The 03A4 was the designated bolt action sniper rifle. The 03A3 was an improved version of the '03 used in WWI and intervening years until the Garand was adopted. You don't need to worry about 03A3's coming apart when fired as the bugs were ironed out of them long before these rifles were produced during WWII. The only ones that I'm aware of that have had improper heat treatment were the earlier 03's preoduced at the Rock Island arsenal with serial numbers below somewhere around 186,000.

The 03A3 had a receiver aperture sight, and several stamped metal parts and 2 groove rifling, while the 03 had its rear sight on the barrel, had 4 groove rifling, and used milled steel parts. These changes made the 03A3 a more accurate shooter and cheaper to produce. The army tested the 2 groove rifling extensively and found it to be no less accurate than 4 groove rifling.
The only real difference between an 03A4 and an 03A3 is the 03A4 has a scope mount and lacks a front sight.

Here's a sight with some more in depth history of the 03 series of rifles. http://164.109.174.105/publications/tar/general.asp

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