Are the notches on choke tube standard or are they different with each gun manufacturer? Any help would be appreciated.
There are a few different schools of thought on what the notches on choke tubes are for, but the most common explanation is that they help to align the tube with the barrel. Over time, barrels can develop a slight bit of differential wear and tear, which can lead to misalignment between the two. The notches provide a way to ensure that the tube lines up properly with the barrel, which in turn helps to improve accuracy and patterning.
Another explanation is that they serve as vents, allowing gases to escape to prevent strain on the internal components of the shotgun. This can be especially important when using high-powered shells, as the increased pressure can put a lot of stress on the gun.