Ar build, 2nd round won’t fire?

[davidbschenck]

I built 2 AR 300 blackout pistols and a 223/556
Pistol. I took them all to the range to test them and all 3 fired the first shot, ejected the empty shell & loaded the 2nd round but it wouldn't fire. I looked at the primers and could see a tiny mark where it apparently was struck by the pin but not hard enough to fire? Any suggestions?

 

[mdram]

that mark could be from the pin during cycling.
did the hammer actually fall on the second shot?

 

[davidbschenck]

Great question, I don’t think it did.

 

[Caveman Jim]

Did you use the same magazine on all of these builds?

 

[GuitarmanNick]

If you milled the lowers, there is a possibility that the trigger pocket is not deep enough and is keeping the trigger from resetting. It should measure 1.2490" deep.

 

[6ShotsOr5?]

Are you using drop in triggers or some fully adjustable design? If adjustable, check adjustment of the disconnector.

 

[Fast14riot]

If mil style trigger, make sure hammer spring is installed properly, it is easy to install backwards

 

[jonbearman]

Could it be it didnt lock up? You better run a go and no go gage to be damned sure.I have seen one fired out of battery and it destroyed a old freinds gun.He didnt get hurt real bad but none the less error towards safety. The pin bounce will dink a case and is normal.

 

[whatsupdoc]

If it fired the first round and did not fire the second round here are some possibilities.

If on the second round you herd a "click" of the hammer dropping it is possible the bolt
was not completely in battery.

If you pulled the trigger on the second round and there was no click then either
the gas system is not sending the boltcarrier rearward enough to cock the hammer or
the disconnector is broken, missing not working and the hammer is riding the
boltcarrier into battery. This can cause the rifle to go into full auto.

 

[C.E.Smith043]

If mil style trigger, make sure hammer spring is installed properly, it is easy to install backwards

^^^^ This happens more often than not. Make sure you check this. I'm guilty of installing it wrong myself.

 

[straightShot]

^^^^ This happens more often than not. Make sure you check this. I'm guilty of installing it wrong myself.

Me, too.

 

[SG4247]

Under-gassed.

needs a little more to reset the hammer fully.

 

[davidbschenck]

Did you use the same magazine on all of these builds?

No each had its own mag. The 300 blackouts had specific mags made for that round I’m not sure how different they are but I wanted to make sure the mags weren’t a problem

^^^^ This happens more often than not. Make sure you check this. I'm guilty of installing it wrong myself.

very possible on the 223/556 but the 2 300 blackouts have drop in Rise Armament triggers.

I didn’t mill them and since it’s happening on 3 different AR builds, I think I must have use a wrong, pin, spring etc. in all 3. Someone suggested the buffer may not be heavy enough. I confess I did use $7.99 aero buffers. Pretty sure they are all H2. I ordered an H3 to try, it was $43.00. Hopefully that will make a difference. I don’t really know how the buffer

Did you use the same magazine on all of these builds?

no, seperate mags for each pistol, 300 blackout mags for those.

 

[Twdmar]

First test, load one round in the magazine and see if it locks back. If it does not, you need more gas.
If it does, check your hammer, trigger etc. Let the bolt go forward on an empty chamber and pull the trigger.
If the hammer falls well, make sure the bolt is fully engaging. If the bolt does not fully go into battery, try a couple rounds in the mag. A full mag may slow the bolt down too much. If it doesn't go into battery fully, check buffer springs and resistance from ejector/extractor.

 

[davidbschenck]

I like suggestions like this to try. I will try these at the range and see if learn anything. Not sure how to check resistance from the extractor but I'll ask the range guys while I'm there. They seem to know stuff I don't.

 

[davidbschenck]

If it fired the first round and did not fire the second round here are some possibilities.

If on the second round you herd a "click" of the hammer dropping it is possible the bolt
was not completely in battery.

If you pulled the trigger on the second round and there was no click then either
the gas system is not sending the boltcarrier rearward enough to cock the hammer or
the disconnector is broken, missing not working and the hammer is riding the
boltcarrier into battery. This can cause the rifle to go into full auto.

possible on one but all 3?

 

[davidbschenck]

What is interesting is that I have built a dozen or so of these Aero Precision lowers ( I buy pre made complete uppers from Aero) and they have all worked in the past. I'm thinking I made one mistake in all 3 of these builds. Can't figure out what it was.

 

[Caveman Jim]

Did you use the same gas box on all three? If you did that’s probably your problem, under gassed.

 

[SG4247]

If I had a dollar for every gas port I have re-drilled or gas block I have re-positioned on an AR…

 

[Coyotefurharvester]

First function test the lower, if that operates correctly. You have a gas or buffer issue.