New AR Not Holding Bolt Open

[huntpnw35]

Hey Guys,

I just put the first 20 rounds through my new AR build and out of 6 mags only had one successfully lock the bolt back after the last round. No other issues with cycling or ejecting just having trouble with the last round.

It's an 18" barrel chambered in .223 wylde and I was shooting 55gr hornady v-max.

Any thoughts on what might be going wrong? My initial guess is the 55gr might be too light.

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[Hueco]

What types of mags (all the same or different manufacturers)?

Recoil system and gas length?

 

[titsonritz]

Assuming proper lubrication and good mags, could be under gassed, either by ammo or gas port/block.

 

[Certaindeaf]

Probably the gubbins.

 

[arrowshooter]

Recoil system and gas length?

Ditto this plus where is your brass going?

Assuming it's rifle length, a simple buffer change could solve your issue if you have the room to go down. I have actually had to remove the weights, ending up with a 1oz buffer, to get an 18"- rifle gas to run right.

 

[titsonritz]

Ditto this plus where is your brass going?

Assuming it's rifle length, a simple buffer change could solve your issue if you have the room to go down. I have actually had to remove the weights, ending up with a 1oz buffer, to get an 18"- rifle gas to run right.

Than something is not right, my 18" w/ rifle length runs fine with a A5H2 buffer (5.33oz) and a rifle buffer (5.1-5.3oz). Shouldn't have to go down to 1oz, hell, a standard carbine buffer is 2.9oz, I don't use them...H min.

 

[arrowshooter]

Than something is not right, my 18" w/ rifle length runs fine with a A5H2 buffer (5.33oz) and a rifle buffer (5.1-5.3oz). Shouldn't have to go down to 1oz, hell, a standard carbine buffer is 2.9oz, I don't use them...H min.

Roger that 100%, a lighter buffer is the simplest remedy leading up to drilling the gas port to correct a slightly under gassed situation. In the case that I mentioned I went up two steps on the gas port and then ran an H1 buffer

OP, make sure that your bolt stop is operational.

 

[Certaindeaf]

Bolt stop/catch engaging fully dry cycling?

 

[Hooyah DeepSea]

What is actually happening is that your bolt carrier is travelling sufficiently to extract and eject, but not travel far enough to engage the 'stop' block on the magazine follower. There are basicly only four reasons for this; (1) insufficient gas pressure / volume, (2) excessive spring tension, (3) excessive bolt carrier / buffer weight, (4) everything is just too dang dry. There are a number of other little possibilities, but those are the big four, assuming you have decent magazines.

Is the rifle a 'build' or a 'bought' ?

What length gas system ?

Is it properly lubed ?

 

[Stomper]

Probably the gubbins.

Bolt stop/catch engaging fully dry cycling?

Those damned gubbins always hit you and go in dry.

 

[Knobgoblin]

Your AR is identifying as an AK .

 

[Snip]

Here's how to set up your gas block: AGB Setup