Looks like it's a carbine version of this rifle...
5,000 of the Remington M1867 rifles were made into the carbine version, which is the type of rifle my friend has. You can read all about this rifle at... http://en.wikipedia.org/wiki/Remington_M1867
The caliber could be either 1 (8x58R Danish) or 3 (12.17x42R) in this pic...
1- 8x58R Danish
2- .30 Gov't (.30-40 Krag)
3- 12.17x42R Norwegian rim fire
4- .45-70 Gov't