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Both guns rely on weight, muzzle brake, and a traveling barrel assembly. Plus the XM109 uses a 25x59mm grenade, not a 25mm cannon round (.50 BMG is 12.7x99mm). The muzzle velocity on the XM109 is about half that of the M107. All things considered, I’d be surprised if the XM109 had a significantly higher felt recoil than the M107.
Also, the two use the same lower receiver. That’s why the magazine pictured is so much shorter than the mag well of the rifle… The difference between 25x59mm and 12.7x99mm.
Here is a picture of an M107 packed for transport in its case, showing the upper and lower separate, so you have an idea of what parts are what. http://www.imgur.com/jHHzS8Y.jpeg
Edit: more comparisons… Here are [25x137mm cannon shells](http://upload.wikimedia.org/wikipedia/commons/5/52/US_Navy_090129-N-4774B-008_Gunner%27s_Mate_2nd_Class_Nicholas_Brassard_inspects_rounds_for_the_MK-38_25mm_machine_gun_system.jpg) for the [Mk38 naval autocannon](http://en.wikipedia.org/wiki/M242_Bushmaster#Naval), which is the ship-based version of the M242 Bushmaster that is on the Bradley. If that was what the XM109 shot, then you would probably be in a world of hurt after firing it.