There are several physics equations (some I linked to in the article) which discuss this topic. One of the main takeaways I learned from running this experiment and doing some of the math was that my rifle is 900x heavier than the bullet, which is why it is able to accelerate so much faster and leave before the rifle/barrel move at all.

It does bring up a good point though, which I'll cover in the article where I deep-dive into the physics: Knowing the acceleration of the rifle, I should be able to calculate how far it has moved in the same amount of time it took for the bullet to leave.

Thanks for taking the time to read it, and for your feedback!