Help with AR 5.56 with light trigger strikes

[B!ngo]

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 primers. (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

[vlady]

Did you make sure the hammer spring is installed correctly? Most of the time that's the culprit

[machrono]

No offence to your building skills but I have seen home made lowers with hammers that were off center enough to just barely rub the inside of the bolt carrier, resulting in light primer strikes. Something to check at least.

[B!ngo]

I'll re-check. Like I said (or implied) I've fired this build before. At least I think I have (geez, growing age is such a pleasure).
Oh, and no offense taken. Please add any ideas or comments no matter how trivial or unlikely they may be.
Thx,
B

[liber]

When you say swap the stock, did you change the buffer tube, spring, or buffer?

Or did you just change the stop on the buffer tube?

The tube/spring/buffer could have an effect how how the rifle cycles.

[Nathan Krynn]

The AR platform uses a free floating firing pin. With that when you charge the weapon the firing pin moves under inertia and leaves an indent on the primer. Unlike other weapon systems this does not mean it was a light strike. This is also why you should reload with a primer with a heavier cup such as a #41 primer.

Doesn't mean its not a light strike, it just means that an indent on a primer from an AR-15 doesn't tell you anything really other then the firing pin is moving like it should.

[ar15barrels]

Just to be clear, a light strike is a strike caused by the hammer striking the firing pin and the firing pin failing to light the primer.
Do not confuse the chambering mark from the floating firing pin as a light strike.
If you pull the trigger on a live chambered round and get no bang, that's a light strike.
A dent in the primer after chambering but not firing is a chambering ding.

[BT JUSTICE]

Could your firing pin be worn, bent or defective (too short)?

[B!ngo]

Just to be clear, a light strike is a strike caused by the hammer striking the firing pin and the firing pin failing to light the primer.
Do not confuse the chambering mark from the floating firing pin as a light strike.
If you pull the trigger on a live chambered round and get no bang, that's a light strike.
A dent in the primer after chambering but not firing is a chambering ding.

Randall, you're helpful as always. But I'm not sure that I'm following. The process went like this:
1. Put one round in the mag
2. Cycled the charging handle
3. Flipped from 'safe' to 'fire'
4. Pulled the trigger and deafening silence.
5. Waited 10-15 seconds, flipped back to 'safe', ejected the round and found a small 'divot' in the primer.
Repeated the process a few times with different branded ammo, different mags, lubing up the BCG and still a failure.
I also (carefully) separated the lower and (with my finger blocking the hammer landing point on the receiver), pulled the trigger and it 'fired' as I believe it should (without of course being able to measure the impact pressure - but it hurt - which is standard for this test).
Now I will say one more thing that might be clueful. After getting home, I pulled it apart, disassembled the BCG, lubed it up and reassembled. When slipping the 'bolt' in to the carrier it seemed tight. I finally got it in, put the bolt lug, fringing pin and cotter back in. I then started the shake test. That is, I believe that you should be able to old the BCD and kind of 'whip' your arm and the bolt should move to the 'fire' position. It was pretty tight and took some time working it in to be able to moderately pass the 'test'. Is that relevant? Is there a simple fix for this?
Thx,
B

[SoCal Gunner]

To compare your "light strike" with a "chambering ding", load a mag, chamber and eject a couple rounds WITHOUT firing or attempting to and compare the primer dents.

[xfer42]

Sounds like the carrier isnt moving all the way forward. Does this only happen with a round thats been chambered manually?
Try chambering by hitting the bolt release. If the bolt and carrier are new, then its gonna be a bit stiff until you get some rounds through it.

[Nathan Krynn]

To compare your "light strike" with a "chambering ding", load a mag, chamber and eject a couple rounds WITHOUT firing or attempting to and compare the primer dents.

Bingo.

[B!ngo]

Bingo.

Got it. Will do.
B

[B&D]

It's incredibly rare... Was this a new barrel? If it is I've ran across 3 bbls over the course of a few years that were short chambered. Bolt wont lock up fully enough to fire (thank god) and causes a light strike. Cycles ammo fine but fails to fire. As others have mention check to see if the bolt fully closes on a round. Check the closure of it empty and compare it to a round (preferably not a live one if your not at a range) and see if it fully locks up. The bolt acting "stiff" is the gas rings grabbing the inside of the carrier where it goes. That's normal and good. Bolt should be fully extended on a table and it should not rotate and close on its own when rested assembled on the head. Any reputable smiths in your area? Have him check your head space, i know it sounds dumb but it rarely happens.

[ar15barrels]

The process went like this:
1. Put one round in the mag
2. Cycled the charging handle

Loading the rifle in this way often causes problems.
The proper method to load the chamber is to lock the bolt OPEN, insert a loaded magazine and then depress the bolt release.
When you pull the charging handle back and release it, the charging handle bounces up and down in the receiver AS the carrier is moving forward and trying to chamber a cartridge.
The extra DRAG of the charging handle slows the carrier so that it won't fully chamber.

See if the gun still has a problem if you leave the charging handle forward and release the bolt to chamber the cartridge.

If it still does, I need more history.
Is this an 80% lower or a factory machined lower?