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Old 02-11-2020, 05:56 PM   #46
popgun pete
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Re: Rob Allen Tests Stainless Trigger Mechs

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Originally Posted by Behslayer View Post
Hi Rob,

If you are correct, then every Stainless mech out there with more than one band on it would have the same issue and the trigger pull would increase quickly until the trigger was impossible to pull like it did in your test. Which is not the case.
I am pretty sure that it is their long sear lever tails, double the length of the tail and you halve the pressure at the contact with the trigger retention step. That in turn requires a long or deep trigger mechanism cassette or sear box to provide the pivot pin locations at a wider spacing. Note that in the case of a multi-lever trigger mechanism the very high contact pressure at the sear lever tooth holding onto the shaft tail is progressively reduced at the actual trigger, but there is a lot of load on the pivot pins trying to push the cassette walls apart longitudinally.
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Old 02-13-2020, 01:50 AM   #47
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Re: Rob Allen Tests Stainless Trigger Mechs

Hi Jon,

Please read this

https://www.bssa.org.uk/topics.php?article=11

Reading that makes me even more resistant to using s/s as a trigger.

In our case, it does not work with our geometry. Yes, changing the geometry to lower the loads by extending the trailing arm of the sear will improve things, this is exactly what Pete says, I agree 100%



For us to do that we may as well make a whole new handle. Why do that if this one works fine as is with the composite trigger we use? This test was to show how a s/s trigger performs in our handle.

Regarding testing other brands, we would never show this without the consent of the manufacturer.

I did not say it’s not the geometry, I said with our geometry this is what happens.

Regarding hole positions, the s/s trigger hole is in the same position with the same fit, no deviation. If I over lay the triggers the parts are the same profile where they mesh.

No, our sears are made locally, not in China.
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Old 02-13-2020, 04:18 PM   #48
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Re: Rob Allen Tests Stainless Trigger Mechs

Hi Rob, thanks for the explanation and agreeing that in this case "It is not just the Materials. It is also the Geometry."

Thanks for the link. I've read many many studies on Galling.

Ofcourse Full Stainless Mechs using quality materials, proper manufacturing, and fitting geometry, can function well and not bind to the point of a #15 trigger pull using 2 bands after less than 200 shots. Your results indicate something being off.. either quality of materials, manufacturing, geometry, or design.

The Geometry plays a very important role. The quality of Materials and manufacturing method also play an important role. Not all Stainless is the same. Many of those mechs which have stood the test of time use 17-4PH Stainless Sears. It was a little muddled about exactly what Sears were shown in your test, but I think we can agree that while you do cut your own stainless sears in house with EDM, assumingly from the best quality steel you can source, it seems like the sears shown in the actual test were made somewhere else and sold as aftermarket "upgrades" As such you are not sure of the Steel used, or the manufacturing method. And, I would argue as such there could also be some subtle differences in geometry/positioning.

Stainless Mechs are made specifically to consider galling. Composite Sears and Stainless Sears are not always interchangeable. The materials have different properties and strengths. With some changes in the geometry ie length of lever, and mating of the sears, and upgrading the quality of the Steel to something harder either using 17-4PH or an Alloy, increasing the thickness of the Shaft Sear to match the Trigger Sear, I'm sure it would work fine as an all stainless mech using light loads like 2 bands.

Glad we were able to get to the bottom of this.

One other question. Rob, we have seen the issue of galling/scratching between the Trigger and Shaft Sears in your video and pictures. Do you have any issues with the Carbon Steel Shaft Tang/304 Shaft Sear? Does that area get all scratched up, banged up, deformed?
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Old 02-13-2020, 05:58 PM   #49
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Re: Rob Allen Tests Stainless Trigger Mechs

When you think about it spearguns are the most powerful weapons that run all the propulsive force through their trigger mechanism, nothing else comes close. Say you have a six band gun with 100 pound pull on each band that is 600 pounds being held by a contact area of 1/4" wide and 5/32" deep at most and thus a contact pressure of 15,360 pounds per square inch! Some cannons have had even bigger loads than that using up to (gulp) 10 bands. To keep it simple I am not allowing for the curved bottom of the shaft tail.

Shaft tails are usually 5/16" diameter and are cut to half their depth for the shaft tail notch, mechanism levers being up to 1/4" in thickness, which is what you have on the M8 (actually measured at 0.242").
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Old 02-14-2020, 05:03 PM   #50
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Re: Rob Allen Tests Stainless Trigger Mechs

The Rob Allen “Vecta” trigger mechanism (tested with a non-standard metal trigger) appears to have about 5 to 1 gearing in the sear lever, therefore for a 120 kg loading on the mechanism’s sear tooth the sear lever tail will be directing a force of 24 kg (120/5) at the trigger pivot pin, or slightly forwards of it. Where you actually pull on the plastic trigger is about 1.33 times the radial distance from the trigger retention step to the trigger pivot pin and that gives a mechanical advantage in overcoming the frictional loading on the trigger retention step along with the friction of the trigger pivot pin itself and any residual torque arising from that 24 kg acting around the trigger pivot pin, the radius being very small as the vector passes by just in front of the trigger pivot axis. Testing (with the plastic trigger) shows the trigger pull is 2.4 kg, so the force reduction is by a factor of 50 (120/2.4). If we ignore friction for the moments there is a big mechanical advantage at the trigger finger pull distance compared with the radial offset of the sear lever tail force vector passing by the trigger pivot pin, I estimate it at about 14 times that distance or a factor of 0.0714. 24 kg times 0.0714 equals 1.7 kg and that means friction adds another 0.7 kg to get the trigger pull result of 2.4 kg. The numbers are not exact because the distances are estimated from a photo, but you can see how it works.

Another plastic trigger is the reverse Abellan version which we have looked at before.
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Old 02-15-2020, 03:01 AM   #51
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Re: Rob Allen Tests Stainless Trigger Mechs

Hi Jon,


There is no galling from the spear on the sear notch. This is probably because the spear steel is much harder than the sear steel and, the spear in my opinion does not drag over the sear. It is held fixed in place until the trigger releases the sear. The sear then drops away with very little load on it from the spear. After 17000 cycles there is no sign of wear on either the spear or the top of the sear, other than a slight shine.


Hi Pete,


Your measurements from the picture are very accurate, great calculation. The piston pushing down on the trigger pushes roughly in the muddle of the finger pad, pretty much where a trigger finger would sit. A longer trigger would lower the force required to pull, but this would drop the hand location, increasing muzzle kick. The finger position is set at what we feel is average in terms of comfort. There are obviously some who would prefer the trigger pad to be in a slightly different position. If forward, this would reduce the space for the trigger finger. In cold water with a thick glove the finger will barely fit.
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Old 02-16-2020, 05:09 AM   #52
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Re: Rob Allen Tests Stainless Trigger Mechs

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Originally Posted by popgun pete View Post
The Rob Allen “Vecta” trigger mechanism (tested with a non-standard metal trigger) appears to have about 5 to 1 gearing in the sear lever, therefore for a 120 kg loading on the mechanism’s sear tooth the sear lever tail will be directing a force of 24 kg (120/5) at the trigger pivot pin, or slightly forwards of it. Where you actually pull on the plastic trigger is about 1.33 times the radial distance from the trigger retention step to the trigger pivot pin and that gives a mechanical advantage in overcoming the frictional loading on the trigger retention step along with the friction of the trigger pivot pin itself and any residual torque arising from that 24 kg acting around the trigger pivot pin, the radius being very small as the vector passes by just in front of the trigger pivot axis. Testing (with the plastic trigger) shows the trigger pull is 2.4 kg, so the force reduction is by a factor of 50 (120/2.4). If we ignore friction for the moments there is a big mechanical advantage at the trigger finger pull distance compared with the radial offset of the sear lever tail force vector passing by the trigger pivot pin, I estimate it at about 14 times that distance or a factor of 0.0714. 24 kg times 0.0714 equals 1.7 kg and that means friction adds another 0.7 kg to get the trigger pull result of 2.4 kg. The numbers are not exact because the distances are estimated from a photo, but you can see how it works.

Another plastic trigger is the reverse Abellan version which we have looked at before.

There are 2 versions of this Abellan Trigger. The older version is actually much better than the new version. The difference with the new version is that the internal space has been made much wider to allow for more space for mono in the mech. Wider means that the load has to bridge a larger space and thus the loading profile changes. Since the box walls are only 1.5mm … this causes a problem if the gun is loaded with more than 2 bands and can actually deform the box and cause a misfire. I am not sure if they have now moved back to the older trigger or are still using the wider trigger … but that is one thing to note if you plan on loading up this trigger. Another issue I have with this trigger is the spring for the trigger sear … it is very weak and after time it has a hard time actually resetting the trigger sear. So you need to make sure it is properly maintained and lubricated to allow for good slick action. I think making this spring a little stronger would be a big improvement. Another thing I don't like is the line release … it is set in a position where it is prone to getting bent because it is very exposed and is made of very thin metal. One thing has to be said though … the plastic trigger sear has a very nice predictable trigger pull and it is a very nice solution to the galling problem of SS triggers.
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Old 02-16-2020, 05:52 PM   #53
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Re: Rob Allen Tests Stainless Trigger Mechs

Pete, once again it is so cool that you share your understandings with the rest of us.

Rob, that's amazing to me that after 17,000 cycles you wouldn't have any deformation of a stainless sear. Some divers are like gorillas when they slam the shafts into a gun. It's one of the most common things I see when I take various mechs apart. Even in the picture you post here we can see deformation after just 200 cycles, and dang.... I've seen so many trigger sears deformed using Carbon steel shafts. I think mostly the issue is Gorilla placement. There are so many divers out there who actually believe you are supposed to slam a shaft into place..

Majd, There's something to be said for a Moulded Stainless Housing which can be fit to the requirements of Sears. They don't cost that much to make. They are extremely strong, and exact. I've become a big fan of Torsion Springs. One of the most common issues I see when taking apart my friends guns because they are having problems are issues with traditional springs. Either they are pulled out of alignment or stretched etc. Whether Torsion or Standard spring, it's very important for the Spring to be Way overbuilt for the task to assure longevity and Gorilla resistance...

One thing is for sure. We could all learn about triggers from Pete and Majd.
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Old 02-16-2020, 06:25 PM   #54
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Re: Rob Allen Tests Stainless Trigger Mechs

Slamming a shaft tail to latch it should not be necessary if the trigger mechanism is properly designed. A problem with dipping sear tooth trigger mechanisms is there is no backing projection on the sear lever, instead the spear tail rams a bulkhead often made of plastic in molded housings which can be snapped off by the impact. In multi-lever trigger mechanisms there is more friction with extra springs to overcome on relatching, so these are best loaded by firmly pressing the shaft into the gun. A loading handle, such as those used with muzzle loading pneumatic guns, can assist in this process by slipping it over the tip and pushing. This works best with closed muzzle guns, but if you grab the gun behind the muzzle with your fingers curled over the shaft you can also use it on open muzzle guns, the loader is carried by an elastic cord on your wrist. As I always have a back-up pneumatic I wear a loader on every dive, unless I am using a polespear.

A loader can be made from a thick wall alloy tube as shown, the center hole goes over the spear tip.

I should add that double flopper shafts with both floppers open on the same pivot pin can be used as a loading handle if you are wearing gloves, but not on a pneumatic!
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