In some states you would be fine in others you would end up in jail. I would have to go look at each state to tell you anything for any given state. NY and NJ are out for sure.
But some states state there can not be any ammo attached to the firearm. Is a Side Saddle considered Attached? I don't know.
In some states transporting a long gun in your trunk and stopping can get you arrested.
In states you can have an unloaded shot gun in your trunk I would carry the ammo in a belt made to hold shotgun shells and not attach them to the shotgun unless I was positive about those states laws.
Heck in Ohio having an Unloaded clip fed handgun, rifle or handgun locked in a box and a loaded mag for the firearm loaded in another locked box is considered having a loaded firearm in your vehicle. Go figure.
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