Trigger Mech destruction testing...I need ideas !!

[Iyadiver]

Guys,

There was a post before on trigger mech on big guns.
I too have been curious on how to test these triggers, in actual condition. I want to know, is it safe to load these triggers as per the gun set up I have in mind.

I have come up with 4 trigger mechs which I think is suitable for big guns and they are available from each manufacturer for your own custom work. The info I got from them is available in their website which many of you already knows :


Aimrite / Wong Speargun
Tested to 600# for usage and breaking test of 1250-1750#.
Look at http://www.wongspearguns.com/topten2.html


Kitto / Internet Custom Speargun
There are two models here, the standard 17-4 stainless and the Millenium model which uses Haynes 718 superalloy. Let's take the top model of the Millenium and its information. It has been tested to 1950#. Here I read as tested, not broken at that pressure.
Here I also read that 1950# is equal to 20 of 5/8 bands. So each of 5/8 bands = a bit under 100# of rubber pressure. This info is important to learn of the famous Alexander trigger mech which they also sell. Look at : http://spearguns.netfirms.com/mechanism.html


Steve Alexander
All I have from Kitto website on Alexander trigger mech is that it can handle upto 8 bands or more. So I am assuming 8 x 100# = 800# of trigger pressure as safe, if 5/8" band being the common choice for bluewater guns.


Riffe
There is no information on their website to what kind of testing they have done on their trigger mech. However their #Bluewater gun comes standard with 4 x 5/8 bands. Riffe stated their 5/8" bands give 120# of pressure. So Riffe comfortably applies 480# of pressure on their most powerful models. I personally been applying 6 x 9/16" bands on tyhe MT3 and MT5. 9/16" band of Riffe brand is at 90# according to their 2002 catalog. So 540# has been so far so good in real application. Jay Riffe didn't say a word when I asked him that I want to use 6 x 9/16" bands on the MT3 of MT5.


Of all the triggers mentioned, I have only tried two brands. One is the Riffe and the other is an Alexander from a Collins speargun. The Collins I have is a small reef gun so I never applied more than 300# of pressure. The Riffe trigger is the one I been abusing, thus my concern is more for the Riffe trigger.

I have seen the trigger testing method on that 1000# of pressure Super Tuna gun using Jack Prodo trigger unit.
Look at http://rocknfish.com/Bench_Test.html

I like the test of this 1000# pressure Super Tuna Gun because it uses the entire trigger unit, handle and part of the gun barrel, a very realistic test compared to a test that ONLY place a tigger mech in a special block to house a modular trigger mech and the trigger mech get pulled to a specified pressure.

A speargun needs everything to work together and when one loads a speargun, first the muzzle will get squeezed by the rubber tension. At the other end, the trigger mech gets "pulling" pressure. In between this squeeze of the muzzle and trigger sear being pulled by the shaft, the barrel of the speargun get squeezed. A maximum breaking limit of a trigger mech does not indicate the overall strength of the gun. We must pay a great deal of attention to the strength of the muzzle, the barrel and what material that houses the trigger unit.

The most common bluewater high power spearguns are made of teak and many are laminated teak. My data book from West System ( wood laminating and epoxy resin specialist ) have shown teak and especially laminated teak has great strength. For speargun application 1,000# or even 2000# of pressure is not a big deal. However the worry is not the teak in my opinion, the worry is the amount of teak being removed to create the muzzle to contain the rubbers and the trigger mech. Maybe this is the reason Alexander makes aluminum muzzle even for teak guns. With aluminum muzzle, by design a lot more of the teak wood is being used in compression mode, which is the best strength for any wood, especially laminated ones where the grain of the wood can be arranged in its strongest direction in criss cross fashion.

I would like to see a test where a laminated teak gun of bluewater caliber being tested to 1200# with the trigger mech placed on the teak stock itself, instead of a special test block. I find the 1200# of pull pressure a safe figure because I think the normal extreme use of a Bluewater gun is about 600-700# of rubber pressure. I am no expert but we can tell this figure by knowing the amount of bands and size those famous blue water hunters installed on their guns, the information is easily available on the net or in books.

Continue on next post....................

 

[Iyadiver]

Continue...............

Why suddenly I show interest in testing a trigger mech ?
Yesterday my friend tested his MT5 which already has 6 x 9/16" rubbers, he tested it with 7 x 9/16" rubbers. So a total of 630# at his finger trip. I fired the gun at nothing to feel the recoil. I used two hands, the recoil is more like my Riffe Standard #4 using 3/8" shaft shooting 4 x 5/8" bands ( 480#). His MT5 has the full wing kit and aluminum muzzle option and 3/8" shaft. As far as my hands are concerned and its recoil, if feels OK, thus I want to do more testing on the accuracy of this MT5 using 7 x 9/16" rubbers. The power feels good. I don't want to just email Jay Riffe and ask him, can I use 7 rubbers of 9/16" on that MT5 ? I think he will think I am a nut case. I also want to see and test for myself for my own curiosity and pleasure of testing.

This MT5 has 3 double wraps of shooting line, a coated cable of 500#. The entire shooting line is 9.2 meters ( 30.3 feet ). Considering the 65" shaft length and additional Ice Pick slip tip, less the length of how the shooting line get crimped to the 4th tab and a required penetration of no less than 2 feet for a broadside hit of a tuna and allowance for that Ice Pick to toggle free, I am looking at a gross 10.85 meter maximum shaft travel. Net range is at 10.25 meters ( 33.8 feet ). Judging from the way this 3/8" shaft has a left over energy to un-spin the reel with the brake applied and take away another 3 feet of 1000# Kevlar on top of it already traveling 10.85 meters into the water. I can say that it can be very effective at 10 meters ( 33 feet ).

MT3 with 3 double wraps of 500# coated cable shooting 6 x 9/16 rubbers and breaking 5 of the cable strands due to left over energy when shot at nothing. Now I use 4 double wraps. My last test on a 3 double wraps shooting line attached to a reel and shooting the same 6 rubbers, resulted in the reel in drag mode un-spinning 2 feet of the 1000# Kevlar. I can now roughly relate left over energy of my guns based on reel pay out.

So, in order to safely test an MT5 with 7 x 9/16" rubbers, I must first test the trigger unit and all parts on the MT5 which gets pressure burden under loading. My concern for an MT5 or any Metal Tech series are the aluminum barrel and the plastic material that makes the butt of the gun which also houses the modular trigger module. As for the aluminum muzzle, its thickness is much thicker than the barrel itself so, I have no worry. It will be nice to test it too though.

So me and my friend had a long chat yesterday on the boat after he loaded 7 rubbers on his MT5 for 3 dives and 3 experiment firing in the water. So we have shot 3 times and he has kept the MT cocked for at least a total of 1hr during those 3 dives. So far so good.

My main worry is that most manufacturer test triggers from new units. I want to use a unit that has been worned out by shots, sometimes forceful shaft insertion, have been exposed to sea water immersion and have spent long time in cocked condition. The shaft is another worry. Everytime a speargun is shot, wear and tear will occur, regardless of make. Wear and tear will occur at 2 sears on the Riffe trigger and the shaft sear.

I am looking at a possibly different test method than the one on the Rock n Fish website thus I want ideas from the genius on the board. I am thingking to use my short MT0 as the test gun. It shares all the same part with the MT5, except a much shorter barrel. I know that shorter barrel will yield better rigidty but as far as my understanding as I see visually on how the Riffe Metal Tech series get their barrels squeezed when gun is loaded, longer barrel or shorter barrel will not make much different. I hope I am correct on this assumption.

So what I intend to do is make a dummy muzzle for my MT0 which will act as the part/adaptor which will allow me to install the MT0 in complete form ( less muzzle only ) on a test bench. I will use my worn out 3/8 shaft of the MT0. The test will be conducted at 800# of pressure, to simulate the need to operate at 630# generated by the 7 bands. I will try to shoot at least 20 shots. I will also simulate a long term cocked condition at 800# of no less than 24 hours, to see if anything breaks. The last test will be the destruction testing, I have to load the "gun" to the limit untill something breaks. May it be the barrel, trigger mech or the plastic butt, I can only speculate.

Now the difficulty is applying all this load, which I think at least 1,200# of final pulling pressure must be achieved. At 1,200# I get almost double my requirement, thus it should be safe. When a 3000psi scuba tank is hydrotested, they pressurized it to 5,000 psi. I think I should at least follow that kind of industry standard.

My thoughts on the pressure producing component will be a hydraulic kind of jack, so that repeated shots simulation will not tire me and will be fast to set up. A known diameter of the jack ram rod and with a pressure gauge attached to the pumping fluid, will be able to be translated to pounds/kilogram of push pressure. If anyone has engineering backgrounds on hydraulics, it will be a great help. I can't afford the expensive set up like Wong/Aimrite trigger mech test bench also using haydraulics as seen on their marketing video. I need a simpler unit which I probably can rent.

Of all the components that makes a trigger mech, my number one fear is the pin that holds the sears. Second fear will be the housing that cases the pin and sears. The sears themselves are generally thick but works in friction mode, thus probably only long term test can reveal how long they are expected to last at a given test pressure. The pin does get a bit rubbed in the mechanical action of the sear releasing the shaft but I worry of it breaking at its end, not in the middle rubbed area. Casing relies on its strength of material and thickness. I think in any extreme high pressure test, the pin and the casing meterial will be the first to go.

So any idea to make this test do-able, affordable and safe will be most appreciated.

IYA

 

[Murat]

:hmm

Look at the teak-sea they have gun models with up to 8*16mm bands with high strech distance, and gun weights 16kg....

Ask them if they know any cheap method to test guns...

http://www.teak-sea.com/index_an.html

 

[shaneshac]

Hey Iya, how do the shark fin tabs or notches withstand so much pressure without being ripped off the shaft?

What thickness shaft are you launching with 7 5/8 bands?

Do you have to do a countdown 10,9,8,7...........BOOM!!!!!!!

 

[Murat]

Trigger test bench

The cheapest way i think is nail/secure the trigger to the roof or somewhere else tie ss cable to trigger, collect your pals and hang on the cable rofl :duh

 

[Iyadiver]

Murat,

I like that nail on the roof idea......
That 8 x 16mm gun is way too much for me Murat and 196cm makes me feel like a dwarf. MT5 at 62" / 157cm is already too big for me, I personally like MT3 best.


Shane,

The MT5 we use is with 3/8" shaft. It comes with 4 loading tabs
( 1 extra is special order, 3 is basic ), shark fin type. So I can take 8 bands. Even 3 of 9/16 bands on a single loading tab no problem on the welding, tried many times.

My motto is why have a less powerful gun when you can rig your gun more powerful, as long as it can retain good accuracy and acceptable recoil.

Recoil is something you can live with and tolerate as practice goes by. My test method is simple, if that gun loaded with maximum band and still can be shot with a single hand without the grip coming off my hand..........it is acceptable. Two hands hold are just for faster tracking to me not recoil control. I grew up shooting pneumatics and JBL-s, so I am so used to single hand shot, it not adviseable on a powerful gun but since I can handle it, that already got to be a habit by then.

Accuracy........well I need to test that in detail with 7 bands. It is hard to find 10 meter visibility in close by water, I need to go far, if I go far, I can't stop the urge to hunt.

IYA

 

[icarus pacific]

Hey Iya, nice to hear from you. Next time you take a hike, we need a note... :t

Anyways, I applaud your interest in determining the fatigue point on a used trigger assembly- surley an indication of real world usage, but that is also where the manufacturer has no real contol over- the misuse and maintenance and why most things marine and otherwise need to be designed anfd built to exceed most logical situations. Like six and seven bands... :duh

The thing that really pounds a trigger, and I'm talking about a Riffe, Alexander and JBL, are from slamming the shaft in. The sear that engages the shaft's notch has very little wear in proper use. The ramming of the spearshaft tends to not only dislodge the return spring but more importantly it rounds off the shaft's notch and this is where it gets ugly- that notch in the shaft is cut in such a way as to provide the maximum amount of surface area for the trigger to bear against. When that area is lessened it invites additional wear from the force of the bands now being concentrated on a smaller area. Shafts come with some small relieving of the sharp edges to allow for a smooth release, but if the shaft has a waaay rolled edge from wear and/or misuse, it's a very unsettling matter of time before you shake the gun wrong or drop it and the thing decides to let loose. :blackeye

I've been witness to two shafts doing this, one a JBL and the other a seriously dinged-up Riffe. Both guns let loose while the divers were hanging off, which in itself is buggered up- SCUBA GUYS-guns should always be unloaded before starting your ascent!! and for freedivers- point the damn things down! One of the shafts put a beauty ding in the bow of the Conception in Santa Barbara, the other landed somewhere on Santa Cruz Island. :mute

One other thing that comes to this fertile mind is that as the tension against the trigger sear is increased, the amount of force needed to release that tension increases as well. I'm not sure that it's a linear increase but I wouldn't doubt it. That means if the trigger sear or shaft notch isn't deburred and doesn't have a little bit of roll in the edge, it's gonna take more fingers and bigger arms than I have to set things into motion... so it's more a matter of designing for use than designing for ultimate strength.

I think.

And by the way- those Collins guns are sweet tools, but when he goes off saying that laminated guns are cheaper to make and weaker than solid stock guns, his head's weaker than the most trashed trigger. :hmm

 

[Iyadiver]

Uncle Sven,

Exactly what I need, expertise from seniors like you.
I am sure Jay Riffe will not broadcast his trigger maximum strength due to the possibility of someone taking it for granted and abused it as you explained. I remember he telling me that slamming a big shaft on the trigger unit for insertion is BAD practice.

At 630# the trigger pull is almost no difference than at 300# or so, amazing.

I got an info on the web on how to build a cheap hydraulic ram to use as scale. Either I installed a pressure gauge on a 2ton automotive hydraulic jack or I borrow a propeller removal hydraulic tracker for this test. This won't happen so soon, maybe early next year.

A Filifino I met have friends who have been using 5 x 5/8" bands on their Riffe, that is 600# of pressure, my 7 x 9/16" rubbers is not extreme at 630#.... ...excuses..... he he he.

I am also curious at what pressure will the Riffe trigger starts to feel heavy. I don't think based on up to 630# pressure I applied I can draw any linear graph, maybe at some higher pressure a sharp increase might occur. This is unique engineering.

Let see what happen during the test. I must make a proper platform first before the hydraulic requirement. With a hydraulic jack, all I need is to pump a few strokes to achieve hundreds of pound of equivalent pressure. Sure easier than using springs.

Wish me luck,
IYA