First rounds through it today!  It didn't blow up, which I consider a win.  Accuracy was OK; probably some combination of operator error and the $35 reflex sight I put on it.

Functioned pretty well; no FTFs or FTEs, went "bang" every time it should have, didn't go full-auto.  One thing that concerned me a little was that on an empty mag, the BCG would lock, but not *all the way* back...  It would end up about an inch forward of full back.  Since I didn't have any FTFs, I figure it's cycling all the way; maybe my mag springs are weak?  I was using GI ten-rounders that are at least 25 years old...  One of them wouldn't lock the BCG at all.

Regardless, I had fun, and now I want to see what it can do with a decent scope...

I've taken a few more range trips with it since then, and the bolt still isn't locking all the way back.  The bolt catch catches on the forward edge of the BCG, not the bolt.  Any thoughts about possible causes/solutions?  What I've seen on the inter webs so far seems to indicate it may be undergassed.  Different weight buffer and/or spring, maybe?

I've taken a few more range trips with it since then, and the bolt still isn't locking all the way back.  The bolt catch catches on the forward edge of the BCG, not the bolt.  Any thoughts about possible causes/solutions?  What I've seen on the inter webs so far seems to indicate it may be undergassed.  Different weight buffer and/or spring, maybe?

How did you check to make sure the gas block is aligned with the gas exhaust hole in the barrel?  There are tools designed to do that, or you can use a small rubber tube to blow into the gas block side.  As you rotate and slide the block. you'll get more or less resistance as the holes line up or move apart.  You want it where the resistance is the least to ensure you get full pressure to the action.

Hope that helps.

Start off with the easy things first.
Change magazines. Use ones that are known to work.
Ammo used? Try different manufacturers.

Sounds like a gas problem to me.

I say pull the gas block and take some measurements to try to verify that the hole in the gas block lines up with the barrel gas port. The hole in the gas block should be bigger than the gas port allowing for some wiggle room.  Make sure your gas tube is centered in the upper and not pulled to one side by the barrel nut.


If you have a collapsible "carbine" type stock, you should be using a standard carbine buffer. Rifle needs rifle.

Sounds like a gas problem to me.

I say pull the gas block and take some measurements to try to verify that the hole in the gas block lines up with the barrel gas port. The hole in the gas block should be bigger than the gas port allowing for some wiggle room.  Make sure your gas tube is centered in the upper and not pulled to one side by the barrel nut.


If you have a collapsible "carbine" type stock, you should be using a standard carbine buffer. Rifle needs rifle.

What he said.  If you read the instructions for initial adjustment for an adjustable gas block, you are  supposed to close the port until the bolt fails to lock back.  Then you open it a 1/4 turn and test.  Adjust and test until the bolt locks back, adjusting as many times as it takes to get enough gas to lock back.

That sounds like your problem -- system is getting too little gas.

Heavier buffers are designed to slow down the cycle rate of the BCG in cases where the rounds are not chambering properly.  If the cycle rate is too fast, the BCG can literally bounce out of battery after being pushed into battery by the buffer spring and buffer.  A heavier buffer can prevent the BCG from bouncing back. 

The rate of cycle can be adjusted if you installed an adjustable gas block.  The ones I used work very well, though I've heard from others there are adjustable ones they don't like for some reason.  Some AR's even come with gas system adjustment knobs to accommodate very dirty rifles you can't stop to clean, and suppressors which may cycle better and more quietly with less gas driving it.

Gen II - .750" Adjustable Low Pro Solid Gas Block from Syrac Ordinance.

http://www.syracordnance.com/collections/all/gas-blocks

I ordered 2 at once, and shipping was $5.95 to Hawaii.

So, focus on the amount of gas being delivered through the gas tube and gas block.  Sounds like it's not enough.

Thanks for the answers.

How did you check to make sure the gas block is aligned with the gas exhaust hole in the barrel? 

It went something like "That looks about... wait... wait...  right there!  That's probably close."  And tighten the set screws.   

The gas tube lines up well with the barrel nut, with a little bit of play when the bolt's not in battery.  Found a gas block alignment solution at Brownell's for ten bucks...  Sounds like a winner.  I'll let you all know how it goes.

Thanks for the answers.

It went something like "That looks about... wait... wait...  right there!  That's probably close."  And tighten the set screws.   

The gas tube lines up well with the barrel nut, with a little bit of play when the bolt's not in battery.  Found a gas block alignment solution at Brownell's for ten bucks...  Sounds like a winner.  I'll let you all know how it goes.

If you don't want to wait for Brownell's, another way is the use a pencil to mark the gas port location on the barrel (a line that extends beyond the gas block which should be center of the barrel). 

Then mark the location of the gas port hole on the gas block on its edge.  Again, this should be the center of the block.

Now when you slide the block on, line up the two marks, and make sure the block goes all the way toward the rear of the barrel until it's flush with the "stop" for the gas block.  You should be sliding it as far back as it goes, and then only have to worry about rotating left/right to match the pencil marks.

There's nothing magic about the Brownell's installer.  It's a plastic pin that has a notch.  Together, the two halves are the right length to let you align the ports with the barrel upside down.  When the holes align, the plasic pin keeps the block  from twisting.  You turn the barrel upright, and then use a cleaning rod to break the pin in half so you can remove it.

Yep, I watched the video on Brownell's.  I don't think I'll have it to the range before the tool shows up, so no big deal to wait.  It hasn't yet had a feed failure, so if the zombie apocalypse happens between now and then, I'll just have to be careful with reloads. If I put a fresh mag in with a little bit of force, the bolt releases by itself, which I guess saves me a step...

I'll spend the time while I'm waiting for the order to arrive sanding out the stock on my Ruger American to make sure the barrel stays clear of it...

One thing you might also want to check if you haven't already is the amount of coils on the buffer spring.  If there are too many coils, that can cause you to short stroke your bolt.

Also check the gas rings on your bcg to make sure that you have a proper seal.

One thing you might also want to check if you haven't already is the amount of coils on the buffer spring.  If there are too many coils, that can cause you to short stroke your bolt.

Also check the gas rings on your bcg to make sure that you have a proper seal.

For reference, this is an improper seal ...



 

Problem I had with one barrel was some machining flash left in the gas port. 

Ran the correct size drill through the port to knock the burrs off, cleaned the bore, and all cycling issues vanished.  Was choking off the gas just enough to slow the cycle.

Stock (collapsible), buffer, and spring all came together, so I hope they're properly matched. How many coils would I be looking for on a carbine spring?

Ill check the gas port when I get it apart (once the alignment tools show up).

Start off with the easy things first.
Change magazines. Use ones that are known to work.
Ammo used? Try different manufacturers.

Try a different BCG just to eliminate that link before you take apart your rifle. I had a new build that wouldn't cycle at all, I swapped BCGs with another rifle and both rifles have functioned without issues since.

Try a different BCG just to eliminate that link before you take apart your rifle. I had a new build that wouldn't cycle at all, I swapped BCGs with another rifle and both rifles have functioned without issues since.

Thanks for the suggestion.

I've only got the one BCG, so it's way cheaper for me to get the alignment tool and remove/replace the gas block.  If that doesn't do it, I'll probably try new mags, then maybe a BCG.

For reference, this is an improper seal ...



 

I think that's the kind seal I have.