FCAW X-Ray Test Question

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Hey all, I am a student of 6 months getting ready to take a FCAW X-RAY test for a ship yard job. The test is on 3/4" steel, 16" long, a 30 degree bevel on ceramic backing. We have a four hour time limit to complete both horizontal and vertical pieces, so reliable settings are crucial. Right now, myself, and my instructor have been beating our heads against the wall trying to figure out why we continue to get undercut on all root passes on the horizontal. While the undercut is only on the bottom portion of the weld, and it is very, very tiny, we know that it will be picked up on the X-RAY. We have been running everywhere from 22v to 26v on a constant 300 wire speed and still come up the undercut. We also have been running roots on everything from 1/4" steel to a full 1" with the same results. The front end of the weld is flat, washed in top and bottom and perfect in every way, but the back end is deceptive and continues to "fail". The ship yard's recommended settings are 30-33v, which we have tried, only to yield massive beads that do not adhere to the 1/8" stickout rule. Is there anyone out there who would know reliable techniques and/or settings that allow for equal penetration on both sides of 1" steel without getting undercut of any kind?  Thanks!
Reply:Smooth or grooved ceramic backing? Gap? land? preheat?Syncrowave 180 SDMillermatic 250XSnap On MW 120 Econopac 50Victor O/A with some Smith Attachments 30 X 50 shop with a 400 Amps