[DonVoigt]

It is the "energy" not the weight- weight x velocity squared = energy; so the velocity has much more effect than the weight!

The hold open should be high with an empty mag, the mag button pushes it up to engage the toggle.

What it sounds like is you have a good mainspring and was shooting "weak" ammo, if it did not lock open. With the 147gr you have more energy to compress the spring fully, and it locks open.

You can't decide if the main spring is too strong without more info.
If the hold open does engage with the empty mag, and then release when you remove it, there is likely nothing wrong with the hold open.

You may also be limp wristing the pistol, which will cause the same failure to lock open some times and not others. Try a "stiff arm" stance and pay attention to it.