Can I break my extractor

Not sure i understand the premise of the question. At 1.270 the 2 concerns i would have would be, 1) will it feed from the magazine, and 2) will the bullet be on the rifiling when chambered. I'd definitely test a dummy load before loading up too many at that length with a LRN bullet. As far as the seating depth having a negative impact on the extractor, I don't believe that would be a consideration. But LRN bullet profiles tend to have a wider radius at the nose compared to jacketed, and typically need to be seated shorter than a comparable jacked bullet to keep the bullet from hitting the lands when chambering. Having the bullet touching, or jammed into the lands can cause chamber pressure spikes...
Now, if the round passes the plunk test, and feeds from the magazine just fine...and is accurate from your gun, you probably have a winner.

BJung said:

Hello gunsmiths. Can I break my extractor if I seat my 45acp - 225LRN handloads with a 1.270" OAL? I have not done a plunk test handgun handloaders often recommend but just extended the bullet so the slide could close. It's an accurate load compared to shorter OALs.

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Assuming it's chambered in a 1911 style pistol, from the magazine, no.

The extractor (conventional 1911 type) is not meant to jump over a cartridge rim, ever. They are to feed up under it from the bottom.
Moon