Dry firing an HW45 to size the piston seal...

[averageplinker]

Where did this advice originate?

Hi all,
I am enjoying my Kempton airgun fair bought HW45, however as is often noted for these pistols she is a Smokey old bird. Whilst this backs up her almost unused appearance I would like to rid her of this filthy habit. I checked the online owners manual and found no recommendation from HW to dry fire twice to size the seal. So where does this advice originate? And if you have tried it please advise if it worked or made no difference to your HW45?
Cheers
Rich

[bighit]

i remember dry firing my HW45 once . accidently . the pellet did not go in right when i was firing it with out looking while loading (silly i know) it fired and a puff of smoke came out . when i opened it to reload the pellet was still in the gun. sitting next to the barrel and the bit where the barrel screws are.

it smoked on almost every shot if i remember right . i bought the pistol new and had it open once but i never lubed it or cleaned it internally.

you could tell it had been fired due to the smell it made when it was fired .

[Mark A]

I did the dry firing twice thing after seeing it mentioned on here and it didnt do anything to stop it smoking. It made a loud bang with a lot of smoke twice and that was about it.

[Phil Russell]

Apart from dry firing not being a good thing I cannot see how it would help anyway. I know that dry firing is maybe not so bad as we all used to think but I still can't bring myself to do it, for whatever reason.
And, thinking about it, a snug fitting seal could actually promote smoking due to the more efficient pressure, and so heat, developed. Then again, maybe a loose seal would allow more lubricant to migrate in front of the seal. Why do you think the seal is loose? Is the power down? Remember the HW45 is a dual power pistol.
I guess the only proper way to eliminate smoking is to strip it down to clean excess lubricant away. Or, as most reviewers seem to do in the magazines when reviewing a new gun, ignore it until the excess lubricant is used up. So ... if your pistol is virtually unused you may prefer to ignore the smoke for now. It smells good anyway ....
Cheers, Phil

[tinbum]

I dry fire twice on rebuild, it won't stop the smoking, its all the grease you remove while its apart that does that. The seal is a hard PTFE and dry firing helps to expand it to fit the chamber.

I have written a picture heavy article on stripping and fettling the 45 which will be in the next issue of Airgun Shooter

[Phil Russell]

I have written a picture heavy article on stripping and fettling the 45 which will be in the next issue of Airgun Shooter

Excellent .. another guide for my collection. I look forward to seeing it.
Cheers, Phil

[averageplinker]

I dry fire twice on rebuild, it won't stop the smoking, its all the grease you remove while its apart that does that. The seal is a hard PTFE and dry firing helps to expand it to fit the chamber.

I have written a picture heavy article on stripping and fettling the 45 which will be in the next issue of Airgun Shooter

Do you know when the issue with your strip guide is due to hit the shelves? A must buy for me now!

[clarky]

Where did this advice originate?

Hi all,
I am enjoying my Kempton airgun fair bought HW45, however as is often noted for these pistols she is a Smokey old bird. Whilst this backs up her almost unused appearance I would like to rid her of this filthy habit. I checked the online owners manual and found no recommendation from HW to dry fire twice to size the seal. So where does this advice originate? And if you have tried it please advise if it worked or made no difference to your HW45?
Cheers
Rich

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

[tinbum]

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 ...

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....

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

So that's a yes?

[averageplinker]

Well after all this advice I think I am just going to shoot it and if she continues to smoke after each shot I will just blow across the end of the barrel muttering dirty Harry and cowboy film quotes 😀

[clarky]

So that's a yes?

just the once maybe tinny...
Tbf ive not tested how many times and what style of PTFE seal is more ...or less suited to dry firing ...but the thick plain lump on the 45 probably benefits a punt without a pellet first time of fitting.

[NewPaul]

I bought my HW45 second hand and don't know if the previous owner(s) carried out the two dry fires so, if I do it, that will be four dry fires. Is that ok ? And, if the fella I got it from also bought it second hand and it was twice dry fired by the previous owner(s) that would be Six dry fires. And, if that bloke bought it second hand.......

[tinbum]

I bought my HW45 second hand and don't know if the previous owner(s) carried out the two dry fires so, if I do it, that will be four dry fires. Is that ok ? And, if the fella I got it from also bought it second hand and it was twice dry fired by the previous owner(s) that would be Six dry fires. And, if that bloke bought it second hand.......

Paul, I think you're overthinking this!

How's your willy?

[NewPaul]

Paul,

How's your willy?

In need of a new Aussie seal and a bit of bum slide

[clarky]

I bought my HW45 second hand and don't know if the previous owner(s) carried out the two dry fires so, if I do it, that will be four dry fires. Is that ok ? And, if the fella I got it from also bought it second hand and it was twice dry fired by the previous owner(s) that would be Six dry fires. And, if that bloke bought it second hand.......

...its probably so expanded in diameter and thus slowed down so much that it wont care ....pellets, or no pellets ..