I'd be interested to know Iowa 303 - what is the year of manufacture of your MSch M1903?
Here's a direct comparison: Your mag. & my mag.

Iowa 303 M1903 rotary magazine... a clearly smooth flowing lift ramp

This is my M1903 rotary magazine... a not so smoothly machined lift ramp

I'm guessing here's where I need to sort the problem out - the lift ramp.
Waidmannshiel I'd be interested to see a photo of your M1903 lift ramp...can you do please?
Cheers, deeangeo