6601 is the 20" right? If the rifle wasn't having problems why did you change the extractor spring insert? Or, did you change the extractor sping [b]and[/b] its insert?
There is no difference, except color, between the blue inserts and the black inserts. The [b]military[/b] uses the colors to denote different spring weights. The [b]military[/b] considers the insert and spring to be one piece. Manufacturers and dealers are another matter. Companies often buy inserts and springs separately and assemble them at the company. It's easy to get a crappy spring with the [i]correct[/i] insert in it. Either weight spring will work in rifles.
Yes, you can put the spring in wrong, if you put it in upside down (small end down) you can cause the spring to compress and STAY compressed. If you do not snap the large end of the spring into the extractor you can cause excess tension on the extractor which can cause FTF.
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