Remington as did most manufactures used many different size barrels Some of them were wider than the receiver. They would accommodate what the customer wanted. Here are the measurements at the breach of the six Hepburns I have access to. 1.00", 1.02", 1.03", 1.18", 1.19", and 1.23".

Cheers,
Laurie

According to Tom Rowe's book "Reminton's N0. 3 Hepburn" Winchester's barrel system has become a de facto standard for identifying barrel sizes. He states that the most common sizes are no.3 (1 inch) and no.4 (1 3/32). He goes on to say that no. 5 barrels are slightly larger than the action,no.6 projects about .25 and no. 7 and 8 are monsters and very rare.
Rowe's book is $125 and worth every penny just for the pictures!  Dennis