Help with light trigger strikes please?

B!ngoFuelUSN · Jul 19, 2015

Hello,
I took one of my home-made (left handed with Stag upper, lower and BCG) AR 5.56's (the gun also has a Geissele SSA-E trigger installed) to the range today.
I've not shot it in a very long time, perhaps never in this configuration (I use this gun to experiment with new parts) and decided to take it to the range today. It didn't fire and looks like light trigger strikes as there were small dents in the primer. (By the way, the last change I made was to swap the stock. Nothing in the FCG).
I tried changing ammo (no help); changing mags (nope); pulling the BCG and lubing it up pretty well (no); finally I disassembled the BCG, lubed all of the components and reassembled it. I also experimented with the trigger, blocking the hammer with my finger so it didn't hit the receiver. I can't tell if it was firing with enough strength but it did seem to work properly. I still didn't fire and the primers showed the same light strike evidence. I just packed it up.
So, I'm looking for guidance as to where i should look first. I assume a full assembly and a good dunk in cleaner followed by a good lube I should add that when I pulled the BCG and 'shook it', the components didn't seem to move as freely as I thought they should.
Thanks in advance,
B

243winxb · Jul 19, 2015

Geissele SSA-E trigger 2nd Stage Weight: 1.2lbs.

Could the light trigger pull weigh be letting the hammer follow the bolt? I would guess, no lube should be on the hammer/sear engagement. Just my guess??

BBBBill · Jul 19, 2015

B!ngoFuelUSN said:
...the last change I made was to swap the stock....

Start there. What did you change?

JohnKSa · Jul 19, 2015

Ok, here are some of the things that can cause the problem.

1. Hammer is too light. If you have lightened the hammer (or installed a lighter hammer) you probably need a stronger hammer spring.
2. Hammer spring is too weak. Could be a bad spring or it could be that it's not suitable for the hammer weight.
3. Something is obstructing hammer travel. It could be being pinched so that it can't move freely or it could be catching on something.
4. Something is obstructing firing pin travel. Could be fouling or obstruction in the bolt or the firing pin could be damaged or deformed.
5. Firing pin may not be long enough--to little firing pin protrusion. If not enough of the firing pin protrudes from the boltface it won't fire the rounds.
6. Rounds are not fully chambering. If the rounds are oversized or the chamber is undersized, the rounds won't fully chamber and the safety interlock may prevent the firing pin from traveling fully forward.

B!ngoFuelUSN · Jul 19, 2015

JohnKSa said:
Ok, here are some of the things that can cause the problem.

1. Hammer is too light. If you have lightened the hammer (or installed a lighter hammer) you probably need a stronger hammer spring. - it's the stock hammer with the Geissele SSA-E kit and it's worked for me just fine in other applications.
2. Hammer spring is too weak. Could be a bad spring or it could be that it's not suitable for the hammer weight. It is the stock spring with the kit. And though it could be defective, it's Geissele. Their stuff is more dependable than the sun rising and falling.
3. Something is obstructing hammer travel. It could be being pinched so that it can't move freely or it could be catching on something. - Yes, I checked that and it is moving in its full arc. In fact, it is producing light strikes with small dents on the primer.
4. Something is obstructing firing pin travel. Could be fouling or obstruction in the bolt or the firing pin could be damaged or deformed. - Thus a comprehensive cleaning.
5. Firing pin may not be long enough--to little firing pin protrusion. If not enough of the firing pin protrudes from the boltface it won't fire the rounds. - Yea, this is the one that worries me. How can I tell. It 'looks' like another once I have (see below) but I guess I'd need a chamber head space thingie.
6. Rounds are not fully chambering. If the rounds are oversized or the chamber is undersized, the rounds won't fully chamber and the safety interlock may prevent the firing pin from traveling fully forward. - unlikely since this gun has worked with the same barrel, upper receiver and trigger.

First off, thanks JohnKSA and all the other contributors. Here's what I've done so far:
1. I pulled its 'clone' from the safe. Clone being same stripped upper and lower receiver, same SSA-E from Geissele, different barrel though. This gun has always worked perfectly.
2. I pulled BCD's from both and tried to compare firing pin protrusion when 'pressed' (simulated hammer firing and they appear to be identical).
3. I disassembled and completely ultrasonically cleaned all of the standard parts (keeping the two BCG parts separate) and then reassembled keeping them fairly ''wet'.
4 A question is whether I could measure 'head space' without buying the measuring tools to do so. Is there a simple way to ensure that the firing pin is adequately protruding and that the round is seated in the right location with respect to the bolt?
I'm very careful when I build things and it really bugs me when they don't work. I've got to get this fixed. Especially since I have another project backed up on this rifle once I get it working again.
I won't be able to re-test until Wednesday. Dang.
Thx,
B

BBBBill · Jul 20, 2015

B!ngoFuelUSN said:
... A question is whether I could measure 'head space' without buying the measuring tools to do so. Is there a simple way to ensure that the firing pin is adequately protruding and that the round is seated in the right location with respect to the bolt?...

Not really, although some folks use some cobbled up stuff to measure headspace. Better to buy, rent, or borrow the correct gauges. Not likely to be your problem anyway. Firing pin protrusion can be measured with a simple gauge, either bought or scratch built and is independent of headspace. Key with an AR is to ensure that the bolt is fully rotated into the locked position when checking protrusion AND to ensure that it locks that way into the barrel extension when assembled for firing. Get a copy of the Army TMs that cover M-16 maintenance for guidance.

JohnKSa · Jul 20, 2015

If you have another AR, you can swap out uppers. If the problem follows the lower then it's something to do with the hammer/hammer spring or something obstructing/pinching the hammer in the lower receiver. If it follows the upper it's something to do with the chamber/firing pin/bolt/ammo.

If it's the upper, you can swap bolts to see if it's something related to the bolt or firing pin. If you're going to swap bolts, you should insure that the headspace is good with the different bolt installed. It should be, but to be safe, I feel like I should say it anyway.

B!ngoFuelUSN · Jul 20, 2015

JohnKSa said:
If you have another AR, you can swap out uppers. If the problem follows the lower then it's something to do with the hammer/hammer spring or something obstructing/pinching the hammer in the lower receiver. If it follows the upper it's something to do with the chamber/firing pin/bolt/ammo.

If it's the upper, you can swap bolts to see if it's something related to the bolt or firing pin. If you're going to swap bolts, you should insure that the headspace is good with the different bolt installed. It should be, but to be safe, I feel like I should say it anyway.

Yes, I agree that this the proper scientific method. First:
Take both to the range and swap uppers and shoot both
Presuming the (previously failed) upper still fails then keep the uppers and lowers as they were and swap BCG's.
If one fails and the other functions, make sure that the working one also functions properly in the 'failed' gun. That will isolate it to the BCG.
Presuming it's the BCG, I'll then, um, well, stick knitting needles in my eyes... Or tale out my Tavor. But the ultimate goal of this 'experimental piece' is to build a CA 'Featureless Rifle' (for those uninitiated, look it up but you can stop reading when your weeping overwhelms you) AND add a Apex Copper Customs barrel conversion kit to swap from 5.56 to 300BLK.
B
EDIT: Again, thanks for all of your help.

Help with light trigger strikes please?

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