Failure to extract problems, etc.

Hi all,

I am new to the forum, and I am pretty much a novice with firearms. I bought a new synthetic stocked, stainless Mini-14 a little over a year ago. From the first time I used it, I've had failure to extract issues. At first, being a new guy, I thought maybe I wasn't loading the mags properly, or the gun wasn't broken in yet. On my first trip to the range with 100 rounds of Winchester USA ammo, it failed to extract about 1 in 4 rounds, and I gave up after 30 rounds fired. I cleaned it thoroughly tried it again a few months later. This time I went to the range with Wolf steel-cased ammo and Winchester USA ammo. I had no problems at all with the Wolf ammo, but when I tried the Winchester ammo it FTE'ed within 5 rounds. I went home disappointed and cleaned it again. My third trip to the range, I went armed with a third kind of ammo, Federal American Eagle. Once again the Wolf functioned flawlessly, but the Winchester had problems. Also, the Federal ammo failed to extract within 3 rounds fired. So now, my conclusion is that it can only handle steel cased ammo, but there must be something wrong with the rifle since it won't extract brass cases reliably. I'd like to try to fix it myself if possible, but if that isn't feasible, I'll just send it back to Ruger for repair. But, I have a feeling, it may be something simple. From what I've read it could be the extractor plunger or the extractor spring. However, I don't know how to disassemble the extractor, plunger and spring. Any advice? Am I on the right path?

On another note, I got overzealous with my cleaning the last time, and disassebled the gas block. After doing so, I saw in Ruger manual that is a no-no. OOPS! It says that they torque screws to some spec at the factory. Do I need to be worried about this?

Lastly, I heard some say that the steel-case ammo is harder on guns than brass-cases ammo. Is there any truth this idea, or just a legend?

Sorry to ramble on so long. I'd appreciate any help.