Typically speaking, Milky Way shots (assuming you're not using a tracking mount) are very close to all the threes - ISO 3200, f/2.8, and 30 second exposure. ***
IMO, you're not going to be able to get anywhere close to that exposure even with a 260 and pull off a decent shot.
If you've got a tracking mount, then perhaps you could do something, but even then you have to recognise that most of the deep sky astro shots you see will be stacked from multiple (often dozens) of shots.
Usually with a focal length (35mm DSLR) in the 14-20 range. Any longer than that, and the necessary shutter speed will produce star trails.