quality of the guns was far higher than any of the BB revolvers around today, as others have said they are of pot metal castings and the barrel is .177 calibre and incredibly thin.
With the level of work needed, if you can engineer one of these revolvers to fire a live round then you would be capable of making your own firearms anyway so banning them would be pointless.
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