Bernina Express May 15 from Chur to Davos
 

We wish to take a round trip Bernina Express trip from Chur to Davos. I saw the option somewhere that said it only goes in the summer. When and where can I buy tickets, please? We are driving to Austria afterwards but can't pass up the train ride.

Regular trains go all the time Chur to Davos and sometimes the Bernina Express serves that route on its trip up to the summit of the Bernina Pass - Chur to Davos is nice but not nearly as dramatic and the Bernina Pass trains - maybe you mean leave Chur and do the Bernina X and take it back to Davos - well just take regular trains or the BEX if running from Chur to Bernina Ospiz - a summit station and back to Chur and regular trains to Davos.

Anyway you can book BEX trains at official site: https://www.rhb.ch/en/panoramic-trains/bernina-express

No need to book Churto Davos - those are regular trains just buy at station if BEX site won't allow that.

For lots on Swiss trains and booking BEX www.seat61.com; BETS-European Rail Experts and www.ricksteves.com.

The Chur - Filisur - Samedan - Alp Grum - Poschiavo - Tirano Bernina Express train runs all the year round.
The Tirano - Poschiavo - Alp Grum - Samedan - Filisur - Davos Platz Bernina Express train runs from May 11th until Oct 27th

It would be easier to go directly from Samedan to Austria:
Samedan dp 8.13, 10.13, 12.13, 14.13, 16.13; Innsbruck ar 3 hrs 50 min later, Salzburg ar 5 hrs 50 min later.

No reason to go all the way to Tirano - rather get off at summit stations Alp Grum or Bernina Ospizo (can do easy walk between them) and back.

if you want to go to Davos don't bother with the Bernina Express. Aside from the Landwasser Viaduct the sector Chur/Filisur/Davos is not specially scenic. And in fact you will most likely be on normal trains for at least the Chur/Filisur part of the route anyway. If you want to take the Bernina Express then take it to Tirano and take a local train or trains back to Chur - with perhaps a stop over or two en route. Poschiavo and St Moritz or Pontresina would be nice. If you want a smaller Engadin village then stop in Bever.

The Rhätsichebahn that runs these trains is gradually introducing new rolling stock so you do have a chance of getting a train with panoramic windows on the "normal" trains. These new carriages also have a commentary. Limited by comparison to the Bernina Express but nonetheless informative. However you cannot be sure what configuration your train will have...maybe on a local train "old" rolling stock or maybe "new".

Local trains so nice because no reservations so just hop and off - BEX book far in advance though seats could be available right up to train too but usually not I believe.

Depends on the time of year for the BEX... July and August and most of September it gets really full. But often getting just one seat is possible right up to the last minute. It is when 2 or more want to sit together that it gets very difficult... As you say, PalenQ - local trains are not a problem!

The OP will travel in May (something like Chur - Bernina - Davos - "Austria").
If it would have been in summer, I would have suggested the circular day trip Chur - Albula - Bernina - Stelvio - Umbrail - Fuorn - Vereina - Davos.