Your combination is fine. To be a legal shotgun the barrel must be 18" or longer AND the overall length has to be 26" or longer. Less on either dimension is a NFA SBS.
The mention of the 14.5" version as "firearm" above is legal at federal level only if the gun came from factory with a pistol grip and never had a buttstock installed.
Oak Point, TX 75068
$20 firearm transfers ($15 with CHL/LTC)
$50 NFA transfers
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