Its been many years ago but I fired a 3.5" Rocket launcher. Realize of course this is nothing but an open tube to guide the rocket & has no closed breech. There was a definite forward pill from the friction as the rocket went down the tube. As it cleared the muzzle the ejecting gasses would give a slight rearward thrust to the tube from contacting the bell placed on the end to protect the firer. I can feel the barrel movement in a long recoil gun such as the A-5. Other than these two examples I have never felt anything but one continuous push. Realize that 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.
The projectile has obtained its Muzzle'V & the Gun its Recoil'V.
"IF" for instance the projectile has reached 1200 FpPS & the gun perhaps 15 FPS, then the projectile is traveling 80 times as fast as the gun. This has all occurred in less than .003 of a second during which time the projectile has traveled the length of the barrel & the gun something on the order of 5/16-3/8 of an inch.
Built in Inertia/Momentum carries both for the rest of their travel. Sure if you have a significant difference in "Measurable" recoil you can feel it. When it comes to "Feeling" differences which cannot be measured, I will just say "The Power of Suggestion" is very strong in a lot of people.
