The main downside of any delayed blowback system compared to gas operated systems is that it doesn’t actually lock close, it merely slows the backwards movement of the bolt at the beginning of the cycle using mechanical advantage. This causes bulged cases and more difficult extraction with high pressure ammo. You also get higher bolt speeds with higher pressure, creating bolt bounce issues.

You can still run delayed blowback with rifle ammo using clever design (fluted chambers, anti-bounce mechanisms, etc) but gas operation is more sensible