I finally got my grubby paws on one of two known box styles of the developmental cartridges resulting in the M118 Long Range.
This box is a typical M852 “brown box” of the period with a paste on over-label with the USMC emblem. The cartridges are headstamped LC 95 LR making them the earliest LR headstamp that I’m aware of. The “S” in the lot number indicates they are a special lot not yet approved for the regular supply system. They are loaded with what appears to be WC 750 powder, to a velocity of 2700 fps.
The other box that I know of uses the same M852 box but without an over-label, and bears an LC-94 “S” lot number. The word “MARINE” is stamped below the lot number. This box is labeled as MATCH M852. Whether this box contains cartridges headstamped differently than mine, I’ve yet to determine.
If anyone has any information concerning either of these boxes (or any different ones) I would certainly like to hear from you.