Junk the acetal, it flexes and worthless for its intended purpose.
the only reason acetal is raved about and used, think logically and between the lines. Its marketing! As in 5 min job as a one off for an HW80 in delrin, but same machine using steel looking at 1 1/2hrs, see where i'm coming from people are mugs and believe the marketing.
Then add delrin isnt stable in size, has more grab therefore more friction as the spring gouges in to it with greater surface area.
Prone to breaking as well, certainly with 10mm+ bore and 13.5mm+ o/d = 1.75mm thk wall 2.1mm tops!
Then add it flexes not keeping spring in a straight line, what you dont want.
Steel would have less friction due to lesser surface area and coeficient of friction any way. You tried moving a ton machine digging in to soft material such as wood or delrin, it dont slide. Using steel to steel machine slides easilly, similar to the compressed spring wanting to buckle or veer off!
Anyone with any engineering practice will agree to highest level.