Grams STI mag springs in G35?

[OUshooter]

Well I ordered Grams mag springs for my G35 Limited setup. I should have known something was odd when there wasn't a place to pick the type of gun the mag was used in.

Anyway.... The package insert says the spring is for an STI/SVI mag up to 145mm. I'm having feeding issues because after the first 2-3 rds come off the rest of rounds bind up, i.e. you can take the mag out and here loose rounds rattling around.

So is this because I need some tuning or because the spring isn't compatible with the mag?