Hello all, firstly G43's are not my main forte, however I am mainly a French military collector.
Here is my humble opinion of the "mystery."
I believe the circle "V" is actually of French origin, and is used to indicate which forge provided the steel, and stamped/milled the part. The French had a system of letter codes to indicate which Forge provided the steel. (Examples with A,B,C,D,E,F,G depending on origin of steel and time period,... etc.)
In this particular case, a "V" would indicate the steel came from the "Forges de Firminy." They stamped their steel produced parts with a "V", especially those parts intended for routing to St. Etienne factory.
The forges made French tanks, in particular the St.-Chamond (total POS), during WW1. They also made field guns, MG's and steel for numerous small arms parts such as triggers, barrels, etc.
They started using the circle "V" stamp before WW1 and it can be found on Berthiers, Lebel 1886 M93's, and many other French rifles that used barrels from the Firminy forges. However they used the stamp all throughout WW2.
During WW2, the forge was still making steel, for the Germans. The factory produced steel parts for German rifles, including triggers, bolt locking lugs, Hotchkiss & MG42 barrels, and numerous other small parts, the majority of which it sent to St. Etienne to be assembled. The factories were not far apart, and they would actually merge post WW2.
This marking can be found on many small German used parts, and it is my belief that these G43 parts, triggers, lugs etc. all came from the Firminy forge, and were routed to St. Etienne where they were assembled on various receivers/rifles.
Notice the V is virtually identical to the ones pictured on the German rifle parts. Note that its a bit elongated, simply due to the fact this particular one is struck on a cylinder angle of the barrel. Once flat, its the same stamp.
In conclusion, I believe these parts to be made in France, at the Firminy forge, for St. Etienne.
Hopefully this can put the "mystery" to rest.
If you are interested in French rifles, stamps, markings etc., some excellent books are the following:
Le Fusil Lebel - Alain Barreller/Jean Huon
La Grande Aventure des fusils reglementaires Francais 1866-1936 - Henri Vuillemin
If you don't speak French:
Jean Huon's Proud Promise is a great read.
Here's a partial listing of some steel maker codes - this is a early printing, 1913 to be precise. Some changes occurred during ww1 later, and into ww2. But for the most part is good.