Damaged frame

[mrerick]

Wolfe GunSprings makes a kit with a number of different weight Luger recoil springs.

https://www.gunsprings.com/

It would be worth trying the masking tape test (put masking tape in the area where the rear of the toggle train impacts the rear of the outside of the frame, just above the lanyard ring area) to see how hard the action is slapping the frame during recoil. Look for how heavily the masking tape gets marked and compressed.

The FAQ document (available through the link at the top of every forum page) had a table of spring weights in terms of number of turns and gauge of coil steel. There were a range of strengths used over the life of Luger manufacturing as well as differences between springs used for the .30 Luger and 9mm Luger rounds.

Never use a 9mm load marked "NATO". This is higher than normal. My preference is 115gn standard velocity and available from a number of manufacturers. Winchester likely uses their 231 pistol powder (HP-38) so similar burn characteristics are desirable.