The advice is wrong and right...
The problem with PTFE is its coefficient of molecular expansion/ contraction in relation to heat...
...as opposed to its lowest known coefficience of friction....which benefits it.
What is really required , if you do use PTFE is a micro lip that can flex to the altered states of temperatures..
The TR Robb washers available for the Walther LP53 etc can bring almost a 50 fps increase (in the case of the walther) but be prepared for 2 zero points when homing your sights in.
One for cold morning temps and one for when temps have warmed up....Its 2 clicks up in the case of the Walther at 10 mtrs....on a warm day.
This is because the piston head has expanded and the velocity dropped due to expansion.
This is most noticeable in the summer months but we have had some eratic temps this autumn....it can play havoc...
To overcome this problem we can machine a lip....by backing off the washer with an angle of 7 to 10 deg on the compund slide from the front edge ...
For example i do my Walther heads at 23 mm at the major dia front edge and backing off to 22.50mm on the back edge that sits on the piston front face....
If we then machine in a slight dish front face of 0.2mm leaving a major dia. witness of 0.25 mm we get a flexible lip....it works pretty well...
At stable temperatures the Walther has almost no velocity variation....a mind numbing 2 fps difference shot to shot...i was staggered at first ...as does the inefficient Tempest pistol.....running 4 fps shot to shot on a PTFE ring..
My club members all holding one zero regardless of temps ...running modified Robb heads..
So ....dry firing..
Well it will certainly seal your gun alright but likely over expand it for on hot days....and the usual reason HW45s struggle to match some pistols in accuracy terms without major re-working....
Get her running right and the group suddenly shifting one day for no apparent reason...
The 45 head is pony ...and needs reworking ....but i agree with Tin ...its prob best dry fired from new ...or it wont seal up for a while until finally bedded..
More to this piston head business than meets the eye....25 years of playing now.
The notes on alternate seal materials to negate this problem creates other problems....ive played extensively with Urethane parachure washers....modifying and making new ones which do not suffer so much from thermal expansion and are more soft and pliable in nature ....but they do rob power ...can parachute out too much in some cases and tend to grow constantly outward over time ..
Fine for rifles but cost us velocity in pistols