OK, before we go swapping parts and grinding on the slide, lets do an inventory.
1) With the slide off the frame, slide an empty case up under the extractor. Does the case hold to the breechface? If it won't hold, or just barely holds in place, the extractor might need to be tightened up.
2) Again with the slide off the frame, slide that case up and down the breech face. While doing it, have a look at the extractor's rear portion, where it ends at the back of the slide. Does it rotate noticably as the case slides up? If so, you may benefit from a new tighter firing pin stop. This condition is know as clocking, and it means that the extractor hook is not held in a fixed position. The result can be a wide varience in ejection pattern.
3) Is your 1911 ancient, or relatively new? Most made since the 1980's have an ejection port that is fairly wide open. The origional guns had a fairly small ejection port that worked fine with full power FMJ ammo, but would puke on lighter handloads.
4) What ammo are you using? If it's lighter reloads, or if you are giving the gun less than a firm grip, the ejection can be less forceful. In some cases, a lighter spring can help.