Dist.Ct. did not err in dismissing defendant’s section 2241 petition that challenged his 44-year sentence on charges of mailing explosive devices and possessing and using destructive device in furtherance of crime of violence under section 924(c), where defendant had previously been unsuccessful in filing motion for new sentence under 28 USC section 2255. Section 2255(h) provides only limited second and successive federal habeas corpus motions, and both parties agreed that defendant did not meet either of two exceptions that authorized second section 2255 motion. Moreover, defendant could not use “savings clause” under section 2255(e), so as to allow him to file instant section 2241 petition, because new case that would have supported reduction in his sentence, i.e., Dean, 137 S.Ct. 1170, did not apply retroactively on collateral review, even though: (1) Dean overruled existing precedent (that was relied upon by sentencing court) that precluded Dist Ct. from considering defendant’s section 924(c) 30-year mandatory minimum sentence when sentencing him for other offenses; and (2) sentencing court wanted to give defendant lower sentence.