....the instant the gasses start expanding from burning the powder the projectile starts moving one way & the gun the other. Both have reached their maximum acceleration as the projectile clears the muzzle. The escaping gasses does play a small part to accelerating the gun Just a Wee bit longer than the projectile....
No big deal here Miller. I think, when the bullet, and gasses, clears the muzzle, it probably reached maximum velocity, not maximum acceleration. It might be like riding in a car, when it's going at a steady speed, you can't feel it change speed, or accelerate.
