Well, this is an interesting coincidence, posting an example of my work just before I got around to replying myself, because those lower two images are of my -then small- collection, circa late 2018.
First off, let me introduce myself - I am the guy who, back in 2015, made a
series of illustrations for a book called
"Regiunea Întărită Focșani-Nămoloasa-Galați" (The Fortified Region Focșani-Nămoloasa-Galați") Published by the Romanian Military Museum, detailing, amid other things,
the turrets,
guns and ammunition of the FNG front, including the
53mm Gruson guns.
Unfortunately, in a tragic twist of fate, one of the main authors of this book, Ioan Scafeș, passed away suddenly in the morning of January 1, 2021. He would have loved to see this discussion and the new data resulting from it, but sadly, he won't be here to enjoy it. He will, however, be missed by us all.
But back to the main topic of discussion. I can certify that yes, the shell you posted in the last answer is indeed a Romanian 53mm Gruson model 1887 common or segmented cast-iron shell equipped with the Model 1888 (also known as Md.1887 modified) percussion fuze.
Interestingly, when first adopted for use in fortification Fahrpanzer and disappearing turrets, the Gruson 53mm would have used only the Md.1887 common shell and the case shot, with no other ammunition available.
In the 2015 drawing I did for the book as well as the pictures from 2018 the case shot is painted red, because of a note from 1890 which suggested this be done to make it easier for crew to tell the common shell and the case shot apart in the gloom of the turrets, but further documents which came to light since then suggest this was never actually done and the case shot remained natural metal.
As for
FZG76's mystery shell, I agree with both
MINENAZ16 and my friend
Irod7 that it's most likely a French produced shell for use in the Romanian 53mm Gruson. The fact it has a separate ogive and a different driving band I chalk to differences in manufacturing techniques, especially since this one looks to be made out of machined steel, not cast iron. Not sure about the fuze though, since I haven't seen any of that type before. It puts me in mind of a 25/38 Budin from a 80 or 90mm DeBange, but that's definitely not it...
In case you want to see what almost the "whole set" of Romanian produced ammunition for the 53mm Gruson would have looked like, according to a manual from 1930, here are a few from my collection.
Four of the cases are original and I included their markings for reference, the rest and the projectiles are 3d printed from plans and measurements of original examples, because not only am I a model maker by hobby, I also refuse to refurbish ground dug examples, because I'd rather not repaint a rusted an pitted projectile - and let me tell you, almost all of the examples found in Romania are incredibly rusted and most are live, so they get handed off to EOD for disposal.
So we have:
A) Model 1887 common cast iron shell. Black powder filling, Model 1887 percussion fuze. Painted black.
B) Model 1887 segmented shell. Black powder filling, Model 1888 (Md.1887 modified) percussion fuse - same internals but changed profile to make it easier to manipulate. Also painted black - by 1930, the bourellets of both these shells would have been natural metal, but I preferred to show the version used during WW1.
C) Model 1915 high-explosive shell, fitted with the Model 1904 percussion fuze from the Krupp 75mm Model 1904 field gun. In order to fit this fuze, the ogive was cut down by 8mm. Painted yellow, with natural steel bourrelet. Inscription as follows - M.T. ("Melinita Tasată", "Tamped Melinite) 53/87 (calibre and model). The casing is inscribed "170gr PFF ("Pulbere Fară Fum", "Smoke-Less Powder") Lot.1 29/927 (Lot.1, Arsenal receipt number 29, year 1927)
Some Md.1887 common and segmented shells were also cut down and fitted with the Md.1904 fuze. Since they would have retainded their black powder filings they would have been black and unmarked, but otherwise looked identical to the HE shell.
D) Model 1915 HE shell fitted with the French 24/31 Mle.99/08 percussion fuze. Only the black capped, 0,05s delay fuze was used. Normally this shell was delivered with a transport cap made from a cut down fuze, and the black part of the shell would have been inscribed in yellow ink "Gently take off the plug and put in a French fuze". Since I haven't found a picture or drawing of the original inscription, the shell remains unmarked. The ogive would have been inscribed in black "M.Ta. ; P.A.B" ("Melinita Topită cu amorsa", "Cast Melinite with booster"; "Pyrotechnia Armatei Bucuresti" "Army Pyrotechnic [facility] Bucharest"). The ogive is described as slighly rounder than the model 1887 shell and the filling would have been 110 grams of melinite.
E) Same as the one before it, but this shell is made out of cast steel and coloured brown. Markings in black would have been "M.Ta. ; 53/87 ; F.O. ("Fontă Otelită" - "Cast steel")
F) Model 1887/913 Shrapnel, pictured here with the Krupp 15-second time-and-percussion fuze, in effect a smaller version of the fuze present on the 75mm Shrapnel of the Krupp Md.1904 field gun. It could have also mounted a simple Model 1887/913 10-second time fuze or the 24-second "Burileanu" double effect fuze, which was also used for anti-aircraft work in the 53mm guns fitted on high-angle mounts.
G) Model 1887 case shot, tinned sheet steel, lead-antimony bullets with sawdust packing.
Finally, here are two plans from the 1890 manual depicting dimensions for the common shell and the case shot:
Also,
MINENAZ16, are you willing to give me accurate measurements of your French made shell? I'd love to add a replica of it to my collection...