You can post with parcel force 48 hour.
You must use the 48 hour service as it goes by train and road.
And you can insure your item.
Wrap with a minimum of 5cm thick bubble wrap.
On another forum a claim was put in for a gouge in a custom stock they never paid out as wrapping was less than 5cm they said for breakable and fragile items thats the minimum it turns out in there eyes for rifles.