sure, The biggest difference is barrel length, the FS is longer, meant for the infantry only, and can mount the C27 grenade launcher. Once the new ammo arrives it will allow a infantry soldier to engage targets effectively at 500m (there will be a PWT level 5 for 500m). Here is a side by side picture of CWO (Ret'd) John Yoshida showing them off the other night at 33 Svc Bn. As you can see the stock is a slightly different model as well to allow for a storage compartment for optic batteries. I am loving that we finally went with magpul for accessories, and PMags are coming too.
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