I have not read this whole thread, however the store does have (one) opportunity to rectify the issue before you are entitled to a refund or replacement.
A serious fault would be a major issue, the gun blowing up or going full auto or doing something very dangerous etc. Failing to feed or eject a few rounds of specific types of ammo would not be deemed a "serious" fault.
If after the "fix", if you still have issues then you are entitled to a refund or replacement.
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