description of fire control engagement sequence

[Sabo]

(I'd posted this on the Gunsmithing forum, but maybe it's more general in nature and not such a "smithing" question)

With most semi-auto weapons I've function checked, when I cycle the action while holding the trigger back, a sear (don't know the name of this one) would catch the hammer, and then as I let the trigger forward, this sear drops the hammer to the primary (?) sear. I have an Astra-100 9mm pistol that this does not happen to as I "hand-cycle" it (the hammer ends up riding the slide forward), but if I take it to the range and live fire it, it works fine and is ALWAYS SEMI-auto.
Now the FAL question: yesterday, I put in some "top" quality, "best you can get, US made" internals (trigger, sear, disconnector) into an Austrian STG-58 lower. About half of the times when I hand cycle the action while holding the trigger, the hammer will follow the bolt carrier forward. Can't take it to the range until this weekend. Do you think my rifle will malfunction, or will it work just like my Astra pistol. What's been ya'lls experience?

Just a yes or no would be fine, does your hammer, on occasion, ride the bolt carrier forward as you hand cycle the action while keeping the trigger back?
Thanks
Sabo

[ October 19, 2001: Message edited by: gary.jeter ]

[Chief351]

I had exactly the same problem with mine. And not intending to slam anybody - I understand that sometimes with gun parts a little hand fitting is necessary - I am talking here about the DSA trigger-hammer-sear set.

On the FAL, the sear pivot hole is slightly oval-shaped. With the trigger at rest and the hammer cocked, the rear of the sear rests over the little 'shelf' on the rear of the trigger. The front of the sear, of course, is engaged in the sear notch on the hammer.

When you pull the trigger, the shelf tilts the rear of the sear up and causes the front of the sear to drop to release the hammer.

Now the critical part! With the front of the sear clear of the hammer, the small spring between the trigger and sear pushes the sear forward. The oval slot where it pivots allows for this forward movement. It has to move sufficiently far forward that the rear of the sear can drop down into the 'valley' on the trigger and ahead of the shelf, allowing the front of the sear to rise back up ready to catch the hammer. This forward movement is what causes the 'disconnector' action to happen.

When the bolt cycles and re-cocks the hammer, the cocking notch on the hammer catches the front of the sear, and the hammer spring overpowers the little spring that originally pushed the sear forward. In effect the hammer itself now pushes the sear back. The sear can't go completely back to its starting position yet because the rear of the sear is now against the front of the trigger shelf, not on top of it.

When you finally release the trigger, the rear of the trigger, and consequently its shelf, now drop out of interference with the sear. The hammer spring pushes the sear backwards some more so that its rear end is now back on top of the trigger shelf. You will actually see the hammer 'jerk' slightly when this happens.

Now the whole system is reset for the next shot.

What's happening with yours is this: When you pull the trigger for the first shot, the sear is disengaging the hammer OK but the sear isn't being allowed to move forward far enough to get clear of the shelf on the rear of the trigger. This allows the trigger to continue to hold the front of the sear down too far for it to catch the hammer when it is re-cocked by the slide.

To fix the problem, the little oval slot in the sear will have to be filed EVER SO SLIGHTLY so as to allow the sear to move that slight amount forward as I described above. You need to open the slot up towards the rear, or towards the end that engages the trigger.

If you have the original sear that came with your parts kit, take the original sear and the new one out and hold them up against each other. You should be able to see that the slot on the new sear is slightly undersized. This will give you an idea of how much metal has to be removed.

Hope this gives you the answer you need.

[Sabo]

I'm completely overwhelmed. I never would have expected such a thorough response. Chief, you're an asset that makes this website the top quality place that it is and I've come to learn.

Funny, when I first looked at the sear and saw that slight oval, I had hoped it wasn't a manufactoring defect, but assured myself that it must have been part of the designer's "grand design." Now it's the case where it might not be oval enough! (I'll have to check it this evening against the Century part) What type of bit or filing method did you use to successfully fix yours? Looks like I'll be stopping at the hardware mart on the way home!

[Deltaten]

Sabo:

I agree w/ you about the reply from the Chief! To the extent that I downloaded and printed up for future ref. Thanks Chief!

As to the answer; you get what you ask for, Sabo. You asked a precise and well phrased question. Chief answered in a like manner. A lot of "it don't work" questions get asked here, w/resulting flaming answers and re-replys asking for more info.

Thanks to you both for the clarity,
Paul

------------------
They call us the"Right", don't they?

[Chief351]

Sabo - I have a set of "Nicholson Miniature Files NO. 42030". There are six files in a little plastic pouch, and the whole set is small enough to fit in your shirt pocket. These are very fine-tooth files. I believe I bought them at a Home-Depot type store. I would expect that any decent hardware store would have something similar. Anyway, there's an assortment of flat, half-round, rat-tail, triangle, etc.

Thanks for the complements on my answer. Just trying to share the wealth, you know.

P.S. Best to keep the FAL and the Dremel tool always in seperate rooms! I'll bet that more guns have been ruined with Dremel tools than by all other tools, accidents, etc. combined. Remember, once you take the metal off it's really hard to put it back on!

I also think that you want to make sure that, when filing out the little oval slot, keep the back surface of the opening 'square', that is, not at an angle. If it's angled, the sear will have a tendency to shift into a crooked position and will probably not give good results.

Good luck!

[This message has been edited by Chief351 (edited December 27, 2000).]

[DriftPunch]

Sabo, Wazzup!

Keep an eye out for posts referencing Bubba's shoot on the 21st of Jan.

Oh yeah, I forgot that you may not know me by this name. This is my primary name. The only board where I don't post by this name is AR15, where I go by Col.Krink!

[This message has been edited by DriftPunch (edited December 27, 2000).]

[jim]

very informative post from cheif.
however i had experienced the same problem with another mfg hamer and sear. after cleaning them up (smoothing out all contacting surfaces) i still had the same problem. until i discovered that i had switched the trigger and sear spring! it really didn't click that there was something wrong when i had one hell of a time reinstalling the trigger/sear unit, with the pin. as this unit is usually a 1 handed operation. after walking away and thinking about i realized that i had the springs mixed up!!
will it work for you? maybe maybe not. but i do like the info cheif gave to us
thanks for sharing.

[Sabo]

Epilogue:

Jim, thanks, but I knew it wasn't a spring problem since I hadn't disassembled any similar springs such as the trigger spring.

Chief, well, after a couple hours of attention - disassembling the new parts and reassembling in the old functioning parts to observe how they properly operate together, then disassembling and reassembling the new parts to see how they weren't working together - it was just as you described. Now, I've just finished carefully removing a bit of metal as you recommended. And the pivot hole WAS smaller than the functioning original piece. But it works like a charm now!! http://www.fnfal.com/forums/smile.gif Thanks again, you really saved a very big crisis for me at the range. If I hadn't caught the improper operation with a function check, could the condition have caused an ugly event? Could it have resulted in an out of battery ignition? (A great design against out-of-battery is one reason why I love the AR-15/M-16 design).

I'm glad the military drilled in me the importance of doing such checks!

[Sabo]

Hiya Driftpunch,

Nice to hear from you. I'll try to keep the 21st clear. Where'bouts in 'Giny is Bubba?

Yes, I remembered your callsign was Driftpunch. Is there a story behind it?

[W.E.G.]

btt