Have you tried pulsing yet??? ;) In other words, GMAW-P??? Which specific grade and UNS number of Stainless steel according to this are you using for the bracket???
http://www.hcss.com.cn/en/image/DIN_EN%2010088-3%28995-08%29.pdfNow this is to be welded to AISI 441 shell which is a ferritic grade of Stainless steel, yet you didn't elaborate which specific grade under DIN 10088 is the bracket... So if the two members which make up the joint are dissimilar, then E 307? may, or may not be the correct wire, or it is but your weld parameters, your work angle which should be favoring the thicker of the 2 members is not correct either...
What type of specific joint configuration are you using? Have you tried using a little more helium in the shielding gas mix than 3%?
Once again, have you tried welding the joint with pulsed spray transfer GMAW-P (Gas Metal Arc Welding-Pulse) at all??? What about "Accu-Pulse, Accu Curve, Accu Speed" or "RMD" because, that power source gives you those capabilities and more!
http://www.millerwelds.com/products/automation/auto-axcess_systems/http://www.millerwelds.com/pdf/spec_sheets/AU8-0.pdfNot to be disrespectful, but you have one heck of a power source to work with and from what I' have read in your post, you're not telling us anything about whether or not you're utilizing any of the advanced features that come with your power source such as the MIller Auto Axcess 450 DI... So if you could elaborate more on the specific settings you're using, then we might be able to steer you in the right direction. ;) I would also like to suggest that you contact your Miller Rep to see what they can do to help also. ;)
Respectfully,
Henry