I have a Diana 52 bought in Germany in F-version meaning it orginally sent .177 diabolos at max 175 m/s or 583 fps. I have upgraded it years ago to 900 fps level and upgraded it to a 52 full power factory spring this week so I am looking at 1000 fps or so, at least in theory.

When dismantled I noticed the breech seal had some kind of metal insert and small hole, maybe 2-2,5mm. The replacement seal has around 4,2mm hole. I read somewhere that this metal insert with a small hole might be a reducer shim for the lower power models.

Now that I have the high power spring should I remove the reducer and if so then how ? Do I need to adjust the side lever system if I remove the reducer ?

Will there be problems if I leave the reducer shim in place as the seal itself is in good condition ?

I changed the earlier spring back because my chrono said it gave 20m/s more speed to any bullet than the new spring I got from Germany. This time I also removed the reducer from the air chamber.

The breach seal is a normal Diana 52 seal but between it and the air chamber was a small metal disc sandwiched.

Thickness: 0,23 mm
Diameter: about 10,8mm
Hole diameter 2,20-2,25mm

I put the gun back together with a new breach seal and it seems the power increased a little but I have no access to a chrono at the moment so can not really prove it. I have earlier chrono data with the reducer in place so can at some point measure it´s effect as the rest of the 52 is intact (same spring etc.)