Zorn, the oral bioavailability of methamphetamine is about 70%. I haven't found any data for other amphetamines
Cook CE, Jeffcoat AR, Sadler BM, Hill JM, Voyksner RD, Pugh DE, White WR, Perez-Reyes M.
Pharmacokinetics of oral methamphetamine and effects of repeated daily dosing in
humans. Drug Metab Dispos. 1992 Nov-Dec;20(6):856-62.
Cook CE, Jeffcoat AR, Hill JM, Pugh DE, Patetta PK, Sadler BM, White WR,Perez-Reyes M.
Pharmacokinetics of methamphetamine self-administered to human subjects by
smoking S-(+)-methamphetamine hydrochloride. Drug Metab Dispos. 1993;21(4):717-23.