The effects of tophats in spring guns

[UCChris]

Hey all. Got off school yesterday so I decided to tear down a Daisy 1000 I've had laying the garage ever since I can remember.

I got it all torn down and it looks exactly like the rifle in this document.

http://webpages.charter.net/rs_enterprises/guns/RSE%20-%20Daisy%20tear-down%20guide.pdf

My plan is to put a Merlin XL spring and Gamo Tesla seal in it, however, I want to make it a very docile shooter. I'm looking for around 800 fps with 7.9 grain pellets. I'm wondering what would happen if I didn't use the tophat that is in there, instead just using a polished washer. My reasoning is that the tophat adds around 1/2" of preload to the spring.

What I don't know is how the weight of the tophat effects the shot cycle, velocity, etc. The piece is quite heavy for its size. I can get an exact weight measurement for you guys if you want to know.

[Jeff Marshall]

Christopher, I have heard it claimed that a tophat is the only difference between the 1000 and the 800 model, but I cannot personally confirm that.

[Motorhead]

Tophats addressed as to WEIGHT .... heavier they are greater the momentum piston has to NOT BOUNCE back when under the compression stroke.  LIGHTER the tophat Faster shot cycle becomes and easier forward motion of piston will be slowed compressing air.
* Get piston too light and pellet too heavy a REBOUND can happen.

Typical is HEAVIER piston weight for heavier pellets and visa versa.

Tophats Also used as a miens to add pre-load to the spring.

[UCChris]

So if I'm using a light spring (Merlin XL) and mid weight pellet (8.44 grains) would it be best to keep the tophat in or could I get a quicker, gentler shot cycle from forgoing it?

[Motorhead]

So if I'm using a light spring (Merlin XL) and mid weight pellet (8.44 grains) would it be best to keep the tophat in or could I get a quicker, gentler shot cycle from forgoing it?

Have to test it with a lighter hat ... if shot cycle stays smooth and no secondary vibration gets noted your likely good to go.

[rsterne]

So in simple terms, heavier tophats for heavier pellets?....

Bob

[Scotchmo]

So in simple terms, heavier tophats for heavier pellets?....

Bob

Generally, yes.

Piston "bounce" can be tamed with heavier a piston, or a lighter pellet.

If you are getting piston "bounce", lighter pellets can help. Or a heavier tophat/piston.

If you are getting piston "slam", heavier pellets can help. Or a lighter tophat/piston.

The heavier piston/tophat increases the dwell near maximum chamber pressure and gives the slower/heavier pellet time to get moving.

But I find a little bounce gives a better shot cycle than a little too much slam. So I tend to err on the light side for piston/tophat. A little bounce at sea level will also allow a springer to shoot at greater pressure variation (higher altitude).

UCChris,

I would initially set it up like you stated. Minimum tophat/piston mass and minimum preload on a full length spring that has been preset. That will give the smoothest cycle and longest lasting, lowest stress. And then see how it feels/performs with your pellet of choice.