the easing function `swing` is really `easeOutQuad` in jQuery easing lib compared to plain jQuery

swing-easing.md

http://gsgd.co.uk/sandbox/jquery/easing/jquery.easing.1.3.js https://github.com/gdsmith/jquery.easing/blob/master/jquery.easing.js#L21

Relevant parts

// Preserve the original jQuery "swing" easing as "jswing"
$.easing['jswing'] = $.easing['swing'];

$.extend( $.easing,
{
	def: 'easeOutQuad',
	swing: function (x) {
		return $.easing[$.easing.def](x);
	},
...
easeOutQuad: function (x, t, b, c, d) {
	return -c *(t/=d)*(t-2) + b;
}