I would measure the headspace of my ammo and look for scuffs on the body. Especially the ones that will chamber and those that won't. It doesn't take but a few thousandths to keep you out of battery if the factory ammo is close to zero headspace to begin with. That may be within the variation of your ammo, factory ammo usually has a few thou of variation in headspace. You can also dump the powder and shell out of one that won't chamber and size it with a die and see if that fixes it.