Bottom Pivoting Trigger Design

I'm designing a test barrel rig for a project that I've been working on and was considering what I would need for a trigger. I don't have a milling machine, so I'm a bit limited on what I can do. I did a bit of a web search on trigger design and looked at all the images on Google Images, but all seemed more complicated than I really needed for this project. I originally wanted to use one of the cheaper electrically operated solenoids, but I just don't think they have enough power to set off a primer.

So, as I got to thinking about the ones that I saw on web, I noticed that all of them basically had a trigger that pivoted from the *top* and then had at least one other piece to change the rotation from how the trigger what was necessary to cock / release the firing pin. There just seemed like there should be a way with less parts. As I thought about it a bit, I came up with the idea of pivoting the trigger from the bottom, not from the top. The trigger gets pulled back, rotating on the bottom of the trigger, which then pulls the firing pin / open bolt back with the top of the trigger. This continues until the catch is not able to maintain contact with the firing pin / open bolt anymore and at this point, the compressed energy of the spring attached to the firing pin / open bolt is released, causing it to go forward and strike the primer.

Something like this:

http://images.spambob.net/navy-vet-1...trigger-01.png

This is just a quick-and-dirty sketch... I show it as an open bolt since it's quicker to draw and for a single shot test barrel device, an open bolt is acceptable. With the dimensions and angles that I have here, it would not retract the open bolt far enough to allow you room to load a new round, but that could be changed by increasing the height of the tab that catches on the bottom of the open bolt and changing the cutout angle at the front of the trigger. I tried a 10 degree angle and that obviously was not enough. I switched it to a 23 degree angle on this drawing and it's still not right, but getting close. But, it's good enough for illustration purposes for the discussion at hand...

Has anyone ever seen a firearm with a bottom pivoting trigger? Surely I'm not the first person to come up with this idea...

the very top point of the green trigger in the upper drawing: it will travel in an arc to where it will drop below the bolt and allow the bolt to move forward

but...

how does it reset?

seems it would have to move back through that arc but the bolt is now forward and blocking some of the arc.

or will you have to manually retract the bolt so the trigger can reset forward?

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Originally Posted by Walter Laich

the very top point of the green trigger in the upper drawing: it will travel in an arc to where it will drop below the bolt and allow the bolt to move forward

but...

how does it reset?

seems it would have to move back through that arc but the bolt is now forward and blocking some of the arc.

or will you have to manually retract the bolt so the trigger can reset forward?

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This is just for a fixed barrel test device, so the bolt would be manually retracted each time. I did not add in the spring that would be necessary on the rear of the trigger to make it return forward either. I suspect that if someone wanted to develop this sort of trigger for a real firearm, the bolt / striker could be modified to address that issue.

So, you've never heard of a bottom pivoting trigger design either?

With a recoil spring to cycle the bolt it is gona make a strong trigger finger. Reset is another issue as posted before.

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Originally Posted by RED333

With a recoil spring to cycle the bolt it is gona make a strong trigger finger. Reset is another issue as posted before.

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Not only that, but with the geometry illustrated, the trigger is going to have to move the bolt backwards against that spring.

Another point is, what is your test barrel testing? If it is the safety of very heavy loads, you might prefer to have your finger somewhere else. A photographic cable or pneumatic release might be adapted.

You can get a very good comparative measure of recoil from the distance a heavy test barrel, suspended horizontally at both ends, moves. Someone with better physics and mathematics than mine could probably extract an absolute, numerical measurement too. The best way is to have a flexible cloth tape measure running through a slot. The recoiling barrel pulls it through, and as it returns to rest it can't stuff it back again. This measure is likely to be upset by a moving bolt.

I once tested the moment of inertia of an elderly and therefore not specially light English best shotgun, against a reasonably good Spanish one of nearly identical weight. I suspended them by the point of balance (which was about identical), and dragged both muzzles down about eight inches with a single loop of thread, running through a little hook screwed into the floor. When I burned through the thread, so as to impart no force, the English gun oscillated far less, and settled down faster. With their accuracy and knowledge of stresses they had got more of the weight into the middle. There is no reason why you shouldn't trigger a test barrel the same way.

With a typical top pivoting trigger, you need an extra part to change the rotation direction of the trigger into an opposite rotation direction of the sear.

http://images.spambob.net/navy-vet-1...trigger-01.png

Because of the rounded contour of the sear and the cutout in the bolt, the bolt would not be additionally depressed against the spring during the trigger pull, so the weight of the trigger pull would just be due to the friction of the sear to the bolt and trigger/sear spring (not shown in this drawing).

Which implies to me that it would be possible to combine the sear with the trigger if you move the top pivot point to the back of the trigger and get something like this:

http://images.spambob.net/navy-vet-1...trigger-02.png

EDITED: I added in the spring that would be necessary to pivot the sear back up.

if this is a test barrel....then why do you need a "trigger" at all?

you could just lock the bolt forward and use something like a pinball machine plunger.

Your original design is a double-action trigger,,one that cocks and then releases the hammer at the end of it's travel.
Nothing wrong with that at all. You will need a spring loaded double action sear in the trigger itself to push out of the way and snap back up into position as the trigger trys to rebounds back into it's position in front of the breech block when it's down.
In the second drawing, you can elliminate the secondary sear by putting the rotation point of the trigger on it's opposite end (left end).
Then the sear engagement tip on the right end to engage the bolt.
...Which is what you have in the third drawing. Just don't make the sear engagement so far away from the pivot. The trigger pull will be very heavy and long. Keep the trigger spur itself as close to the pivot point/in line with it as possible for best leverage.

All will work. Open bolt firing designs are not new. A couple Single Shot 22 rifles in the 60's were open bolt self ejecting (H&R was one I think).
ATF frowns on open bolt semi auto designs for the easy ability to go to the next step to a STEN type design. MArlins Model 50 was one of those and was discontinued back in 1935. Nice rifle if you can find one!

Might want to look at this design for a test rig. One can use a wire or string to get well away from the test with ease.
http://www.pastimesgunsandtackle.com.../prod_2634.jpg

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Originally Posted by NavyVet1959

With a typical top pivoting trigger, you need an extra part to change the rotation direction of the trigger into an opposite rotation direction of the sear.

http://images.spambob.net/navy-vet-1...trigger-01.png

Because of the rounded contour of the sear and the cutout in the bolt, the bolt would not be additionally depressed against the spring during the trigger pull, so the weight of the trigger pull would just be due to the friction of the sear to the bolt and trigger/sear spring (not shown in this drawing).

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And if you modified that to add in the need for the sear spring, you would probably end up with something like this:

http://images.spambob.net/navy-vet-1...trigger-03.png

But at that point, a milling machine would start looking pretty useful. :(

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Originally Posted by NavyVet1959

And if you modified that to add in the need for the sear spring, you would probably end up with something like this:

http://images.spambob.net/navy-vet-1...trigger-03.png

But at that point, a milling machine would start looking pretty useful. :(

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The problem with this design is as long as the trigger is depressed essentialy what you have is a machine gun that fires from an open bolt. At least it looks to me by this drawing there is a need for a disconnect to prevent this from happening.

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Originally Posted by jetinteriorguy

The problem with this design is as long as the trigger is depressed essentialy what you have is a machine gun that fires from an open bolt. At least it looks to me by this drawing there is a need for a disconnect to prevent this from happening.

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I suspect most of the designs would have that problem, but this is for a single shot test barrel (i.e. no magazine), so it's not an issue.

Oops, sorry I forgot that little tidbit of information. It would make for a very simple machine gun.

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Originally Posted by jetinteriorguy

Oops, sorry I forgot that little tidbit of information. It would make for a very simple machine gun.

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Yep... I could fire one round as fast as I want. :)