So I made my own on/off today (pics)

[Pneumagger]

very cool

I thought the ULT had such a light pull cause of the smaller head not pin dia, less surface area on the head = less pressure pushing it = lighter pull + less reactivity.

But I could be wrong

Looking forward to some test vids.

In the open state, pressure completely surrounds the head (the pressure has filled the dump chamber too) so the head diameter is not relevent to the free travel trigger pull weight. All of the forces balance out except for the pin diameter going to the sear. Until the dump chamber empties, the head diameter plays no role in weight of pull.

This is why putting a RT on/off in classic mag greatly reduces the trigger pull and the same reason the centerflag on/offs had small diameter pins (less force for the solenoid to pill). Likewise, the ULT's rediculously skinny center post is what gives it that low pull force. I think uses something like a -001 oring.

In the past, all AGD and aftermarket on/offs created the inbalance or change of force by reducing the pull weight (pin diameter) or increasing the on/off top pressure (RT). This would become the first on/off to INCREASE the top diameter to amplify the RT effect.

My assumption as to why this hasn't been done before is either:
a) Field liability involving, more or less, full auto behaving automags
b) The excessive return force will buckle/bend the pin shaft
c) The excessive return force will somehow damage the sear.

Since Vetter pumping 3000 psi to mags (and others routinely putting 1200-1500 into them) my guess is that option b or c are unlikely. Now would I want to feed this on/off 1200+ psi?... probably not. But 800-1000 psi should not subject the pin or sear to forces previously unheard of.

I'm sure Tom/AGD has tinkered with the idea of super reactive on/offs.
Maybe he can shed some light on the subject.

[behemoth]

This may make for a heavier trigger pull. The top of the on off pin has a larger surface area and thus may require more finger pressure to fully push it to the top position. it will undoubtedly be more reactive though. It may be a worthwhile trade off.

I look forward to seeing the test results. As I cant really visualize how this will affect the weight of the pull.

Very cool

Welcome back.

[teufelhunden]

Welcome back.

hahahahahahaha +1 to you sir

[Ando]

Welcome back.

OGRE...

[leloup]

If this works, and price points stay at $50 or less, put me down for one. Very neat ideas. How many other markers can people re-engineer the parts to change operational aspects. Very few, and they are all greats.

[Spider-TW]

As long as we are waiting around for a test, what size o-ring will that be on top?

Another reason it may not have been done before;

The force on the pin pushes the sear up on the bolt lip. To look at the sear, you would think that it was designed to let the lip ride down it. If you just let the sear go and immediately release the trigger, you might be able to catch the bolt coming back and stick it with the extra force.

[Pneumagger]

Don't worry... if it's too reactive I already have an auxillary design that should only give about 1.9X RTP reactivity.
Since it's a bit more difficult to make and the reactivity is lower I deided not to try it first.

I don't think sear wear would be an issue or all the people running 1200+ psi to get more reactivity would see greater wear too.

[Spider-TW]

I doubt it will do any real harm, I was just thinking it could bind. It's an interesting thought that 1200 psi is only a 50% increase in the RT pin force over 800 psi.

I see your numbers there. So, you're looking at about 14+ lbs on a discharged classic? Maybe 20-30+ lbs on an RT? That RT might get uncomfortable, but in a good way.

Do you still have a video camera? I found a copy of the old video "How to build a pneumag" the other day.

[hill160881]

^^^^Edit:Very funny, same lines of thought at the same time^^^^


If my thinking is right it will be very reactive. Im not doing any real math here but if you increase from 800 psi to 1000 psi then that is an increase of 25% not 350% lol.

My thinking may be wrong but increasing the PSI(pounds per square inch) is the same as increasing the surface area(square incheses) that it acts on right? It may just be I am missing something as I have not had my tea yet this morning..

[Spider-TW]

^^^^Edit:Very funny, same lines of thought at the same time^^^^


If my thinking is right it will be very reactive. Im not doing any real math here but if you increase from 800 psi to 1000 psi then that is an increase of 25% not 350% lol.

My thinking may be wrong but increasing the PSI(pounds per square inch) is the same as increasing the surface area(square incheses) that it acts on right? It may just be I am missing something as I have not had my tea yet this morning..

True, but the FAT HEAD on/off has a higher differential at any pressure and the idea is to get that force up without the higher input pressure.

That's my vote. FAT HEAD on/off, or FH for short.

[Pneumagger]

Increasing the pressure with any on off should increse the return force linearly, while incresing the pin head diameter causes a return force increase at a rate proportional to the square of the radial increase. That squared radius term is of primary concern here.

F=PA ... force = pressure X pi X radius^2

Example: Doubling the pressure should ideally double the return force. But doubling the diameter will cause a four-fold increase in return force. There are 4 important variables for an RT mag... 3 variable for a Classic mag. Pin diameter, head diameter, input pressure, and operating pressure.

Lets say operating pressure is about 400psi (although this may vary depending on velocity, temperature, gas used, or valve type). For now input pressure will be 900psi and an RTP pin diameters are about .071 & .120 inches. However, Fat Head diameters are roughly .062 and .183 (I havn't decided on final dimensions/forces yet). We'll have to compare the opposing forces to generate the ideal pull:return ratios... excluding oring & sear friction of course. I'd guess there is about 0.5-1 pound of opposing oring and sear friction in either direction for realistic estimates of return force ratios.

These are all just ideal calculations and estimates for now.

RTP @ 900psi:
(900psi*.120^2/4*pi) = 10.1# return force
(400psi*.031^2/4*pi) = 1.5# pull force
ideal Pull:Return Ratio @ 850psi... 1:6.7
est. realistic ratio @ 900psi... 1:3.6

Fat Head @ 900psi:
(900psi*.183^2/4*pi) = 23.7# return force
(400psi*.062^2/4*pi) = 1.5# pull force
ideal Pull:Return Ratio @ 900psi... 1:19.75
est. realistic ratio @ 900psi... 1:10.3

RTP @ 2100psi:
(2100psi*.120^2/4*pi) = 23.7# return force
(400psi*.071^2/4*pi) = 1.5# pull force
ideal Pull:Return Ratio @ 1600psi... 1:15.8
est. realistic ratio @ 900psi... 1:9.1

Classic (Stock on off):
(400psi*.120^2/4*pi) = 4.5# return force
(400psi*.120^2/4*pi) = 4.5# pull force
ideal Classic Pull:Return Ratio... 1:1
est. realistic ratio... 1:0.7

Classic (with Fat Head):
(400psi*.183^2/4*pi) = 10.5# return force
(400psi*.062^2/4*pi) = 1.2# pull force
ideal FH Classic Pull:Return Ratio... 1:8.8
est. realistic ratio @ 900psi... 1:4.3

Summary: For an RTP on/off to appraoch reactivity ratios of the prototype FH the input would need to be around 2000+psi. I may end up dialing the FH reactivity back a bit... but I'll know more after testing.

Also interesting is the fact that the severely stepped pin should give a CLASSIC VALVE similar force ratios like an RT valve. These are just offhand calculations so i'll believe this when I see it. I'm skeptical but I'll go ahead and test it too. Plus, with only 400psi topside on/off pressure flow will be limited and shootdown would be severe if the trigger were attempted to be bouced.

[hill160881]

I love it.

My reverse mag may as well

[Tropical Life]

This may make for a heavier trigger pull. The top of the on off pin has a larger surface area and thus may require more finger pressure to fully push it to the top position. it will undoubtedly be more reactive though. It may be a worthwhile trade off.

I look forward to seeing the test results. As I cant really visualize how this will affect the weight of the pull.

Very cool

Good to see you back!

[behemoth]

Good to see you back!

Real talk. It was a shame to lose such an asset to the community.

[mobsterboy]

Quit yer yapping and get to testing!