V-Mach seals

[Jonas]

Evening,

can someone explain to me the idea behind V-Mach seals being such a tight fit?

I bought a V-Glide kit some years ago, fitted it straight to my HW97 .177 and today, several thousand pellets later, it is still very "sticky". The cocking lever wouldn't fall under its one weight when the gun is cocked.

[Murphy]

Yeah there mass produced and made big because every gun is slightly different.

[Murphy]

Same reason all Titan springs are too long.

[tx200hc <3]

Very satisfying when you make them fit just right.......Takes a blimmin long time.....

[Loki_79]

Several people on here have reported that Mr Pope has advised them that the seal does not need re-sizing as it is supposed to be snug. The following is purely my speculation, but I think there are two reasons.

1) Every gun is different. A standard part must seal the largest bore, resulting in a tighter fit on some/most guns.

2) As a measure to reduce the piston bounce without increasing the transfer port diameter. I.e., If you make the piston a perfect fit, you also have to make the transfer port the perfect size - too big and the piston will slam, too small it will bounce. Having a tighter seal increases friction and requires a slightly stronger spring, both of which suppress potential piston bounce and the resulting recoil is the nice dull thud that everyone likes.

[Rickenbacker]

Recent thinking seems to be to avoid sizing them down these days. I think JT did an article in AGW about it recently. Something like - They're best if seasoned and simmered in boiling water for 5 minutes, like petit pois

[barrel]

Never had one that did not need resizing, all have been very tight. In order to make the rifle usable they had to be resized.

Kindest regards

Barrel

[tx200hc <3]

If you don't resize them they come off when you cock the rifle...... and if they don't they give you about 5fpe for a few shots and then come off!

[u.k.neil]

I have fitted many hundreds of these kits over the years and never had to size one down yet and never have one come off either. When fitted correctly and properly lubricated I have found that the majority of kits give around the 11 f.p.e. with no additional washers or spacers, and the odd one needs either a couple of the steel washers at the front of the top hat or one of the Delrin spacers behind the spring on the guide.

They do "bed in" after a few hundred pellets through them and rise in muzzle energy around 0.3 to 0.5 f.p.e, that's why I tend to set them at 11 f.p.e.initially.

Neil

[NickG]

Several people on here have reported that Mr Pope has advised them that the seal does not need re-sizing as it is supposed to be snug. The following is purely my speculation, but I think there are two reasons.

1) Every gun is different. A standard part must seal the largest bore, resulting in a tighter fit on some/most guns.

2) As a measure to reduce the piston bounce without increasing the transfer port diameter. I.e., If you make the piston a perfect fit, you also have to make the transfer port the perfect size - too big and the piston will slam, too small it will bounce. Having a tighter seal increases friction and requires a slightly stronger spring, both of which suppress potential piston bounce and the resulting recoil is the nice dull thud that everyone likes.

It also makes the gun inefficient, more spring and tighter seal increases recoil, you want minimum friction and less spring, faster is better.

[Herx77]

I used to machine new weihrauch seals to suit my 77;then talking to Steve about the variability of my results,the hybride seal happened. It is flexible enough initially in its operation to ensure a good loose seal, and control run away acceleration,using the back pressure of compression on its flexible seal lip to regulate how good that seal is.
HERX77 .

[tx200hc <3]

I have fitted many hundreds of these kits over the years and never had to size one down yet and never have one come off either. When fitted correctly and properly lubricated I have found that the majority of kits give around the 11 f.p.e. with no additional washers or spacers, and the odd one needs either a couple of the steel washers at the front of the top hat or one of the Delrin spacers behind the spring on the guide.

They do "bed in" after a few hundred pellets through them and rise in muzzle energy around 0.3 to 0.5 f.p.e, that's why I tend to set them at 11 f.p.e.initially.

Neil

I had it happen with one of the red gamo ones first so when it happened with my green vmach (are we talking about the right seal?) i knew what had happened and didn't fire the rifle.....The gamo one went in the bin but the vmach was fine after the piston had several wizz's in a leccy drill and the seal met several sheets of wet and dry..

[Loki_79]

It also makes the gun inefficient, more spring and tighter seal increases recoil, you want minimum friction and less spring, faster is better.

I know that, but the point I am making is that for a mass produced kit you will broadly get better results with a tight seal and more preload. Yes you may get a greater recoil, but it is still a dull thud so most people will be happy with it. It is the best that you can hope for without the additional fine tuning that is necessary to correctly size the piston seal and transfer port.

[Jonas]

Originally Posted by Loki_79 Several people on here have reported that Mr Pope has advised them that the seal does not need re-sizing as it is supposed to be snug. The following is purely my speculation, but I think there are two reasons.


1) Every gun is different. A standard part must seal the largest bore, resulting in a tighter fit on some/most guns.


2) As a measure to reduce the piston bounce without increasing the transfer port diameter. I.e., If you make the piston a perfect fit, you also have to make the transfer port the perfect size - too big and the piston will slam, too small it will bounce. Having a tighter seal increases friction and requires a slightly stronger spring, both of which suppress potential piston bounce and the resulting recoil is the nice dull thud that everyone likes.

re 1) I agree, but the point of buying a V-Glide kit in my opinion is that the parts are already matched to each other. So I would expect the seal to be the "right" fit in the bore, which let me to my initial question.

re 2) I was thinking along these lines too. Tight seal & short stiff spring = dull thud without bounce.
Which I like, only it does sound/feel a little constraint.
I will start by lubricating the seal, currently it's running dry.

[vobster]

The vmach seel in my vmach made longbow was a perfect fit from day one, but then it was fitted by steve after all.
The two seels I've bought for fitting into diy tuned hw97's were damn tight and sapped power. I stopped using them as there was no sign of running in.
The vmach seel in my vglide 97 is a perfect fit (by steve again I presume )


~Anyone spotted the trend yet?