I would be careful to call it questionable...
@brianf It does not always necessarily need 3-piece cases for higher pressure.
@badassgunworks be careful too, do we know what the powder charge was or
do we know what powder it was? No
maybe lou got much slower powder from Vihtavuori. Maybe something experimental through good relations with the manufacturer or maybe not... who really knows....
So even if it is off topic, all the discussed stuff if and how you can accelerate bullet xy to 4000 fps was already tested a very very long time ago.
Frankford Arsenal and U.S. Military
did a lot of testing around 1940-1980.
Cartridges such as .50 HV, .50 US, .60 US and .60/.50. etc.
Guess what... even .50 cal projectiles at 3900+ fps is a real thing. Im not talking about 350 grain light weight bullets. Some old documents from Frankford arsenal and Franklin institut are over 600 pages long and I haven't finished reading all of them yet. I don't think all this R&D data is lying to me but anyway. I wouldn't consider 4000 fps with 415 grain bullets to be 100% unrealistic.
If anyone asks now why so many developments of HV cartridges never made it into service. One of the reasons
,when World War II and later the Cold War ended, there was no longer a need for such cartridges and throat erosion was a major issue with those cartridges.