Originally Posted by DWalt

It looks correct. It is highly unusual to see one of them and you are very fortunate to have found one. I believe all of the FBI M81 rifles were chambered in .30 Rem. At least for a while, the FBI used a special more lightly loaded version of the .30 Rem cartridge, and the FBI version of the M81 rifle used the lighter recoil spring of the .25 Rem rifle. Originally, the FBI M81s had a fitted leather case, but I have never seen one of those. .30 Rem ammo is somewhat difficult to find today, but it is occasionally seen at gun shows, often the "white box" FMJ loads made for law enforcement and prison use by Remington back in the 1950s-60s. You can use .30-30 dies to reload for it. Not exactly correct, but they will work. You can also convert .30-30 brass to .30 Rem if you have access to a lathe. I have made several hundred .30 Rem cases that way. At one time, it was not too difficult to find new .30 Rem brass as Remington continued to sell a run of brass every so often. But I don't think they have made any for the last several years.