Randy, a rifle with a 10.5" barrel is a SBR and you must register it with the ATF and pay a $200 tax. I have a feeling you're talking about an AR15 'Other', which is not a rifle or a pistol. Usually, on an other with a 10.5" barrel, the muzzle device must be welded on to make the overall length. Or it can have a 12.5" barrel without having the muzzle device welded. No registration or tax stamp required on an 'Other". See the video "What is an Other?" here >>> stagarms.com/products/stag-15/other/stag-15-other-12-5-5-56mm-nitride-rh-black-na.html

Randy, yes Sir, it is legal as long as it has no Shoulder Stock or a Brace as shown here : budsgunshop.com/search.php/q/ar+pistol -------------- If it has a Shoulder Stock and less than 16 inch Barrel it would be considered an SBR (Short Barreled Rifle) and would be required to be registered as an NFA Firearm and $200 Tax Stamp paid. Cheers and stay safe!