Well, I'm glad it worked out well for you. I am a little confused about the nut and washers on the 3/8" rod, if you don't mind additional explanation or showing a photo. Were these pushed against the muzzle, and the nut turned with a wrench to pull the ball?
One thing I do believe is that all ball pullers are not created equal. I like the ones from Track of the Wolf:
View attachment 260731
The screw has a murderously sharp point and threads and a tapered shaft. A lot of manufacturers just use a wood or sheet metal type screw, but I honestly believe these purpose-built ball pullers from Track are superior. That screw really bites into the ball and holds securely.
This ball puller also has a collar fitted to the bore size. This keeps the screw centered, and prevents it wandering off and scoring your bore. Several of the ball screw makers produce this item with a centering collar, but as far as I know, only Track uses that kind of screw. I don't know the caliber of your rifle, but the 3/8" threaded rod would be .375" in diameter and in a .54 caliber rifle (for example), you would have .165" of "play," which is quite a lot. If it were mine, I think I might wrap a few layers of tape around the threaded rod just above the screw, to serve as a centering guide and protect the bore.
The ball puller from Track fits on a regular ramrod or cleaning rod. This does require hand-pulling the ball, rather than the nut and wrench system on the threaded rod. I imagine that nut-and-wrench system enables a straight and powerful pull with little effort. That's a good idea.
Just brainstorming here, but if the T-handled 3/8" threaded rod could have the end bored and tapped to 10-32 to accept the Track of the Wolf ball puller instead of having the screw welded on, you would have the best of both... the purpose-built ball screw with the centering collar, and the nut and washers for strong and well-controlled pulling action.
In any event, it sounds as if the home-made ball puller did the job.
That's good news!
Notchy Bob