Usually, the question "is it legal" means is it a firearm not subject to the NFA of 1934, i. e., may it generally be purchased in accordance with only the formalities required under state law by someone generally qualified under state law to own a firearm. And the answer to that questions is "no."
This is an NFA weapon and requires qualification under federal law, registration under the NFA and the payment of an NFA transfer tax. It may also be illegal under the laws of some states that further restrict NFA weapons.