Let us go to basics: Without a year date, it is most likely a “commercial” or “Sporting” cartridge. TAP could be either an Importer in Pakistan, A goverment organisation (?T?A.Pakistan?) or even ( not likely) the cartridge maker in Brazil (if the source is correct.)
Being in the early 50s, it fits in with Pakistan’s recent formation in 1947 ( separation from India (British) at Independance.
7mm ( or “.275 Rigby”) was a well used Hunting Cartridge in the “old Raj” by both British and Local hunters alike, especially in Mountainous regions. Possibly teh new pakistan had a Game Department armed with Rigby/Mauser 7mm rifles???
THis is all assuming the “Brazilian Connection” is correct…