Now what stim was "black beauties" referring to? Guessing it was one of HCl salt...D-meth-HCl? D-amph-HCl?... Assuming it was D-_ youd want to titrate up the Dl dose to equal the central effects. Due to the L offsetting the ratio of central-to-periphial effect, don't ever expect it to feel exactly the same unless the L is removed (within reason practically impossible so don't bother). The salts in Adderall are all heavier vs. HCl so take the freebase weight and add equimolar HCl weight to that compare more accurately the an HCl, then compensate by assuming L has about 1/4 the central effect and that it takes up 1/4 the base weight... The 3 XRs were what mg each? Comparing to what mg black beauties? If it was D-amph/D-meth-HCl, theres probly about a 2-fold central-effect advantage to the latters. Be aware twice the amount XR would have FAR more non-central effects in contrast and >100mg w/out tolerance likely severe and possibly including though not limited to anorexia, insomnia, tachycardia, hyperthermia, periphial blood flow loss...
As for the in situ- take LDs advice...def not a good idea
You could AB it the right way at the expense of suffering severe mechanical lossiness - this a given for any amount thats not going into the gram-range (in terms of the base or expected HCl-salt weights). BTW skill/effort, solvents used, and adaquate equip is necessity or decent/reasonably pure yield would not even be seen regardless!
