Some have trouble with Krauser even in normal and then when it comes time to get him in professional then get some help, or you can do what I did and use the knife. Just dodge his attacks with either A+B or L+R and then when he gets near enough hold down L to get out the knife, aim at his knees and he falls with one slash (instead of 30-50 bullets) and then hit his head, do this several times and you have him beat, just don't stick around to see the bombs go off, you won't live through it trust me I tried.