As we known, mercurium fulminate was discovered in 1800 by Howard. But some years before, french chemist Berthollet discovered the uses of silver fulminate. My idea is having a wealthy patron, the Duke of Orleans, Colonel General of the Hussars, gathering a team of "household scientists" in order to create a new carbine : Berthollet, former physician of the Orleans household, Lepage (who created a percussion lock in 1807 OTL), armorer of the Orleans household, and Lavoisier, still Director of the Powder and Salpetrae Administration, with ancient links to Orleans. OTL, the new hussars carbine was the model 1786. Is it possible to have a working percussion lock carbine by the end of the 1780' ?