Secondly, it is the very reason why reloads are warned against in the manual.
Third, glad it was not your own home brew and I would be in contact with that ammo reloading outfit and request that they cover any costs out of your pocket as well as any lower value of your USP if it is now combining mismatched serial numbered parts.
It is always fantastic how HK USA stands behinds us with great service and warranty support. I imagine the warranty was not in play here since the reloads were used but that does not mean that HK did not step up regardless, however you did mention a fee.
This is the very reasons that reloads are a danger at all times.
Some may use range collected brass and with that source, it is never known the number of times the case was reloaded or the pressures that it was reloaded to.
With new brass, the OEM is aware of the manufacturing and quality control processes. That is out of of the control in re-manufactured ammunition.
It may not blow up often but does one want to lose their fingers if they were the loser in a less common but very catastrophic failure?
For the bit of savings that remans may offer, I find the value of my phalanx greater than any saved pennies and I will gladly pay out the extra coins.
I realize that many remans are sold and used often in mass quantities but they are just not my choice, ever.
I am also glad that this did not happen to you while shooting a lessor brand fierarms or you may not have been able to type this post for many to learn from.