First of all I know nothing about ammunition, but I do want to comment on how you're getting your results and how you're making your claims. I'm no statistics whiz, but I do know that you're basing your opinions off an extremely small sample of bullets fired. While five out of 50 seems to point to Winchester being poor quality, you also stated that out of 400 previous shots only 2-3 failed to fire. That's incredibly low - you even said so yourself. I would base my overall opinions off the higher sample (400 bullets) rather than the marginally lower 50. According to the law of large numbers, the larger your sample becomes, the the closer to equilibrium your results will get to (thus the more accurate your results become).
I'd say you lucked out and picked up a bad box when you fired the 50 rounds. You would have to fire a good many more rounds before you could achieve a true representation of the quality of Winchester ammunition. If you don't plan on firing anymore, then base your opinions off the 400 rounds fired and not the 50.
EDIT: Also you have numerous lurking variables which will bias your results, including the manufacturing environment of the ammunition, the packaging procedure of the ammunition, the quality of the pistol, the current condition of the pistol (is it damaged or misaligned?), the condition of the ammunition when fired from your gun (did you leave it out in an unsatisfactory environment for too long, is it damp or wet?), etc. There are many factors, many unseeable, which affect the fail rate of the ammunition.
Just my two cents.
EDIT: But to play devil's advocate with myself (that's kind of odd and scary I suppose) if the misfiring is creating an unsafe situation (which is it obviously is) then it would be smarter to switch ammunition brands just to be on the safe side and prevent any unneeded injury.
Good luck and have fun

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