My 45 Shield was completely unreliable and slide stop did not work. It went back to the factory and the slide stop was replaced but the gun could not get through a full mag without a failure to feed. I realized that the last 3 or 4 rounds in the mag feed reliably; the worst were the rounds under the greatest spring pressure from the mag. I fixed the gun myself and it has not missed a beat ever since, but that was my single specimen and may not apply to other 45 shields. If your shield is reliable with the last 3 or 4 in the mag. I would suggest putting something like wheel bearing grease on the center rail part of the slide. What slides over the cartridges in the mag. Mine had cross cut marks on that surface; which I believe are necessary. If your gun functions until the grease is flicked off, you might have the same problem I once had.