Feeding Issue

[heysox]

I took a friend shooting so she could try out her late Granddad's bring home Luger. It's an early (1913) Erfurt. The magazine seems period correct but has a different serial number, which is not unusual for military firearms. (I'm certainly no expert). I'm a Luger noobie, but experienced shooter/enthusiast for many decades. The magazine was loaded and has probably been so for decades, as the rounds were tarnished. The Luger (I had previously stripped and cleaned it) fired off the entire mag with no issues. I reloaded it with a mag of Aguila 115 gr. ammo. It would not feed at all. The top round nose dived below the feed ramp. I tried a single round in the mag and that fed just fine into the chamber. I loaded the mag fully and the Luger went through all the rounds with no nose diving or issues. Past experience has taught me that many if not most feeding issues are magazine related. I suggested new magazine springs. She only has the one magazine, so I could not positively say it's a magazine issue, but it seems very likely. Internet research indicates that there are square and non-square mag springs. Any way of knowing that without taking the mag apart? I don't have access to it and wanted to get her the springs as a surprise. Any thoughts from the Luger brain trust? What is the best source for new mag springs? I am sure that there is more than one modern maker. I will check Youtube for videos on swapping out the springs. TIA.