Cannot speak of the 870 but I know for a fact that a forend made to fit an 11-87 with a LC barrel will not fit onto a slug barrel. A buddy recently picked a slug barrel for his 11-87 and his original forend did not fit. Thankfully, I found a standard synthetic forend for him on the EE and it works fine. Remington does not make LC slug barrels, just standard ones. Again, I'm talking about an 11-87 not an 870 but I wouldn't be surprised if the same applies to it. I'm sure there are people out there who sand and/or Dremel the LC forend to fit but making it slightly oversized does not help with the fit once placed on the field LC barrel again.