I think if a gun won't seal with a hand pump then the seat isn't finished well enough.
Which means the valve seat and poppet are not of proper manufacturer.Otherwise the guns should be sold with a caveat, "Warning, Cannot Be Filled From Empty Without Specialized Equipment!"
Joe had all calibers for Impacts a couple days ago...that could have changed by now.
Only other place you might check is Krale, sometimes they have stuff that others don’t.