Hiya Baz,
The heads on both '45s are plastic (they are 110% not leather). These heads were certainly marketed and bought as being of ptfe. I am no expert on this so must assume they are. They are not the only guns I have them on. I have lost track all together but think I also have them on a couple of Anschutz 335s, an Original 50, a 50T01. I think the only gun that ptfe didnt work that well on was an early 35- but I was warned the business end of the compression tube was ever so slightly constricted on these. As you say ptfe is pretty unforgiving in that sense. I can only speak from experience and all the guns I have fitted these heads to work fine. I have stripped one or two over the years after some amount of shooting and have not noticed any degree of distortion.
I would say though that if I was engineering minded I would turn a steel piston head converter to revert to the later Diana standard piston heads. I know many would say that is moving away from originality but I have had a couple of instances where leather heads have expanded and sapped power dreadfully. I know power isnt everything- but if we have been given 12 ft llbs then I want to use it. Then again I dont punch holes in paper or shoot HFT. I recall on Anschutz 335 I purchased had a new leather head fitted by the previous owner and it had been soaked in oil and had siezed the gun solid. Plastic (ptfe I assume) soon had that one shooting sweet
Sorry for the thread hijack Nickos. I hope you get this '45 punchy and accurate
As I say- I am not an engineer- I just speak as I find and from my experience.
Dave