Mainspring does not have much effect on feeding. Correct me if I'm wrong Gents, but the weak mainspring will not absorb the recoil, and the pistol will slam in the back, peening the frame, and/or ramps. Too stiff mainspring will cause the weapon to "short stroke", and the fresh cartrige will not be picked up from the mag. Also,....too strong spring might not allow the breech to travel far enough for the empty case to hit the ejector with sufficient force to be ejected, thus it will stay "hooked" on the extractor, and travel back misaligned, causing the classic "stove pipe".
"Nose up" (if I understand you correctly), is the loaded cartridge jammed between the breech block and the chamber? (failure to chamber)
That's usually caused by the weak mag spring, damaged mag lips, or damaged follower.
Try changing the mag, and forget about the mainspring for now. I would also inspect the frame rails/bolt rails, and check for burrs, damage, being tweaked, and such. Put the upper on the frame (don't hook it), and slide it gently back and forth to feel for binding.
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