Adjust trigger pull/Mares Sten pneumatic

[WhalerDiver]

Hello Board! I have a Mares Medi Sten pneumatic spear gun. The trigger is SO HARD to pull, it makes it very hard to maintain aim. The manual says to absolutely not adjust the trigger yourself, but I'd like to know if its possible. I also know that if I send it to Mares to do the work, I won't see my gun again for at least 2 months. Thanks!

 

[Fibonacci]

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!

 

[WhalerDiver]

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!

Hello Fibonacci! Thank you so much for the quick reply!

I was able to (finally) reach a Mares tech about the trigger release, and he told me what to do: there is a tiny screw, barely visible through a hole in the plastic handle, just behind the trigger. One half turn of the screw in a counter clockwise direction, and the trigger is WAAAAY easier to pull. Problem solved!

 

[Fibonacci]

Hello Fibonacci! Thank you so much for the quick reply!

I was able to (finally) reach a Mares tech about the trigger release, and he told me what to do: there is a tiny screw, barely visible through a hole in the plastic handle, just behind the trigger. One half turn of the screw in a counter clockwise direction, and the trigger is WAAAAY easier to pull. Problem solved!

Glad it worked out OK... the adjustment screw increases or decreases the amount of engagement between the sear or Catch Hook (#50 431-63377) and the metal flange at the end of the piston.
Less engagement = less travel or 'creep', less friction and lower perceived weight of pull.
Normally it should be set at 4mm protrusion.