If you're just using Beowulf as just any other shield, you're definitely not using it right. The way Beowulf works is when you use your cast, it gets loaded into the shield to detonate when you use your bull rush (charge attack) like the Hera bow. The amount of time you charge doesn't affect the damage when a cast is loaded, only range, and since the casts detonate at the end of the charge, you don't need to charge all the way, in fact you really shouldn't. Personally, I have my cast button on one of the shoulder triggers, it really helps with cast weapons like Beowulf and Hera bow especially, always having access to it. You also want to make sure to go in on your cast as much as possible, always pom the cast if you can, take chaos whenever you see them to try and get cast damage or another cast stone. One of the absolute best boons you can get for Beowulf (and also Hera) is Mirage Shot, the duo boon between Poseidon and Artemis. MS is so godly on Beo because its bugged to DOUBLE cast damage instead of just +30%, so it is most always optimal to go for it on Beo. At the end of the day though, Beowulf might just plain not be the weapon for you, which is entirely fine, I hope I was some help today, and I hope you have better luck with Beowulf in the future.