Kent's rank is given as Private while after he is exhumed his Class A uniform has the rank of Corporal.
Brennan picks up Jimmy's cigarette the first time she and Booth question him, ostensibly to use the residual cells for DNA testing. However, as military personnel, Jimmy's DNA would already be on file in the military's DNA database.
Retrofitted M14 rifles were used during the Operation Enduring Freedom, but they were redesignated as the "Mk.14 EBR", and only handed out to Special Forces units. The M14 seen in the episode is a civilian M1A rifle in a Sage chassis kit, possibly intended as a mockup of the aforementioned Mk.14. During Operation Enduring Freedom the urban weapon of choice was a M16A4 5.56mm.
When Dr Brennan and Booth are looking at the ranger's headstone and Zack is in the background near the burned body, one of the headstones between them is swaying in the breeze.
When Brennan and Booth are watching Kent's coffin being raised from the ground it's visible that, between the coffin, two of the tombstones on each side have the same name. Both saying "Fred Johnson, OCT 6 1986 - JAN 19 2005" One is located on the left side by the excavator and the other on the right side, right next to the red spotlight.
After the bullets are removed from the body of the dead soldier, Booth immediately deduces that 3 of the rounds were fired from an M-14 instead of an AK-47. Both the M-14 and the AK-47 fire a 7.62mm bullet and while the cartridges are different in length, the actual bullets are practically the same size. It wouldn't be possible to determine what rifle they came from at a mere glance. Also, there are many different rifles that use the 7.62x51mm (.308 cal) round besides the M-14.