(2) If the defendant, other than a defendant subject to subsection (a)(1), (a)(2), (a)(3), (a)(4), or (a)(5), possessed all ammunition and firearms solely for lawful sporting purposes or collection, and did not unlawfully discharge or otherwise unlawfully use such firearms or ammunition, decrease the offense level determined above to level 6.
(3) If the offense involved—
(A) a destructive device that is a portable rocket, a missile, or a device for use in launching a portable rocket or a missile, increase by 15
(B) a destructive device other than a destructive device referred to in subdivision (A), increase by 2 levels.
(4) If any firearm was stolen, or had an altered or obliterated serial number, increase by 2 levels.
The cumulative offense level determined from the application of subsections (b)(1) through (b)(4) may not exceed level 29, except if subsection (b)(3)(A) applies.
(5) If the defendant used or possessed any firearm or ammunition in connection with another felony offense; or possessed or transferred any firearm or ammunition with knowledge, intent, or reason to believe that it would be used or possessed in connection with another felony offense, increase by 4 levels. If the resulting offense level is less than level 18, increase to level 18.
(6) If a recordkeeping offense reflected an effort to conceal a substantive offense involving firearms or ammunition, increase to the offense level for the substantive offense.
(c) Cross Reference
(1) If the defendant used or possessed any firearm or ammunition in connection with the commission or attempted commission of another offense, or possessed or transferred a firearm or ammunition with