Consigning luggage Beijing to Xian

You actually do not need to consign your luggage, as the weight limitation is not as strict as on planes. you can carry your luggage on board.

Two large suitcases weighing more than 20 kg
Thank you Polly for your reply. Unfortunately, I did not make it clear that we will have two suitcases each - weighing approx 25 kg each. Therefore 50 kg per person. I believe we may not be allowed to carry that much on a G Bullet train? Can you advise please.

actually, no one will stop you from taking your luggage onboard as long as you can.
your suitcases are too large for the luggage rack, but you can put them in the large luggage closets between two carriages. so you' d better get onboard early.
i don't not suggest consign your luggage because that there is no luggage carriage on the train you take, so you need to consign your suitcases one day ahead of your departure at Railway station. the luggage will arrive at Xian Railway Station, but you arrive at Xian North Railway Station.