...it's weird that it's made of steel though, no? During war, (WW1 and 2 anyway) steel alloy was at a premium. The British have been using brass on butt plates going back to at least the Brown Bess, maybe even earlier, I dunno?
I know the (American) Savage LL #4Mk1's had aluminium butt plates due to war time expediency and material allocations...steel is like war time gold...to screw it to a rifle butt stock doesn't make much sense to me, but there it is none the less!?
Some additional information for you.
Ferrous iron ore (hematite) is one of the most abundant rock elements, constituting about 5% of the Earth’s crust and is the 4th most common element in the world. It is not really wartime gold, it is the most commonly used material in war because it's literally everywhere. Steel alloy is a different matter, some of the alloying elements of high grade alloys are rare, but that buttplate is likely forged from 1018 low carbon steel and AT BEST it was surface hardened with carbon.
Brass, on the other hand, is primarily made of Copper and Tin. BOTH of these materials were highly valued in wartime production. Tin is the expensive part of solder and copper is used extensively for wire, bullet jackets, shell casings, etc.
Aluminum, in WW2, was also at a premium. WW2 Enfield buttplates are made of Zamac, an alloy primarily made of zinc. The original alloy was invented by the germans and the exact composition includes Zink (zinc), Aluminium, Magnesium and Kupfer (copper).
Typical percentages of non-zinc elements:
Aluminum: 3.9-4.3%
Copper: 2.6-2.9%
Magnesium: 0.025-0.05%
The rest was inexpensive zinc that would be too soft without the alloying trace elements.
Here in Canada, we used forged steel buttplates on the Lee Enfield because we were not being bombed and didn;t need to resort to cheap castings made in de-centralized small workshops like the brits did.