I think the slide being hard to pull back this the key.
I did get a bad batch of bullets, They did hit the lands of the rifling.
The slide stopped about 1/8" of going into full battery.
Some I could push the slide forward and others I'd have to pull so hard that the casing flew out, the powder all over the floor and the bullet dropped out of the mag well.
After that I had Extractor problems...... all caused by me.
I guess I'm out of suggestions. Sorry.
Greg