You really don't want a drop in bobbin on a frame. This is why all long arms are vertical bobbin systems. Drop ins are harder to get to than a vertical bobbin (think of a quilt on top of the machine on a frame). And many will tell you the tension will be easier to get right on the 15 type bobbin assembly. I have a 301 set up on mine currently and when it warms up I plan on putting my 15 on it.