Feinwerkbau 300s O-ring seal

[Eidem]

I have seen talk about replacing the metal seal on the 300s with an O-ring seal.
Does anybody here have any experience with that?

[little.O]

Hello
I see no reason why not but you may not get the same consistency as you get with a steel ring.You definitely should not see any improvement by fitting an O ring.
All the best ,Owen

[rockdrill]

'bigtoe01' is the man who has done this so he would be best placed to answer.

From his description it doesn't seem to be just a case of direct replacement of the piston ring by an o-ring, rather a full replacement of the nose of the piston from what I can gather.

[Peter Dunkley]

Hi what reason was given for replacing the seal?
At the normal spec these guns are near perfect, I think I read once that they should be serviced every three million pellets! That's not bad.
I would see no advantage at all in any mods if shooting at the specified power ie. 6 ftlb.
If a power increase is needed then I have no experience.

[Eidem]

I believe I read something about it being a tighter seal and therefore giving the effect of a better air cushion.
The reason for it is that after just recently having replaced buffer and breach seal on both my 300s's
They now feel rougher to shoot.

It must be mentioned that I also did a thorough clean and relubed both guns. In addition I polished the end of the springs
I can feel that the mechanism in both guns run more freely than they used to, but the down side is that they slam harder.
This causes the guns to move around when fired and opens up the groups at longer ranges.

Also now they tend to shoot the heavier JSB heavy diablo much more accurately at+30m than the regular JSB diablo.
It used to be the opposite.

I was wondering if it was possible to try an O-ring seal without modifying or in any other way risk damaging the guns
to compare the results

Of course any other tips in how to bring back the smoothness is welcome too!

Cheers

[18 Wheeler]

Hi what reason was given for replacing the seal?
...If a power increase is needed then I have no experience.

Yes Peter, the aim is to effectively increase swept volume and hence power potential by doing away with the lost volume forward of the metal piston ring.
This bigtoe contribution (post #7 >) may be of interest.

I believe I read something about it being a tighter seal and therefore giving the effect of a better air cushion...

...I was wondering if it was possible to try an O-ring seal without modifying or in any other way risk damaging the guns
to compare the results

Of course any other tips in how to bring back the smoothness is welcome too!

It isn't a straight swap. Correctly fitted metal piston rings should give an effective seal. My FWB 150 piston could not be pushed by hand down the cylinder if the transfer port was blocked, with sustained pressure it would gradually move but over the short duration of a normal shot cycle the seal was perfect.

-I'd start by checking that the conical "transfer port" seal is correctly seated and sealing properly with no debris present. If not then the rifle could become slammy. It should be compressed slightly as you return the cocking lever to the closed position, you can feel this slight resistance. You can try firing with a piece of tissue paper over the breech area to show any obvious leaks, you'll need to restrain the recoil mechanism of course.

-Then check that the sledge is moving correctly during firing.

-If that is all good then take it apart and check that the piston seal is doing its job as outlined above. With care you can see how closely the ends of the piston ring are when it is just entering the compression tube.

[Eidem]

Cheers for the link, I had not spotted that post.

I guess the O-ring theory is out then, A little more juice would of course be nice, but not was not the goal. I feel that I have gotten a fair bit more power due to the clean up
and relube. Also I believe that flattening and polishing the ends of the spring have gotten rid of most of the spring twang.
I also consider using a piece of tube with some valve polishing paste to flatten and polish the seat of the piston and the seat on the other side to see if that would improve that
even further?

1. The paper bit. Are you talking about loading the gun putting in a pellet and firing. As of then a leak would show up as an "mark" on the paper around the outside of the seal?
There is a bit of resistance when I close the port, much more than before replacing the seal and buffer on one of the guns, some more than on the other gun. On one of the two
some more than the other.

One of the guns got what I thought to be a little to much resistance. I dis-assembled the gun and saw that the buffer had not seated properly. I heated the buffer and managed
to get it out without damaging it, I noticed that some of the buffer had broken off when pressing in and was stopping the buffer from completely entering.

After fixing this the breach closed more easily.

The new buffers are harder than the old ones, can buffers be a potential cause for the harshness, could it help to remove some material on them?

2. The sledges works properly. That said: From my FWB 80 I have noticed a fair bit of difference in the smoothness depending on which lube I use, but earlier experiments did not give
me as clear differences on the 300s. Maybe this has changed with the internals having been cleaned out properly and now moving freely?
Unfortunately I can not remember what lube I ended up using on the FWB 80....

3. I have been concerned about the metal seal as I did not replace them, I did put a little LT2 under the seals, just a tiny bit to help seal against the piston, not enough for it to bleed out.
My main concern was that I might have been a bit careless when putting the pistons back in. I feel that I should have used a piece of a beer or soda can to protect the edges while
pushing it in, similar to how I would compress the piston springs on a car engine piston when putting it into the engine block. I still believe I was careful pressing them in, but....

But I will have to wait getting new seals as the dealer only has one in stock and I need two new ones. I figured I would try everything else that might improve handling while waiting for
that and maybe learn a thing or two in the process.

[little.O]

Hello again,
Where were you getting the new seals from? I have heard that there are some on the market that are made from a different type of meaterial and because they are not seating correctly the guns were really fast and slammy.
On the subject of lubrication,the springs should be clean and free from any grease.The whole gun only requires about eight drops of light machine
oil in total.If you use any grease on the spring or piston it slows down the action in an inconsistent manner.These rifles were designed and tuned to
produce about 6ftlbs energy and be very accurate with light flat nosed pellets at 10 mtrs and not for any other purpose.Over powering them can cause camage to the sledge and its action will not be as effective.If you wanted more power it would be necessary to find some way to damp down the sledge to so stop it coming to the end of its travel and causing it to move the point of aim.Even the damping may cause it to move!
Hope this helps ,all the best,
Owen.

[Eidem]

I was under the impression that the spring was to be greased, lightly that is and that the cylinder was supposed to be clean?

Any other got views on this?

I will try to clean out the gun I have here and compare it to the other one.

I have bought my parts at:
http://www./itm/330793536690?var=540083252855&ssPageName=STRK:MESI NDXX:IT&_trksid=p3984.m1436.l2649

Always gotten good service, fast and cheap

Do not really need any more power than original. It would be nice, but not at the cost of accuracy.
They where doing app 5mm 5 shot groups at 45m before, both of them.
More than good enough for me

[Eidem]

The green seals and buffer is quite hard.

But Wonky once replied:

"The 300s breech seal & piston buffer have never been made of rubber, they have always been made from urethane.
There is a perceived difference in hardness from the early white/yellow & blue items to the recent green ones but no
difference in the final performance of the rifle when fitted."

So I accepted that.

[rockdrill]

If you wanted more power it would be necessary to find some way to damp down the sledge to so stop it coming to the end of its travel and causing it to move the point of aim.

Just as a point of interest I have had several FWB300's and tinkered with them. Even running a slightly more powerful spring that got the velocity up around 700fps, the sledge mechanism never used the entirety of its available travel.

[Eidem]

My FWB 150 piston could not be pushed by hand down the cylinder if the transfer port was blocked, with sustained pressure it would gradually move but over the short duration of a normal shot cycle the seal was perfect.

Just cleaned out everything properly, can't test it yet but will compare soon.

But the seal did not seal 100% I could push it down, very slowly that is. There is an
fair amount of resistance there. I was under impression that one could not expect
a 100% seal from these seals?

[bigtoe01]

I used an O ring on my piston as i had machined the nose back to remove meat right to the back edge of the piston ring groove. So it was either machine for a new piston ring or machine for an O ring (which is easier) so I chose the O ring.

If you shop around there is a total seal piston ring for higher power output available from Germany...never tried one so I can not comment, but it may be worth a look.

For lube try mixing Slick50 and moly powder, then coat the piston with this VERY thinly, once the lube settles it proved very consistent for me on my 300s