I'm surprised you're getting PF176 with only 7.5 g WAC under a MG 124 JHP.
What is the OAL ?
Can you explain a little more what the "some extraction problems" are ? And, how frequently ?
Were you using this same load before, and the problems just started ? Or, is this a new load ?
Have you recently changed anything about your gun ? Grip, safety, magwell, etc etc ?
WAC is a very common powder to use for 9mm Major and .38 Super Major - shouldn't be the
problem. And PF 176 isn't super high - little bit, but shouldn't cause an extraction problem.
WAC's burn rate makes it an acceptable powder for .38 Super, but a slower powder would be
better - but again, it shouldn't cause problems.
Is the brass new or used ?