Alright, this question has been asked a lot and may people dont know the effects or how to detect it.
Blow back usually occurs when your bolt isnt the optimum size for your breach. This allows air get around the bolt and cause air to blow up the feed tube AKA blow back.
1) Disrupted and slower feeding, this can lead to an increase in chops.
2) Minor decrease in efficiency
3) Minor decrease in consistency, leading to a minor decrease in accuracy.
1) Remove you barrel and shine a light through the front of the gun at the breech. If you see the light around the bolt, then your bolt is too small, and you may have blow back.
2) Put a ball in the breech and put a piece of tissue or a business card onto of the feedneck. Fire the gun. If the card or tissue flies into the air, then you have blow back.
There is only really one way to fully cure blow back.
1) Get an oringed bolt. The vapor bolt and bonebreak bolt will both work well.
Some people say that a HALO will cure blow back, but it wont help with efficiency and consistency.
So to sum it up, get an oringed bolt.
They can be found at