Under gassed AR, what can i do?

[American_Fusilier]

So I've got an AR-15 pistol with a 10" barrel, where the bolt won't lock back on an empty magazine.

It's chambered in 5.56, but I mostly shoot 223 out of it. I also have an AR-15 rifle chambered in 5.56 through which I also mostly shoot 223 out of.

Both ARs have carbine length gas systems, standard buffers and buffer springs, and both lowers were assembled by me and I purchased the uppers. The rifle upper is a PSA the pistol upper is BCA.

I know my rifle is slightly over gassed, and it appears my pistol is slightly under gassed. The rifle functions 100% (in fact has never had a stopage of any kind). The pistol never short strokes while shooting ammo, but the bolt never gets far back enough to get caught by the bolt catch.

What are my options to fix this? I don't want to take apart my gun and bore the gas hole bigger.

What else can be done? Do you guys know of any other solutions?

 

[LoonWulf]

Could go to a lighter buffer/spring combo

 

[skeeterfogger]

Lighter buffer spring.

 

[mcb]

First make sure you have nothing dragging like the roll pin in the buffer back out or something similar. Then if everything is in good shape a lighter buffer might work. Make sure you have standard carbine buffer in it first and not an H1, H2, or H3 heavier buffer. A lighter spring probably won't do much unless you are already on the ragged edge of running correctly.

The best solution IMHO, though certainly not the easiest, is to enlarge the gas port in the barrel to the next number-size drill bit bigger than what it currently is and try function again. Rinse and repeat as needed until it cycles the way you want.

 

[C-grunt]

Check for a gas leak in the BCG.

 

[MistWolf]

First, check to make sure it locks back when operating the charging handle manually

Second, stop using under powered ammo. Test your AR using full power 5.56

Third, check for leaks blockages and misaligned parts in the gas system

Fourth, don't waste your time playing with lighter buffers & springs. A properly gassed AR wil be fully functional with a standard spring and an H2 buffer, using full power ammo. Palmetto kits ship with a carbine weight buffer, which is too light

Fifth, when (not if) you start getting empty cases caught in the action, replace the extractor spring with one from Colt or Sprinco- no O ring! Accept no substitutes

 

[MistWolf]

PS- DO NOT open up the gas port until you've exhausted all other possibilities

 

[mcb]

PS- DO NOT open up the gas port until you've exhausted all other possibilities

Right but once you have eliminated all other potential causes opening the gas port up (slowly with testin) is the best solution to an under gassed gun. I would rather have a slightly over-gassed gun than under-gassed. It's easier to slow an over gassed BCG down than speed up an under-gassed BCG.

 

[Varminterror]

First, check to make sure it locks back when operating the charging handle manually

Second, stop using under powered ammo. Test your AR using full power 5.56

Third, check for leaks blockages and misaligned parts in the gas system

Fourth, don't waste your time playing with lighter buffers & springs. A properly gassed AR wil be fully functional with a standard spring and an H2 buffer, using full power ammo. Palmetto kits ship with a carbine weight buffer, which is too light

Fifth, when (not if) you start getting empty cases caught in the action, replace the extractor spring with one from Colt or Sprinco- no O ring! Accept no substitutes

PS- DO NOT open up the gas port until you've exhausted all other possibilities

This, and in this order.

Gas and mass have to be balanced, and the spring is the voyeur watching the action from the corner. Your rifle is under gassed, not over massed or over sprung, so fix what’s wrong... most often you have something binding, second most often you have under powered ammo, third most often you have a leak and a long, long distant fourth place you legitimately have an undersized port to operate a standard weight reciprocating mass’s

 

[js8588]

Send the upper back to BCA. It has a warranty, use it.

When they send you a new upper, sell it on GunBroker. Don't test it, just sell it. In this market it'll go for more than it's worth. Use the proceeds from the sale as a base to buy a quality upper from literally almost anyone else except radical firearms.

 

[d2wing]

Could be the latch on the lower.

 

[Zerodefect]

Drill! Baby, yeah.

 

[BreechFace]

Some other odds and ends that didn't get mentioned.

-Make sure your gas tube is lined up to meet your gas key and it’s not dragging
-Double check your gas rings on your BCG, in the extended position they should hold the weight of the BCG vertically without collapsing
-Gas block alignment to gas port

This is why I like to assemble my own AR's, too many companies with trained monkeys racing to see who can get the most AR's out the door. Personally, I would disassemble the whole upper and reassemble from scratch verifying gas port diameter, centering of the gas block to the gas port, gas tube alignment with BCG, barrel nut torque, BCG health, re-lube all key points, and run the BCG wet with some m193 NATO rounds with a known good magazine.

Too many variables, better time spent unassembling, verifying key points and reassembling, but I don't know what type of skills or tools you have.

 

[12Bravo20]

I have to agree with MistWolf and Varminterror. I always use M195 or M855 ammo for the first 100 rounds or so on any new build. Sometimes (but not always) 223 ammo is loaded a bit weaker than true 5.56 ammo. And yes check the gas block and gas tube alignment and gas tube to gas key alignment along with any gas leaks. I also agree that you should check the gas rings on the bolt too as BreechFace said.

 

[Ru4real]

Under gassed?

Bigger carburetor jets? I’m new at this.

 

[12Bravo20]

Under gassed?

Bigger carburetor jets? I’m new at this.

Under gassed when talking about the AR gas system means that there is not enough gas getting to the bolt carrie group to push it back far enough to eject spent cases or feed new round from the magazine.

Some of the usual causes of this is having a gas leak, misaligned gas block, bad gas key, bad gas rings on bolt, or the gas port on the barrel is too small.

I suggest reading up on how the AR works to understand it fully.

 

[MistWolf]

Right but once you have eliminated all other potential causes opening the gas port up (slowly with testin) is the best solution to an under gassed gun. I would rather have a slightly over-gassed gun than under-gassed. It's easier to slow an over gassed BCG down than speed up an under-gassed BCG.

and Black River Tactical has a couple three excellent fixes for over gassed barrels

 

[Demi-human]

Bigger carburetor jets?

Exactly.
The gas port is the jet orifice and the cartridge combustion gasses are the fuel.
If the jet isn’t big enough, not enough fuel(pressure) will reach the piston in time to move it, or in this case, move it far enough.


The worst is over gassed. That costs money to fix...

 

[skeeterfogger]

A guy I met at my range shoots AR compitition. He uses an adjustable gas block. As he explained he opens the gas port one numbered drill size then installs the adjustable block. Closes the adjustment till near non cycle and shoots 5.56s and then increases the gas delivery till he gets proper function. Then he shoots 223s and increases then gas delivery in measured amounts till it functions proper. After that he indexes the two adjustment points so he can make on the spot adjustments for either round. He also uses the same weight bullet in each. His AR never fails. It is super smooth operating. Zero slam. Zero cycling issues.
All other things discussed are important too. Leaks, tube alignment, all of it. This the nature of auto loaders. Right charge. Bullet weight. Proper assembly and parts. If all is right in assembly and it shoots and cycles with 5.56 but not ,223 then the setup is for 5.56. A lighter spring will allow it to shoot 223 but there may be issues happening like bolt recoil slam with 5.56. a heavier bullet in the 223 might make it work without changing spring and allow a bit lighter bullet in 5.56 work as well.

 

[Varminterror]

As he explained he opens the gas port one numbered drill size

This should be your indicator to find a new advisor.

Ream. Don’t drill.

(The second indicator is his advice in 5.56 vs. 223rem ammo... my eyes rolled so hard I could see my brain...)

 

[BreechFace]

Ream. Don’t drill.

Technically speaking:

Drill = New hole
Bore = Enlarge an existing hole
Ream = Finishing/smoothing sides in an existing hole

Anyways, carry on.

 

[mcb]

This should be your indicator to find a new advisor.

Ream. Don’t drill.

(The second indicator is his advice in 5.56 vs. 223rem ammo... my eyes rolled so hard I could see my brain...)

Why ream this hole? I would bet most of the manufactures out there are not reaming this hole in a production setting. The tolerances don't require it to be that precise and nothing in it function needs that good of surface finish. The surface finish is gone after the first magazine.

ETA: A carbide drill is nice especially if the barrel is FNC'ed as it will stay sharp better breaking through that very thin but very hard coating but if you only doing it once a standard HHS drill bit will get the job done fine.

 

[skeeterfogger]

This should be your indicator to find a new advisor.

Ream. Don’t drill.

(The second indicator is his advice in 5.56 vs. 223rem ammo... my eyes rolled so hard I could see my brain...)

First of all I never said to drill.
Ok I may have got the 5.56 and ,223 backwards but any one with a brain could figure that. But the your eye roll viewed pure cavity.

 

[Varminterror]

Folks experienced in building (and fixing poorly built) AR’s will have experienced the difference in drilling vs. reaming to open an undersized gas port. If you like throwing burrs into your bore and causing copper fouling, it’s your rifle, but the proper tool for the job isn’t a drill bit.

His buddy was trying to sound smart by devising some complicated yet seemingly logical procedure - in reality, it’s simply not that complicated, but it sounded smart enough to fool the inexperienced.

 

[mcb]

Folks experienced in building (and fixing poorly built) AR’s will have experienced the difference in drilling vs. reaming to open an undersized gas port. If you like throwing burrs into your bore and causing copper fouling, it’s your rifle, but the proper tool for the job isn’t a drill bit.

His buddy was trying to sound smart by devising some complicated yet seemingly logical procedure - in reality, it’s simply not that complicated, but it sounded smart enough to fool the inexperienced.

Good sharp drill bits fed at the correct rate will not leave a burr on the interior especially if you are simply opening up an existing gas port a few thousands of an inch. I have done it many times with a drill bit and accuracy has not suffered. And even worst case and you do leave a minor burr 100rds later the burr is gone. If you got the reamer use it, it certainly will not hurt anything but if all you have is a number index of drill bits I would not go out and buy a reamer for fixing one barrel. Use good lubrication and a good vice on a drill press or milling machine and you will be just fine.