Not in the US that I know of, though it is restricted in nations that have outlawed other arms.
The reasons would be numerous:
1. The name, it implies a hunting function.
One of the key successful avenues the antis had in the past was divide and conquer of firearm owners and "sporting" terminology and requirements.
Even though the 2nd Amendment had nothing to do with hunting, for several years there the antis had many convinced that the most legitimate purpose of firearm ownership was hunting.
This enabled them to attempt to minimize or eliminate ownership of everything not necessary for hunting.
It would be counter productive to start targeting "buck" or "deer" shot with such a strategy. With a "buck" being a male deer. When dealing with emotional illogical arguments name recognition and terminology can mean more than facts, and buckshot sounds a lot like a hunting round.
2. Gun control is typically about control, not the reasons it is sold to the public. Government fears buckshot less than many other projectiles. Even though it is one of the deadliest close range loads.
The reason for this lack of fear is modern body armor, range limitations, and various ballistic protections on buildings, vehicles, etc of those in power.
Buckshot penetrates worse than many .22LR rounds per pellet, and is easily defeated by things worn by most LEO/military.
So while it may be one of the deadliest things up close to unarmored civilians, it is one of the least feared by governments. They can afford to come back to it much later long after many other things have been restricted.
Shotguns are one of the final things they go after.
In places that have drastically restricted most semi-auto firearms, centerfire rifles and most handguns, they can keep track of and limit who buys buckshot, even having amount per year quantity limits allowed specifically for hunting.
3. In line with reason number 2, gun control as with many things is actually more "effective" (at disarmament and reducing potential effective resistance) when all things are not actually banned, but rather progressively restricted.
If you ban all guns for example those guns that people do acquire will be whatever is most convenient or desired, whether they are short barreled shotguns or select fire weapons.
If on the other hand you make those you fear the least less restricted and more obtainable, you direct more of the potential black market to a legal market of such firearms.
This means the most effective way to disarm people of effective arms is not to ban guns, but to ban some kinds, greatly restrict others, and channel those that pursue firearm ownership towards that which poses least risk of resistance to government.
Channeling the market, minimizing the random black market by channeling a legal market that restrictions can be placed on, insuring more people participate in legal avenues to acquire that which is not feared by government rather than randomly acquire what is available on a black market.
Since governments fear shotguns least of all, it would be counterproductive to this strategy to over restrict shotguns in general, or shotgun ammo.
On the contrary governments would rather every civilian gun owner be using shotguns and their troops be as impervious to rounds from the peasants as the North Hollywood bank robbers were.
