There is an enigma about Frank Hamer's Model 8. He had one but it seems to have been chambered for the .25 Remington. No one knows for sure. Almost certainly, he used a Remington Model 11 shotgun during the B&C ambush, not a Model 8. The rifle most commonly associated with him is a Model 81 in .35 Remington, which he owned, but the Model 81 did not yet exist at the time of the ambush.
There is very little difference between the Model 8 and the Model 81, aside from the stock and fore end design. Probably the most common chambering for the Model 81 was the .300 Savage (for which the Model 8 was never chambered).