That is the cleanest breaktop I've ever seen!
It's a Third Model given the use of the coil main spring instead of a leaf spring.
I don't know for certain when Iver Johnson switched to the coil main spring, but I THINK it was after World War I.
OK, just found some information that says that the Third Model came out in 1909 and went until 1941, so your gun is sometime between then, apparently.
You'll also notice a very neat feature...
Those serrations in the frame that hold the mainspring plate allow you to adjust the mainspring tension.
Pretty nifty design.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.