Blank for 75mm Mle. 1897 Cannon?

I have a French 75x350R case that has been cut down to a 206mm length. I believe this case was converted to a blank rather that just cut down, as the flea market trader I got it from had two of these cases, both equal length with identical headstamps. Both cases also had the remains of lacquer and paper at the same height on the inside of the neck where the charge would have been held in. Both cases also appear to have been chemically treated as they have a distinctive dull yellow colour.

The headstamp is: “.75 - 1897 - G Sc - Bx.5.7 - 39 -” along with inspectors’ marks of “B” in a circle (stamped in 2 separate places) and the flaming grenade symbol.

The case has some modern looking stampings in black ink on the head. These are:
“4. Br. 74-S” in a straight line on the top half of the case head above theprimer, and “0,750 Kg PN 4” in a straight line on the bpottom half of the case head below the primer.

The primer is a two-pin screw in type, and is marked: “SFM 49 47 A [triangle in circle] [flaming grenade]-25.47”

Any info on the purpose of this case and the meaning of the markings would be helpful.

Any ideas?