7x57mm Mauser AP?

I was shooting my FN-49 today which is in 7x57 Mauser at a target 300 meters away. The target is a 100 pound AR-500 gong.
I was the last to shoot at the target. The spotter told me he could see the hits clearly on the plate. The bullet jacket is cupro nickle and we thought that was the cause. On my 5th hit on the plate the spotter reported a very bright red flash on the target. I secured the rifle and we drove down the the target.
My rounds had struck the target at a 20 degree angle due to the target stand and firing position. Two of the bullet had almost gone through the 1/2" AR-500 plate. You could clearly see the conical shape of the perpetrator.

My question is, what were those rounds?
The marking on the head stamp is:
“HP” at 12 o’clock
1927 at 6 o’clock. The numbers are European semi-script.
The is NO color ring around the primer. The primer is silver metal.
The is no paint on the bullet nose or around the crimp.
There are no other marking on the case.
One round had a dud primer. I should be able to pull it apart and provide photo’s and what it is loaded with.
Any ideas?
The case is brass.

Looks much like the time I shot at AR plate with .30-06 M-2 AP. Thought it was mild steel, but after resisting the AP hits it was determined to be AR plate.

You have a dud example of this ammunition, so it should not be difficult to determine the construction of the projectile with a little judicial sanding, cutting or filing.


This earlier thread discusses a cartridge with a similar description:

iaaforum.org/forum3/viewtopi … 6&p=101101

IAA Journal Issue 489, Jan./Feb. 2013 on page 47.