Last week I received a new type of transferportseal but since it was crushed in the mail I had to toss it.
Thought it over and recalled I tried to fit a bolt seal on top last summer.
That didn't work because they were to thick and popped off.
The .177 probe seals I got for my QB78 are thinner and have a larger dia.
The fit is perfect!

Here's how it looks fitted on the tube

After putting it back together I took a few shots and the results were positive.
Since I wanted to shoot a full string I emptied the gun, inserted a new powerlet and left it for half an hour to adapt room temperature.
All shots on all three strings were taken with 60 seconds between shots.
Here's the graph

Here are the strings

If you'd like to try these seals for yourself,
in the USA they can be bought @
http://www.charliedatuna.com (soldas part ofthe QB-78 tune kit only)
in the UK they can be bought @
http://woodfield-gcp.webs.com Such a seal has to be placed un-lubed !!