Help with Crossfire 4500.....

[50 cal]

4500 psi Crossfire keeps blowing nipple seal.
If I tighten it just a little, it won't fill. If I loosen it just a tiny bit, it will blow the seal in the fill nipple after it fills.
What the heck is going on?

Thanks AO.

[PyRo]

Maybie you have a bad batch of seals, or ones not made for that pressure?