After thinking about it, the gas used to cycle the bcg vents out the side, but most of the energy was transferred to the bcg.
The forward energy of the bcg was transferred to the shooter during the forward stroke as I mentioned above. The net recoil is the same.
Another example, hit the bolt release on a locked back rifle. The gun recoil, then gets pulled forward upon slamming home resulting in zero net recoil.
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