Wesley Salmon wrote a critique of critical rationalism in which he claimed this it could not explain why it is rational to use the predictions of scientific theories to help us make decisions. First, note that Salmon does not and cannot refute Popper’s criticism of inductivism. There is a very simple reason for that: the criticism is valid.
Second, Salmon states (p. 11) that Popper once wrote that a realist will think there are regularities in the world. Realism, by Popper’s lights, is a conjecture and should be treated by the standards of any other conjecture: that is, it should be retained if it can withstand criticism. To be an inductivist, Popper would have to hold the opinion that observations imply something about the future, but of course this is not implied by the statement that there are regularities in the real world. Observations plus the laws of physics may imply something about the future, but of course that cannot tell us about the status of our knowledge of those laws.
Finally, critical rationalism does say things about what sort of predictions are rational: those predictions should be made in ways that have so far withstood criticism and should be easy to criticise if they go wrong. Furthermore, we should take steps to make our predictions and practical actions easy to criticise. We should also take steps to respond to the criticisms we receive. So, for example, when planes are built the best available theories of aerodynamics will be used to constrain the design. Why? Because if we didn’t we would have an unexplained discrepancy between our explanation of why we chose a specific plane design and the best available theories about the real world in which that plane will operate. Those aerodynamic theories are in turn retained because they stand up to criticism, solve problems, explain things that other theories don’t explain and so on. Some of the components, or models of those components, may be tested in wind tunnels. The plane carries a black box that collects information about the plane during flight in case something goes wrong so that it will be easier to criticise the performance of the plane’s components. All of this involves only conjecture and critical argument and it is rational by Popper’s lights.
This procedure is not rational by Salmon’s lights because he is a justificationist – he thinks that decisions can and should be proven right or made more probable to work or something like that. However, he doesn’t produce any proposal for how such justification could be had and there is a straightforward logical argument that indicates that this is impossible. That is, any argument uses premises and rules of inference and its conclusions are only proven or probable if those inputs are proven or probable. How are we going to show the inputs are proven or probable: another argument with more premises and rules of inference that have to be proven or shown to be probable? Seems to me that would lead to infinite regress and to no decisions ever being made. This is supposed to be practical?