I have a 1911 Springfield 5" 9mm that I recently milled the slide for Holosun 507K and the slide in not looking back to the rear with Federal premium 115 ammo, I've tried 3 different springs weights 13, 12, 10lbs and three different mags and replaced the slide lock with Wilson bullet proof one and still it's not locking back on the last round, but locks back when I rack it by hand. I guess the only thing left to try another ammo. I'm new to 1911 platform so I'm not used to have the slide not locking back on the last round!