If you own any type of Automag with a stainless steel body, then you use nubbins as your ball detent. They mount on the barrel. The old version is the wire nubbin which did the job but eventually the plastic nubbin was made and released. Since the wire nubbin was around for a very long time, some companies that made aftermarket barrels for the Automag didn't feel the needed to pay too close attention to detail. For this reason, on some aftermarket barrels the nubbin groove is slightly different so the new plastic nubbin doesn't sit properly. By all means upgrade to plastic nubbins but if you notice that you are double loading, or you get radical velocity drop-off, then there is a chance that your nubbin may not be doing its job. In this case switch back to wire and see if the problem goes away. When using wire nubbins, at the first sign of chopping, always check that the nubbin has not broken.
Wire Nubbins
Plastic nubbins
If you own an Xmag or any mag with a ULE body on it, then that means you have switched from nubbins to ball detents. The threading for the AGD detents is the same as the Angel. However, the AGD detents are made with a slightly larger bore around the ball. This gives the ball space to move rather than jamming up when a bolt with a higher boltspeed hits it. Even if you own an Angel, I highly recommend buying AGD detents. They are also insanely cheaper than other detents sold for the Angel and perform much better. If you are double loading or getting severe velocity drop off, your ball detent may be too far out. If you are using the level 10 and constantly hearing the level 10 kick in, the detent may be too far in(or your level 10 is set to be too soft), back it out a bit(to keep it from unscrewing when backing it out, wrap the threads in a bit of teflon tape). Whenever you chop or break paint, check to see if your detent ball has not broken.