Help identifying a 1945 brass shell casing - General Ammunition

Hi, My son is a huge fan of tanks and we found a 1945 shell casing and I was hoping you guys might be able to help me find out some information about it for him. Such as who was the manufacturer, what sort of gun would shoot it. Sorry my google searches are not coming up with much. The markings on it are: 25PR Lot 403 1945 RLB I will try and post a picture Thanks in advance, Cheers Amy

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