Extraction problem

[brokenknife]

I have one of the early stainless steel Aimco lugers. It has a problem with extracting the spent shell. When fired, the shell stays in the chamber causing an interesting jam. The problem occurs with almost every shot fired. I have cleaned the chamber very well and have not noticed any roughness in the chamber. I can cycle (by hand) loaded ammo from the mag, to the chamber, and extract without any problems. Has anyone else had this kind of extraction problem? The extractor spring seems to be a little weak. I can move it with my finger quite easily (pushing down on the extractor furthest from the hook) with about the same pressure it takes to pull the trigger. Is this normal? Any other ideas? I have recently taken the extractor out and filed a little in the center to get a more complete grip on the casing. I have not shot the pistol since making this modification. The chamber does seem to be a little generous in size-could this cause any problems? Oh, I was shooting factory Remington UMC 115 gr 9mm. On the upside, it does load from the magazine well. Sorry for the long first post. I really like this pistol and would like to find its full potential (being able to shoot a full mag without having a major jam). Thanks