There's much more to the extractor then just proper tension.
As for the amount of tension 16 to 20 ounces is plenty on a 45acp.
Some will say with the slide off the gun and the barrel removed, place a loaded round against the breech face of the slide, if the extractor holds it in place you have the proper tension, I don't buy this as the extractor may be to tight.
You also need to make sure the extractor is not clocking, if it is, it can definitely cause failure to feed and failure to eject problems.
If you are unsure of how to fix or check these problems it may be best to consult with a smith in person about what your gun is doing.
If the extractor in your gun is loosing it's tension I recommend it be replaced with a good quality 4330 or 4340 extractor, that will cure the problem.
Best Regards
Bob Hunter
www.huntercustoms.com