View Full Version : For lack of better terms: Hammer Fallow thru?
A friend of mine bought a complete build, built by someone else. Took it out and it would fire approx 3-4 rnd burst. He had bought a Bushy A2 lower so he put it with the upper and worked fine. I took it home and it seemed to function OK off the upper, and would reset properly with the disconnecter. But when I took it out today it seemed to have hammer fallow threw, it would run several and then stop and there would be one in the chamber, but the hammer would be forward. Swapped the lowers and all ran well with the Bushy lower. Swapped back to make sure and malfunctioned. Swapped the Trigger, hammer, disconnecter, and safety between both lowers. Ran several 30 rnd mags threw both lowers and all was fine. All I could say was WTF? Why the problem didn't fallow to the Bushy lower. Pins all seemed straight, and no slop on either. Seemed to fit the lowers just fine and snug too. I'm going to see about buying the bushy A2 lower from him, and get new FC parts and build a 6.8 later. Any Ideas why this happened and didn't fallow when swapping FC to other lower? JFM? (Just Fricken Magic)
Sorry. Re-read your post and now, I too am puzzled...
Are both FCG's new? THe problem may be the lower being slightly out of spec and the FCG being slightly worn or perhaps have had a trigger job of some sort?
This sounds like a issue of bolt bounce to me. Though I was slightly confused by your testing methods.
A friend of mine bought a complete build, built by someone else. Took it out and it would fire approx 3-4 rnd burst. He had bought a Bushy A2 lower so he put it with the upper and worked fine. I took it home and it seemed to function OK off the upper, and would reset properly with the disconnecter. But when I took it out today it seemed to have hammer fallow threw, it would run several and then stop and there would be one in the chamber, but the hammer would be forward. Swapped the lowers and all ran well with the Bushy lower. Swapped back to make sure and malfunctioned. Swapped the Trigger, hammer, disconnecter, and safety between both lowers. Ran several 30 rnd mags threw both lowers and all was fine. All I could say was WTF? Why the problem didn't fallow to the Bushy lower. Pins all seemed straight, and no slop on either. Seemed to fit the lowers just fine and snug too. I'm going to see about buying the bushy A2 lower from him, and get new FC parts and build a 6.8 later. Any Ideas why this happened and didn't fallow when swapping FC to other lower? JFM? (Just Fricken Magic)
Is it a select fire weapon?
Sorry. Re-read your post and now, I too am puzzled...
Are both FCG's new? THe problem may be the lower being slightly out of spec and the FCG being slightly worn or perhaps have had a trigger job of some sort?
Neither one is new, but there is hardly any wear on the hammer and trigger. They appear to be semi auto parts and the safety only has the one flat side on it, definitely only has safe and fire on the safety and will not move any other than the two positions. I thought about the one lower being just out of "Spec" too, and without any way to check this, I'm wondering if it will repeat itself later on as it wears the parts.
This sounds like a issue of bolt bounce to me. Though I was slightly confused by your testing methods.
Ig: Will bolt bounce pick up another round and chamber it? I thought it just bounced back a fraction of an inch and that was it. Obviously I don't know about BB, but you are an Armorer and know way more than I could dream of, and I appreciate your sharing of your knowledge here on this board.
I didn't have any new parts to swap out, and between the two lowers I could only see that the "Bushy" lower had a notched hammer. I didn't have time to swap each individual part out to see what might be causing the problem, and the bushy wasn't doing it, just the "Fidelis Arms" lower. When I swapped the hammer, trigger, disconnecter, and safety together not separating the FCG parts but keeping them from each lower together as a group, then the "Fidelis" and "Bushy" both fired fine for approx 30 rnds each. To younger eye's they both had the same wear. To my eye's I wondered if the "Fidelis" was just ever so slightly almost imaginable wore just a .001 more on one side of the trigger and hammer, instead of evenly straight across their faces, like maybe the "Fidelis was just .001 off on the pin bore thew the lower. But my old eye's are not that good anymore.
Are you more confused now than before?
Not really. If neither is new, have you tried comparing the wear on both FCG parts or tried measuring both lower pin holes with a caliper?
I had the exact same issue win Iraq with two carbines (select-fire) if I recall. I swapped every part imaginable and was beating my head. Then the experts here suggested it could be bolt bounce (over-gassing situation). When I changed the barrel the problem stopped. It was my guess that the gas port was eroded and since their barrels are over-gassed to begin with it makes sense.
Neither one is new, but there is hardly any wear on the hammer and trigger. They appear to be semi auto parts and the safety only has the one flat side on it, definitely only has safe and fire on the safety and will not move any other than the two positions. I thought about the one lower being just out of "Spec" too, and without any way to check this, I'm wondering if it will repeat itself later on as it wears the parts.
Ig: Will bolt bounce pick up another round and chamber it? I thought it just bounced back a fraction of an inch and that was it. Obviously I don't know about BB, but you are an Armorer and know way more than I could dream of, and I appreciate your sharing of your knowledge here on this board.
I didn't have any new parts to swap out, and between the two lowers I could only see that the "Bushy" lower had a notched hammer. I didn't have time to swap each individual part out to see what might be causing the problem, and the bushy wasn't doing it, just the "Fidelis Arms" lower. When I swapped the hammer, trigger, disconnecter, and safety together not separating the FCG parts but keeping them from each lower together as a group, then the "Fidelis" and "Bushy" both fired fine for approx 30 rnds each. To younger eye's they both had the same wear. To my eye's I wondered if the "Fidelis" was just ever so slightly almost imaginable wore just a .001 more on one side of the trigger and hammer, instead of evenly straight across their faces, like maybe the "Fidelis was just .001 off on the pin bore thew the lower. But my old eye's are not that good anymore.
Are you more confused now than before?
Bolt bounce will not chamber another round and drop the hammer on it... You have a problem with the disconnector/spring or sear engagement.
Check the disconnector spring is present and installed correctly.
Check the trigger and disconnector for burrs.
Check the grip screw, if it sticks up into the FCG area it can limit sear engagement.
What Todd said. A bad hammer can also be the cause. Also, it is possible to have on out of spec lower in which the pin holes are incorrectly located. This causes misalignment of the FCG. I recently came across this.
Bolt bounce will not chamber another round and drop the hammer on it... You have a problem with the disconnector/spring or sear engagement.
Check the disconnector spring is present and installed correctly.
Check the trigger and disconnector for burrs.
Check the grip screw, if it sticks up into the FCG area it can limit sear engagement.
Thanks Todd
Check the disconnector spring is present and installed correctly. On both it was with the large end down under the disconnector.
Check the trigger and disconnector for burrs. Both lowers, parts were smooth-no burs but not smooth as in wore a lot.
Check the grip screw, if it sticks up into the FCG area it can limit sear engagement. Aha: I switched out each grip and spring with the FCG just for S&Gs, but did not check to see if they stick up higher. Both had the lock washer under them. Will do tonight.
Ignz: 16" carbine A2 FH, FSBGB is Not "F" marked but has 26 on it, barell say's "DTI CL 1X9 556 NATO". No idea GP size but it is carbine. I "assume" CL=Chrome Lined. Not sure who DTI is, haven't had time to check.
Could the lower be out of spec just enough that new/other parts will work fine, and then shortly after some use wear, then repeat the problem again?
Ignz: 16" carbine A2 FH, FSBGB is Not "F" marked but has 26 on it, barell say's "DTI CL 1X9 556 NATO". No idea GP size but it is carbine. I "assume" CL=Chrome Lined. Not sure who DTI is, haven't had time to check.
DTI is Del-Ton Inc. I dont know if they come with a slightly larger GP than the USGI TDP spec barrels.
Could the lower be out of spec just enough that new/other parts will work fine, and then shortly after some use wear, then repeat the problem again?
Yes, IMHO. Just as heavily worn parts would cause dual or maybe tri bursts on an up to spec lower. In this case, my thinking behind my initial response on the lower being out of spec was that the hammer could be sitting slightly higher or the trigger lower or even a bit backed off.
Todd,
When I had the issue with our BM's in Iraq I replaced every single part in the lower because replacing the disconnector and spring did not work. After replacing everything to include trying different lowers the problem was still there and I was stumped.
It did indeed fire and did in fact chamber a round. When I opened the upper receiver the hammer was in the forward position. This happened in semi and full auto.
I replaced the barrel and when I did the carbine worked 100%.
I believe that it was GotM4 and Grant that clued me in as to what was happening.
Bolt bounce will not chamber another round and drop the hammer on it... You have a problem with the disconnector/spring or sear engagement.
Check the disconnector spring is present and installed correctly.
Check the trigger and disconnector for burrs.
Check the grip screw, if it sticks up into the FCG area it can limit sear engagement.
It did indeed fire and did in fact chamber a round. When I opened the upper receiver the hammer was in the forward position. This happened in semi auto.
This is exactly what I was experiencing, a live round chambered, and the hammer in the forward position, after 3 rounds fired with one pull of the trigger. But when I took the lower off the upper, and cocked the hammer, pulled the trigger, and while holding the trigger back in the fire position, I manually cocked the hammer again with my left hand, and it would stay cocked, and then when I let the trigger reset, the disconnecter would do it's job and keep the hammer cocked, with plenty of contact to keep from firing again, until the trigger was pulled again.
Why this would only fire in burst with one lower and not the other, I can only ask if the difference in GP size, be the difference in the "Fidelis" being an adjustable stock with a reg carbine weight buffer, and the "Bushy" having the A2 fixed stock and a totally different buffer than an adjustable stock, have anything to do with GP size being handled better with the different (Heavier) buffer in the "Bushy" A2 stock.
Todd,
When I had the issue with our BM's in Iraq I replaced every single part in the lower because replacing the disconnector and spring did not work. After replacing everything to include trying different lowers the problem was still there and I was stumped.
It did indeed fire and did in fact chamber a round. When I opened the upper receiver the hammer was in the forward position. This happened in semi and full auto.
I replaced the barrel and when I did the carbine worked 100%.
I believe that it was GotM4 and Grant that clued me in as to what was happening.
IG, wat barrel length was it? What buffer and spring did it have?
If you dont mind, Im taking a screenshot and keeping this for future reference.:)
14.5" barrels. Standard Bushmaster springs with Bushmaster brand "H" buffers.
IG, wat barrel length was it? What buffer and spring did it have?
If you dont mind, Im taking a screenshot and keeping this for future reference.:)
I don't know why it went into burst mode to be honest. Maybe someone put the wrong fire control parts in there?
I would try and secure a good known upper and see if the same thing happens. At that point I would be in touch with the person who built it, especially if it is firing more than one round when you pull the trigger.
If the hammer is down on a live round in semi there has to be a problem with the FCG.
The difference in recoil from a rifle buffer and spring to a car buffer and spring may be just enough to jar the hammer off less than normal sear engagement.
Todd,
I agree that replacing those parts should have fixed it. It didn't. As I said before I replaced every part in the lower receiver. I even tried different BCG's. The weapon had been previously functioning 100%.
I took an upper from another weapon and it worked. That's when I was stumped. I then took the original upper, put a new BM barrel on it, put the original BCG and FCG parts back on the weapon and it worked like it should.
If the hammer is down on a live round in semi there has to be a problem with the FCG.
The difference in recoil from a rifle buffer and spring to a car buffer and spring may be just enough to jar the hammer off less than normal sear engagement.
Todd,
I agree that replacing those parts should have fixed it. It didn't. As I said before I replaced every part in the lower receiver. I even tried different BCG's. The weapon had been previously functioning 100%.
I took an upper from another weapon and it worked. That's when I was stumped. I then took the original upper, put a new BM barrel on it, put the original BCG and FCG parts back on the weapon and it worked like it should.
? So, IE: with all the original parts and a new barell, (you just changed out the barell in the end) that may have had the right size gas port, and all ran fine?
I swapped out the important parts in the lower and it did not help. After consulting I replaced the barrel with a new Bushamster barrel and it worked like it should. I put the older LPK back in and it continued to work. Since it was a new barrel (though the port may be larger) it was not eroded. Since I didn't have a Hawkeye Borescope I couldn't check the gas port.
I can only relay what my experience was and cannot guarantee it will solve the problem.
What you really need to do is this.
1. Get a KNOWN reliable functioning upper and put it on the lower and test it again. If it doesn't function right then something is wrong with(in) the lower. If it runs correctly I would start to think barrel.
2. I would get a KNOWN reliable lower and put it on the upper and see if the problem persists. This way you have checked potential problems separately.
3. I would seriously consider telling your friend to return the weapon back to the seller.
? So, IE: with all the original parts and a new barell, (you just changed out the barell in the end) that may have had the right size gas port, and all ran fine?
Heavy Metal
05-16-10, 11:23
IG,
Did you try putting a heavier buffer in it?
We didn't have access to heavier buffers. I suggested it, but when the cost factor came into play-500 carbines X xxxx amount per buffer it was shot down.
Getting parts in Iraq and Afghanistan isn't easy and the process can take a while. I needed an immediate fix and had some barrels on hand.
IG,
Did you try putting a heavier buffer in it?
I had the same problem last year with a DTI upper and LPK in a S&W M&P lower. Would get 3-4 round bursts and hammer follow. The gas key also worked loose (didn't check for proper staking prior to shooting). I contacted Del-Ton and they recommended returning the LPK, never heard back from them once I did.
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