Trigger Mechanism?

[Peter Venkman]

Is there any resource that explains in simpleton language and pictures how the HK trigger mechanism works. Please don't tell me to take it apart and find out for myself; I'm not good with that type of thing. But I would like to know the parts and how they work together to better understand how the mechanism works. I would like to know how the match trigger differs from the standard trigger and what a smith does to the standard trigger to improve it.
Any good books or tutorials on this?

[SIGtrarian]

Have you checked out the stickys at the top of the forum?

http://hkpro.com/forum/showthread.php?t=41104

[Peter Venkman]

Have you checked out the stickys at the top of the forum?

http://hkpro.com/forum/showthread.php?t=41104

Yes, I've been able to locate instructions for how to take it apart (not that I trust myself to do that).

What I would like to know is how it all works. What makes a match trigger different from a standard trigger. Why does the match trigger break so much cleaner than the standard. Why does the standard trigger have so much creep before breaking. What does a smith do to improve a standard trigger. Why not put a match trigger in all USPs. ETC.

[AviatorDave]

There are several characteristics of standard triggers that are different in match or other custom triggers.

First is the pre-travel. This is the distance you pull back on the trigger before it makes contact with, and starts disengaging the sear from the hammer notch.

Then is when you may experience creep, after the sear starts to move. The contact surfaces between the sear and the hammer are normally ground surfaces, but may also be made by other methods of machining. But the sear must be moved some distance before it is completely clear of the hammer and it is allowed to fly forward under spring pressure. The longer those engagement surfaces are, and the rougher they are, the more creep you are going to feel.

Another factor is the trigger pull force. It is the summation of several forces. There is some friction between the sear and the hammer, and the heavier the hammer spring the more this drag will be. Then there is the trigger spring itself.

So to get improved trigger feel, either by upgraded factory parts or trigger work by a gunsmith, there are a number of things that can be done. Going back through the items, starting with pretravel - Metal can be added to either the trigger or the sear, so that the trigger contacts the sear much earlier in it's travel, maybe the instant it starts to move.

Next the creep - the contact surfaces between the sear and hammer may be reduced by grinding (usually by hand with a stone) so the sear has to travel a shorter distance before the hammer is released. The surfaces are also usually polished so they are very smooth. This removes any grittiness felt.

Trigger pull weight - some of the springs may be changed out. If a lighter hammer spring is installed to reduce pull weight, the hammer itself may be lightened as well so it still gets sufficient speed to dent the primer. Or the trigger spring itself may be replaced with a weaker spring. If you go too light, the trigger may not reset quickly or at all.

There are other factors, these are some of the big ones. Installing factory upgraded parts is usually straight forward. Custom trigger jobs are a mixture of machining and art, and lots of practice to get them the same every time.

I can think of several reasons why they don't put match triggers in everything - first, the parts may be more expensive to make, because they are held to tighter tolerances. Or maybe they cost the same, but having a match trigger is just another option they can use to increase profit on the handgun. Another possibility is that the match triggers usually also require less force to pull them, and some buyers may specify a stronger trigger pull for safety reasons.

[Peter Venkman]

Thx AviatorDave. That helps put things in perspective.

I think I'm going to take one of my old USPs and sacrifice it on the alter of learning. I'll never really understand it untill I take it all apart and put it back together.

Thx again

[AviatorDave]

Thx AviatorDave. That helps put things in perspective.

I think I'm going to take one of my old USPs and sacrifice it on the alter of learning. I'll never really understand it untill I take it all apart and put it back together.

Thx again

That's the spirit!

Here's a link to the USP armorer's manual if you don't already have it. It's not one of their best manuals, but it will help if you get stuck:

http://www.ar15.com/content/manuals/USP_Armorers_Manual.pdf

[Peter Venkman]

I found a great DVD that was just what I needed.

Complete HK USP: Disassembly & Reassembly put out by GunVideo (not to worry; Lenny Magill does not appear in this video).

Gunsmith Robert Soldenski goes step by step taking the whole thing apart and explaining the function of each part along the way. He lays out the firing group and explains how the parts articulate and fit together.

If you're a noob like me and want to know all the parts actually work together this is a worth while investment.