Pop opens can be caused by handloads that haven't been sized properly for the chamber, they don't allow the latch to fully engage the latch shelf. You need to push the shoulder back far enough to allow the action to close completely, if not, the round will protrude from the chamber above flush with the chamber face. That's why the pop opens didn't happen with the factory ammo. Hornady 22-250 ammo is loaded hot, may stick in the chamber in ejector barrels and will make the barrel release hard to press.
Read the Pop open medicine link in the FAQs and the Handi Basics 101 at the top of the list here, there should be enough info there for you to improve the accuracy. Are you placing the front rest just ahead of the trigger guard? That alone will help accuracy, unless you fully bed the forend. I fully floated mine from the stud forward before it shot good, but still shoot with the forward rest up against the trigger guard, it's just normal for break barrels. I've never got good accuracy from a bipod on my fluted 22-250 if that's how you're shooting it.
Tim