The powder you are using is way too fast for that launching platform. 2400 is about as fast as you can go, and get away with it. Way too much room in that case for unique, or bluedot. H-110/Win.296, H-4227, even some of the fast rifle powders work. You want a full case.
Oh, another thing. NO LEAD. You want a case setback, you will get it running lead bullets. Jacketed only. Lead is usually .001, to 002. sizes larger than the diameter of the bore. You are pouring tons of pressure into that little bitty .357 bore, with a .44 mag. boiler room. The back of the bullet turns to liquid, and successfully washes the forcing cone, and the first 2 inches of your barrel, with lead. Now, you have reduced your bore size from .357, to .355. Guess what, unless you are using 9 mm bullets, you have a real live pressure problem. So, case setback.
If, you are so inclined to run some semblance of lead. Get you a bunch of pewter and a .41 magnum mold of the heaviest bullet weight you can get. Then, find a .357 diameter bullet swedge. A 240 gr. .410 bullet cast out of pewter will grain out at about 130 grs. That sucker is rock hard. Only problem is, they explode on almost anything they hit. They do not lead. They also Brinel out at about 24. They are a royal pain to cast. Mold has to be really hot, and so does the pewter. I know bullets for reloading are scarce, but hunting jacketed bullets is a lot better than casting pewter.