BMG "FA 40" question


What caused these spiral grooves on the headstamp?


[quote=“sksvlad”]What caused these spiral grooves on the headstamp?

Sloppy machining. The head of the cartridge has been faced off in a lathe and the spiral is the tool being retracted after the facing operation. It simply scraped across the machined surface.



Even though these were made early and were peace time production for the USA, the quality is terrible. Why did this happen when the factories were not under the stress or wartime production?


BY 1940, the US procurement Plans started in the late 1930s were already in full swing. The head turning used in preparing .50 cal is automatic, like rim and groove turning in smaller cartridges, only that the smaller cartridges don’t need the face of the Head to be turned…for some reason, the Bunting/head forming operation in larger cases requires “Facing off” to give a level, flat surface.

The automatic Lathe tool is simply either worn, chipped or badly set to start with. ( new staff, untrained staff, “Monday-itis”)

Doc AV
AV Ballistics.


Falcon, my friend. What other features of these cartridges causes you to say the quality is terrible? Is it only this groove? I don’t know if this groove would cause them to be rejected - if so, you would think the cases would never have been loaded. However, such marks are inconsequential, in my opinion, to the function of the cartridges.

Since the whole cartridges are not shown, perhaps there are other anomolies that indicate poor quality manufacture?

John Moss


The cartridges look normal to my non-professional eye. Someone pulled the tracer bullets and emptied gun powder. Is there a way to re-insert the projectiles fully?


They look bad from the mark from the turning tool being removed, the off centre primer crimps and the bunter on the last one looks to have about half of it chipped off. I suppose if they were already gearing up for war at this time and trying to produce as much ammunition as possible then this was probably ignored.


I’m not a collector of 50 BMG but I have some and I checked them.
I have an SL 42 fired case showing the rings quite clearly while an unfired SL 4 has them but they are very faint and difficult to see with the naked eye. An unfired LC 85 Blank has the rings AND the larger, deeper hook-like mark present in the photo.

Interesting subject but I just never would have considered these marks until now. As for quality, I think of stories I’ve read about French made ammo in WWI that was bent and would jam weapons! That’s poor quality to me, not cosmetic marks, but perhaps thats why I don’t collect the big stuff.