Thanks to Caylen and WiseWolfHolo for helping me by sitting around and shooting me a lot.
The only way sniper damage can be clocked is if we create a condition wherein a person can absorb damages exceeding 100. I had previously attempted wallbanging to proportionally decrease damage, or amount of damage inflicted on infection hosts. However, I decided to stick with solid numbers and no guesswork.
First thing to establish: friendly fire penalty. I had estimated the FF penalty to be around 32%. I had conducted tests which indicated that the Beretta deals 32 to 36 damage with an average of 34. Damage tests on friendlies indicated an average damage of ~10, which equates to a damage reduction to 30% of original damage. Using the 30% figure, I found FRF2's damage on a friendly and multiplied that by 10/3.
Reversing the assumed 30% penalty, the FRF2 (modded with LRB) dealt an average of 123 damage and a median of 122 damage for an approximately normal distribution with slight skew to the left and outliers on the right. It dealt anywhere from 105 to 150 damage, although the main grouping was around 105 to 130 with a flier at 138 and 150.
Keep in mind that the body part multipliers are 1.5x for guts, 1.25x for chest, 1x for arms, and .7x for legs. An average of 123 damage indicates that a legshot will almost always tag (this is true - try it yourself!)
It should also be noted that the FRF2 has the best armor penetration in the game for unknown reasons. It practically ignores EA08 and SA09 and rarely has more than 3% damage absorbed against anti-sniper armor.
I hope you get a good idea of how sniper rifle damages work. Also keep in mind that clocking sniper rifle damages is a work-in-progress and I'm seeing how other guns interact with a friendly fire multiplier (and whether the FF multiplier is really 30% or something else like 33%). Don't take the figures I listed as fact; rather, they should be used as a rough estimate as to how far above the scale sniper rifles really hit.