Impossible to say for sure, - Amberg and all the Berlin firms used a stylized "F" or "J" during the war, extensively in ranges, persoanlly I interprets Amberg's letter as a "J" and the Berlin firms as a "F", this is especially easy to confirm due to the fact DWM eventually goes to a Latin or Roman "F" which is indisputable.
This is all in ranges and changes at times, but my guess would this is more akin to an early Berlin style rather than an Amberg style, though I could not find an exact match in a quick search.
To add to this identification problem is the fact that all the firms "shared" components, typically the arsenals doing huge numbers of a specific component and that part sold/delivered to other makers, so it is often the case that small parts can't be tracked accurately. This is especially true of TG's. I generally do not trend these small parts because of this erratic nature of acceptance (something I do trend on 1934-1945)
Anyway, the letter has much in common with Amberg, early DWM and somewhat with Spandau, - WOK is highly stylized usually, but I do not have time to examine many rifles in the database. I will say the style of the F/J does change slightly over time and often part to part, so you would have to take a broad look to any sample (this doesn't even consider pre-war where erratic is given a whole new meaning... wild inconsistencies with large numbers of inspectors... trending small components on pre-war is a wasted effort imo, I only trend stocks, receivers and bolts acceptance, especially at the arsenals, - Mauser, DWM and Amberg for obvious reasons are exceptions, their rather independent/isolated nature gives them some consistency, - the damn Prussian arsenals are wildly unpredictable, worse than a woman...)
