Did someone say pneumatic spearguns
The Mares Sten trigger sear is only adjustable for depth of engagement with the piston flange but unfortunately not for weight of release. Polishing both the trigger sear surface and the piston flange area where it engages may help a bit making a smoother release. Also try changing the oil to 5W fully synthetic motorbike fork oil, which is much more slippery and will increase piston speed down the bore a bit as a bonus. The standard oil Mares fills their guns with seems to have had its origins in a Fiat transmission!
MC FORK OIL 5 (FULL SYNTHETIC) | Penrite Oil
The main problem with the older Stens is the 3mm diameter trigger release push pin and corresponding o-ring.
Under the usual 20 BAR (~290 psi) operating pressure of a pneumatic speargun the o-ring is gripped very tightly. On the Mares Cyrano and later Evo and Sten models the push pin was reduced to 1.5mm diameter for much reduced release effort.
There is a kit available for 16.90 Euro available from Edosub in Italy that will adapt the Sten to the smaller diameter Cyrano pin.
His site is only in Italian (Google Translate is your friend!) but Edo speaks English well and responds to emails quickly. Remind him you are outside the EU so listed prices should be adjusted to be VAT-exempt.
Kit riduzione spillo
This modification kit, for the trigger / retaining pin connection pin, allows to eliminate the 3.0mm diameter pin, standard on many oleopneumatic shotguns, and to replace it with a 1.50mm one.
This modification greatly increases the sensitivity of shot, reducing the force that the finger must apply to the trigger when the piston is released from the retaining tooth.
This kit is compatible with most of the rifles on the market:
-Cresses: SL and Star
-Mares: Reef and old Sten
-Seac: Ace
-Tigullio: Ras
The kit includes 5 pieces:
-1 O-ring for the piston guide bush
-1 piston guide bush
-1 connection piston ø 1.50mm
-1 O-ring for the piston
-1 cup-shaped stainless steel bushing, with screwdriver cut
In addition, replacement O-rings are supplied as standard.
THIS QUICK COUPLING KIT CAN NOT BE ABSOLUTELY MOUNTED ON THE SALVIMAR PREDATHOR, PREDATHOR EMPTY, DARK SIDE, ETC.
If you are ordering from Edosub, it may be a good idea to add a couple of extra items to offset the shipping (which is usually high out of Italy to non-EU countries)
These replacement rubber cups fit the Mares air pumps (not available from Mares, incredibly you have to buy a whole new pump!)
Guarnizione pompa
Seal kits:
Serie guarnizioni
High performance muzzle kit:
Testata Salvi per Sten
General Mares spares:
Ricambi f. pneumatici
Hope this helps!