There are no gasrams for the 1250.
Those that are available for the other Gamos are 12fpe (UK limit)
The only drop-in gasrams that are over 12fpe are for the Kodiak/Patriot and the R1/HW80.
All these gasrams (12fpe as well as the powerful ones) are sealed so the power can not be adjusted.
I hope this info helped.
It's a shame there are no gasrams for the Gamo 1250 / RWS Diana 350 / ... and other guns.