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MPX won’t go together

566 Views 5 Replies 4 Participants Last post by  littlejacks
So I have a Gen 1 SBR’d lower and I bought a MPX K upper and put an In Lead We Trust barrel on it. The new upper has a tail on the back of the recoil spring plate and it won’t go into the upper far enough to close the two receivers together and push the pins in. Even with the old barrel or even without the bolt and charging handle. It just won’t go in anymore. What am I doing wrong?
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This may sound stupid but is the recoil spring in backwards? The “tail” may be the Op Rod. Pics would be very helpful.

The above link shows SIG MPX bolt carrier assembly, SIG website, and it comes with two tail pieces. One with a tail, assembled in Photo, and the other as a separate part in third photo.
OK, I need a different tail cap then. I got my assembly from a gun so it didn't come with the other style. I'll call SIG. Thanks for your help!
I might just grind it off
I might have a spare without the tab. Can check in a few hours
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