Leather seal is modern

[WD Feese]

 Today I  completed a take down, cleaning and lubing of my pre- saftey HW 35 and afterwards shot it over a chronograph.   After that I  got out another pre-saftey 35 which has been changed to a modern seal and I have been told it has a vortex kit installed as well.
  Shooting JSB 8.44 pellets both rifles shot at 7.9 foot pounds.  No gain for the change.  This topic comes up from time to time so I thought I would share.

[Roadworthy]

I don't know that the synthetic seals are superior to the old leather ones - at least the leather ones that haven't disintegrated.  I do know they're more available.  You can order them but I don't think you can order a new leather seal.  Leather sealed guns are usually lower powered guns.  I know of no newer leather seal guns putting out sixteen or more fpe and perhaps not even twelve.  I do have an older Diana 35 with a leather seal.  it's 56 years old and it still shoots accurately.  It's no powerhouse but it's a reliable little rifle if I add a bit of silicone oil to the seal from time to time.

[Toxylon]

As I understand it, Diana 45 is the highest-power leather-sealed production gun around, peaking at just around 16 fpe in the bigger cals.

Old HW35's have not only leather seals, but shorter strokes than the later ones. When an old, leather-sealed HW35 is modified for a synthetic seal, the adapter on the piston shortens the stroke further. So, a possible increased efficiency of a synth seal would be offset by the decrease in stroke (almost nothing affects springer velocity as much than stroke length).

If the piston itself was switched to a modern one, a leather seal would not be possible to use on it. So, the results by WD seem inconclusive.

[Toxylon]

Too late to edit, but:

If an old HW35 modded for a synth seal shoots no faster than an old HW35 with a leather seal, it means the synth seal IS more efficient than the leather seal, but the mod doesn't allow it to show on the chrono, as per WD's result.

So, there's no gain from switching to synthetics with an old HW35, unless you switch to an altogether new piston.

[subscriber]

I suspect the leather seal feeds a small amount of oil mist into the compression chamber, and that some fraction of that burns to add a little bit of power.  If you use non-combustible oil, or a synthetic seal, you will probably lose power.

Dieseling is a swear word in the context of springers, yet I think it was common for leather sealed springers to make a quarter or a third of their power from "controlled oil consumption".  Hence the need to re-oil the leather seal from time to time.

[Toxylon]

Yes, leather-sealed guns depend on 'controlled dieseling' to do their job. It doesn't deteriorate their consistency or durability like it does with synth-sealed guns. Although it must be said that I have had very consistent, well-mannered synth seal guns, too, that are demonstrably dieseling.

[MDriskill]

Gents, I recently had a leather-sealed 1980-vintage HW 35 apart for work...here are some random comments you may find of interest:

+ The gun in question was shooting weakly, so I wondered if its piston dimensions were typical. These notes from the BBS forum on that subject may be of interest: https://airgunforums.co.uk/threads/hw-35-piston-dimensions.125165/

+ Studying the pics in the BBS thread, my leather-sealed piston looks typical, but later plastic-sealed ones may have a shorter sear rod, which would definitely increase stroke - but I'm not sure, don't have a dimension for that.

+ Here's a pic of the gun's piston. The leather seal is 12mm long:


+ On my gun, the seal's attachment screw's head was 10mm in diameter and recessed about 4mm. This is a chunk of "lost volume" air - maybe about the same as the transfer port? - big enough to affect velocity. The flush face of a plastic seal would eliminate this.

+ This photo shows an HW 35's 30mm factory plastic seal, and adapter for converting a leather one. When assembled it's 15mm long, so as Toxylon noted, this reduces the stroke. It's also quite heavy.


+ The other seal and adapter in the photo is a Vortek set for a 25mm Weihrauch piston. It's only 11mm long when assembled, and quite light. I don't have one of their 30mm ones but if it's similar, the change in stroke compared to leather might be negligible.

+ Last but not least, conventional wisdom says that older leather-sealed HW's have a 4mm tranfer port, and plastic-sealed ones a 3mm port. This is true for all the old leather-sealed HW 30/50/55's I have, but surprisingly - NOT for the HW 35. All three of mine are leather-sealed; the oldest (1967) has a 4mm TP, but the other two (1973, 1980) have 3mm ones. That's a head-scratcher - might it be related to the 1970 law restricting power to 7.5 joules/6 FPE in Germany? The 35 was HW's only model that could significantly exceed that in those days...

[WD Feese]

The subject was supposed to be leather vs modern.  Modern technology changed vs to is.  Noticed this after the posting.
  The only point of this posting is there was no velocity gain for the trouble and expense of the change. However as mentioned above availability is a factor unless one is willing to make a leather seal.