Ermes-Sub Double Roller Trigger Mechanism

  • I have been putting off bashing the pivot pins out of the Ermes-Sub Double Roller mech that I purchased about 9 months ago and only just retrieved it from the spare parts box which I had tossed it into after giving it a quick once over when it first arrived. Now if you remove the rear countersunk socket head screw that forms the pivot pin for the line release lever and which has a biasing torsion spring wrapped around it and a nyloc nut on the inside then you will find that the sear lever swings right out because the only thing stopping that happening was the nyloc nut fouling on the rear step formed in the back of the sear lever. With the sear lever swung through 180 degrees you can pretty well see everything, so really no need to hammer the pivot pins out. The roller sear tooth has a rolled steel split drive pin forced through it and that pin has about 2 mm fore-aft free play in the small vertical side slots in the housing walls. That drive pin is only there to stop the roller falling out and keeping it in the correct lateral orientation in the sear box. The answer to the mystery as to why a square cut spear tail notch will roll this mech is the curved sub-circle cut-out in the sear arm as any fore-aft force acting through there has a downward component as the curved face is in a sense angled. My guess much earlier based on a modified non-roller diagram is pretty much what the mechanism looks like inside except that the backing projection is located a bit further forward than I had thought it was. The backing projection serves to block the line release arm from moving until the sear lever falls and rotates it out of the way. The sear lever has no biasing spring, so if you hold the mech upside down then it will not "dry fire" as it needs gravity to drop if there is no band load on the spear.

    Ermes Sub DR 1R.jpg
    Ermes Sub DR 2R.jpg
    Ermes Sub DR 3R.jpg
    Ermes Sub DR 4R.jpg
    Ermes Sub DR 5R.jpg

    Note the two nylon washers that flank the sear lever and are mounted on the peened over sear lever pivot pin. The ends of the pivot pins are peened over to prevent you pulling the mechanism apart, although a determined whack with a big center punch and hammer would soon knock them out if you really needed them removed. The split drive pins can be easily removed with a small punch such as the one passing through the roller tooth. The front roller on the nose of the sear lever has a fat axle and not much roller, which is good.

  • This annotated photo indicates the terminology being used.

    Ermes Sub DR annotated.jpg

    This trigger mechanism, like many of this type, is not a cam lock mechanism, but a frame lock mechanism. The sear lever under load tries to revolve the trigger which turns against the cross bar just forward of the trigger pivot pin and immobilises it. The cross bar is another tubular split drive pin.

    The trigger mechanism is designed for eurogun shafts with the curved spear tail retention notch which is more or less universal with a flat top for the length that pushes back into the sear box and slightly forwards of there. The mechanism could also be used with square cut spear tail retention notches provided that the shafts also have a flat top, although the determining factor is the nip between the top of the tooth and the ceiling of the sear box roof. This could be adjusted with a different sized roller tooth, however it would need a matching cut-out in the sear lever arm to cup the roller and keep the central "rolling pin handles" drive pin off the slide slots in the housing when the gun is cocked. If they are pulled tight onto the side slots then they could hold the roller up while the sear lever fell away beneath it. That would not happen with a eurogun shaft as the angled face in the spear tail retention notch, actually a curve, will drive the roller downwards.

  • Ermes Sub have managed to squeeze a safety into their trigger mechanism as can be seen here. It is an option, but personally I think that it should be fitted as standard. Up to you to fit it or not, but could be insurance against legal action if the worst occurs from the manufacturer’s perspective.

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