Acetone is a ketone. Amphetamines are amines. Ketones and amines form imines under anhydrous conditions, giving off water.
Why do you all use acetone for making hydrochlorides??
Your amine will react with your solvent, and the water formed in this process will dissolve all salts you get from the remaining amine. Result: an equilibrium between dissolved amine*HCl and imine...
Suggestion: Use diethyl ether, EtOAc or other nonpolar solvent, and simply add enough dried, pre-gassed HCl/IPA (until pH 6.5),
then add 2x the amount of cold, dry acetone and filter off. Voilà.
No need to bother with HCl gas, and you can even keep a small amount of your freebase amine, in case you add too much HCl/IPA: then you can simply revert the reaction by adding small amounts of the free amine, until pH is perfectly in the proper range, and proceed with acetone flooding.
Almost as easy as forming sulfates/phosphates...
indole_amine