50 Beowulf reloading question

[ncwg2boatguy]

Loaded up some 330gr 50 Beo ammo last weekend using Alexander Arms load data. Cycled fine and was pretty accurate but upon inspection I noticed discoloring down one side of the brass like powder blow by? Whats up?

 

[Redd508]

Pressure can be high enough to cycle the action but not high enough to expand the brass and make a good seal in the chamber. Assuming that you aren't using max load data you can try increasing the charge until you get the results you want.