As others have posted, it's probably going to be against the uni's t&cs to keep rifs in halls of residence. The society should be able to advise you on alternatives.
I use a gun bag similar to this when using public transport to get to games.
https://www.patrolbase.co.uk/8fields-tactical-long-double-rifle-47-147cm-gun-case?pv=16035
When I first started I used to use a hard rifle case as it's more secure but I found it actually drew more attention from the public