Yes.

Most current OS engines recommend minimum 18 percent oil; castor, synthetic, or blend.

In many cases, modern two stroke and four stroke fuels are identical except for the label. There are still some 'four stroke' fuels with low oil content but it is not as common as it used to be.

Contact S&W http://www.splube.com/contactinfo.html and they'll tell you what's in your current fuel. There's a good chance it is fine for an AX.