Actually I own a XM8 that was converted from a SL8. The barrel on mine is short but still has the heavy SL8 profile. I would say the recoil between it and my Colt M4 carbine with a 16 inch barrel is comparable. I dont note a difference in felt recoil. The XM8 is more front end heavy than the M4. Ditto for the G-36, I have a couple Tommy Built T36 clones of the 36, both E and C models.
https://imgpile.com/i/umJ5G4