Cheap and easy way to convert triggers from single stage to 2-stage

[nervoustrigger]

First off, this isn't anything new or novel.  The modification has been published many times.  The basic idea is to replace the (or add an) overtravel screw with a spring plunger.  When adjusted properly, you will encounter increased resistance just before the trigger breaks which makes it very predictable. 

The reason I'm posting this is simply because I recently found a cheap source for the spring plungers on Amazon.  The ones on McMaster or Zoro tend to be around $5 each plus shipping cost.  Contrast that with this pack of 10 for $5 with free shipping:
  M4x10mm ball plunger, pkg 10

They look like this:


For these particular ones, I measured 0.027" of travel and right at one pound of initial force.  So if you have a trigger that is prone to sear drag, these may not work well.  Similarly, if you have a heavy trigger, the plunger may not add enough resistance to make the second stage easy to recognize.

Now for an easy example, a Crosman 2400KT.  The factory overtravel screw is an #8-32 which is very similar to M4.  I practiced on a scrap piece and determined that I could chase an #8-32 thread with an M4x0.7 tap and it would have sufficient strength.  Once adjusted, a little threadlocker keeeps it in place:


It worked great so I wanted to go ahead and try it on a QB.  First, out comes the original overtravel screw:


Then off to the shop to drill and tap:


And here it is installed.


Final thoughts...a gun with a predictable trigger break is easier to shoot well.  This mod is cheap and easy and it works.  However the QB would benefit from a higher initial force.  The proximity of the plunger to the trigger's pivot point gives a lot of leverage compared to having it out at the end of the trigger so the second stage isn't as pronounced as it is on the Crosman.  It works well enough but I may swap it out later for a stiffer one.

That's it!  Let me know what you think, and share your experience if you've done something similar.

[Chako]

Thanks for the share , I had no idea about those special screws. Looks as if they were designed for this use

[39M]

Interesting, as I prefer a crisp single stage, or set trigger, that breaks like glass with little to no overtravel.

[Artie]

I did it on a QB and or Disco @ one year ago. Works fine for a "faux" two stage. It let's you know where you are in the squeeze cycle for an over-long trigger travel. I used them to replace/modify existing adjustment screws. For over-travel I use whatever small screw is available and tap/thread cw to a preferred setting, usually just beyond sear release.

[Geronimo]

Thanks for the link, now to get some ordered.

[nervoustrigger]

Just a quick update after some trigger time.

I absolutely love it on the QB.  I ended up replacing the trigger spring with a lighter one and that gives better contrast between the first and second stages:


I made a simple spring guide for it using a flathead screw since it looked like it might be possible for it to bend and slip off the back of the trigger blade.  Together the lighter spring and the spring plunger make for a light pull and a very predictable break.  I wish I had done it sooner.  With that said, it's almost too light for my tastes so I decided to go ahead and put a bag of M5 plungers on order.

No force spec is given so it's a $10 gamble that they are noticeably stiffer than the 1 lb. I measured with the M4.  When they come in, I'll report back on how they measure.

[Bentong]

Thanks for the share, ordered some on the 16th and should get it sometime end of next month.

[nervoustrigger]

Only a 6 week wait, huh?  Why are you so special that you get expedited service  

Actually I ordered mine on Apr 3 and received them on the 13th so it wasn't nearly as long of a wait as predicted by Amazon.  Hopefully that will be true for you as well. 

[Bentong]

Lucky me...actually shipped the following day but must have been loaded to a sailboat from China!

[Gipper]

Take a look at McMaster Carr.  They offer these in several different thread sizes, lengths and spring tensions and ship fast.

https://www.mcmaster.com/#standard-spring-plungers/=17dmoau

Brian

[nervoustrigger]

Take a look at McMaster Carr.  They offer these in several different thread sizes, lengths and spring tensions and ship fast.

Thanks, yeah McMaster has a good selection and I do buy hardware from them on occasion.  However, I don't have a target force in mind and a single one like this https://www.mcmaster.com/#2191a26/=17dnxd5 is $5 plus $5 shipping so I figured I might as well get a small bag of them from Amazon.  That way I'll have several that I can try in different applications and see what works and what doesn't.

[nervoustrigger]

...I decided to go ahead and put a bag of M5 plungers on order.

No force spec is given so it's a $10 gamble that they are noticeably stiffer than the 1 lb. I measured with the M4.  When they come in, I'll report back on how they measure.

The M5 plungers came in today and the initial force measures 28oz.  I think that will be a better choice for the QB given the amount of leverage but it may be a while before I try it out.

Also, the ball has 0.026" of travel.

[rsterne]

Yep, I've done that on a few QB triggers.... along with a softer trigger spring....  It works very well....

Bob

[Geoff]

thank you for the link

[Model25]

On the QB, I made up an adjustable plunger set up that threads into the existing trigger spring hole. Changed the trigger spring to a tension spring located forward of the trigger. I found that it’s much easier to set it up in the lower-less leveraged trigger spring hole, with the added bonus of being able to keep the original over travel adjustment screw. My second stage is adjustable to add from 2 to 14 ounces. The only hard part is finding a small stiff spring. The flint spring on a disposable butane lighter works well here.
Have fun with it, Mike

[nervoustrigger]

I wanted to give you guys a heads up that I did some chrony testing with the 2400KT yesterday evening and the plungers do not work properly because of sear drag.  It should work nicely with one of the drop sear trigger groups, just not with the basic trigger group of models like the 13xx, 2240, 2400, etc.
 
It works great with the QB trigger.

I wish I could still edit the original post in the interest of the readership...hint, hint.

[imadunatic]

I wish I could still edit the original post in the interest of the readership...hint, hint.

What happened with that? It seemed as though I suddenly couldn't edit some of my posts, figured it was just me.... 

[Austringer]

So Jason, exactly what spring plunger worked best with the QB trigger group?

Troy

[Bentong]

I got mine earlier than projected date from amazon....got it on my 78 &79 then did it on my maximus but had to fashion a weaker spring to make the 2nd stage more pronounced. Thanks Jason for the source.

[nervoustrigger]

Hi Troy, I have not installed one of the M5 plungers yet but I think the higher initial force will be a better match.  Using the M4, the wall at the second stage is pretty subtle even after I replaced the trigger spring with a weaker one.  When I do switch over, I will reply back with my thoughts.

Kevin, I think the edit feature becomes disabled 30 minutes after posting, thanks to people getting their feeling hurt and going back and deleting their posts.  Unfortunately, it means the rest of us can't make useful edits that would be better placed in an original post.  I find this particularly problematic for things like tutorials and safety notices.

Bentong, thanks for the update.  I'm glad the mod worked out.