Look what Israel just invented for urban warfare
https://www.youtube.com/watch?t=64&v=cjRxkem9oz4
Did you see the effect of recoil?
This might be a good way to break a barricaded door, but it seems like it will wreck the rifle if it is used often.
The English had a rifle grenade that they used a lot in WWI that had a similar bullet trap propulsion, the soldiers would keep a rifle separate just for firing the grenades, they would wrap the stock with wire and never fire it off the shoulder, the accuracy as a rifle would be degraded.... . And this is the Enfield , a very stout rifle.
The M-4 is designed for very manageable recoil, so defeating its recoil system to throw a grenade door breaker seems likely to wear it out shortly.
Still might be worth it , depending on the situation, might be a good idea to use up a rifle.
