Do you have Hogue grips on the 4506 or 457? I would try that, or a rubber grip sleeve over the OEM grip. That way the twisting motion or torque during firing amd recoil is reduced. Anchors the gun in the hand, for me.
Then I would get a bag of snap caps. Put a piece of tape on the wall, around 10 to 15 feet away. Practice basics, to start with. Grip, stance, sight alignment, trigger control. Don't let your finger leave the trigger. Maintain contact with it.
Watch your sight alignment. Does the front sight jog left or right as you break the shot? Tighten that grip a little and make sure that you don't have too much finger on the trigger. The edge of the pad of your finger, forward of the last joint, should rest on the trigger. Practice a smooth, constant steady pull - all the way through till the hammer falls. Practice in DA only till you see that your sight picture is no lomger disturbed before or during the hammer falling.
Once this is accomplished, practice DA for the first shot, then thumb cock the hammer to practice the SA portion. When you feel proficient, get a quater. Lay it on the top of the slide. Now practice your grip, stance, sight alignment and trigger pull without the quater falling off the slide. In DA and SA.
15 minutes of dry fire, every night for a week. You WILL see an improvement at the range. It is cheap practice that pays big dividends.
And don't give up on the 457. I have a hard time being accurate with mine. It is light and slim. Harder to shoot well than the other models. Were I you, I would master the trigger on the 4506, first. Dedicate yourself to becoming proficient with it first, before moving on to the 457. Whether that takes a few weeks, a few months or a year.
I have a friend who is in his 7th month of shooting ONLY his revolver. He is dedicated to improving his skill set. I admire him and his determination and discipline. I have shot with him several times and he is actually pretty good. But he doesn't believe me. He is going to work on his trigger control and only shoot that one gun for the rest of the year. I have tempted him to try some nice and rare pistols - but he is focused and refuses to shoot anything else. Very admirable. He will be successful.
My last suggestion would be to bring that target in from the 25 yard line. In a defensive shooting, if the targets 25 yards away, you should be looking for cover and calling 911. Prosecutors take a dim view of folks shooting others beyond 10 to 15 yards. Ask me how I know that.
Start at the 1 or 3 yard line. Work the basics, just as you did in the dry firing sessions. Then move it out to 5 or 7 yards once you see that you are getting good hits and wearing a jagged hole in the 10 ring. Then go to 15 or 20. If you start getting rounds outside the 10 ring, slow down, bring it back in and work the basics. You seeing a pattern here?
Crawl, walk, run. The results of a determined effort will reward you. Hope this helps! Regards 18DAI