To clarify a bit, the 1903 and 1903-A3 barrel are both the same length (24.0") and are essentially interchangeable aside from the front and rear sights. However the 1903 barrel is slightly smaller for the first few inches in front of the shoulder, where the rear sight collar would normally fit over it. The 1903 barrel also has a bit of "choked" shape in this area while the 1903-A3 barrel has a straight taper.
Out of curiosity I measured a sample of three different 1903 and three 1903-A3 barrels with vernier calipers and came up with the following average diameters:
0" in front of shoulder: (1903) 1.14" / (1903-A3) 1.18"
1" in front of shoulder: (1903) 1.14" / (1903-A3) 1.16"
2" in front of shoulder: (1903) 0.99" / (1903-A3) 1.02"
3" in front of shoulder: (1903) 0.96" / (1903-A3) 0.98"
4" in front of shoulder: (1903) 0.91" / (1903-A3) 0.94"
5" in front of shoulder: (1903) 0.88" / (1903-A3) 0.90"
6" in front of shoulder: (1903) 0.85" / (1903-A3) 0.86"
Of course this was not a very scientific survey, but I think it illustrates the difference pretty well.
Last edited by Peconga; 01-22-2014 at 12:33.
Cheers,
Peconga in Boise, Idaho