Build Thread Gas issues on a new build

[Roymil666]

As soon as I get the build back into my hands I'll swap a few things and see where I'm at. Hopefully it'll be as easy as swapping the bcg or buffer. But I'll keep you guys posted. Thanks for the help.

 

[matts]

Run it wet, I've seen plenty of guys think it's so cool to have spotless dry ar15 because they want to be meticulous/particular, synthetic engine oil, drip little bit here and there , then rack the action on it a few times, then wipe off the excess.
I've " fixed " a few of my friends ar15 rifles this way.

 

[DirectDrive]

Now that I'm thinking about it; it may not have locked back every time.

That's a big clue right there along with the carbine spring and buffer "helping".
Gotta check and verify that the gas system is correct and clear.

 

[Member 34319]

Mid length 16" barrels can be undergassed at times, at least in my experiences with them, especially compared to carbine gas length 16" barrels. They tend to be much softer shooting too, because of the slower bolt speeds due to less dwell and lower pressure gasses. Failure to feed and failure to eject are common with longer gas systems on shorter barrels. You'll need one or more of; operating gas via larger port, less reciprocating mass via lighter buffer/spring/carrier, less friction via good lubrication.

If I had to guess which of the components on your list might be the issue, it would be the captured H2 spring set up. Likely too much spring and weight. A carbine buffer and regular spring would be a good start, which ir sounds like you've done. I pretty much always start with a regular spring and carbine buffer with any new build. If it is cycling too fast, then I'll go H2 or heavier in combination with a stronger spring.

Ive got a BA Hanson 16" midlength barrel on one of mine. It took a few mags to get going smoothly, but I did notice it is anemic in terms of gas. IE it is silly soft shooting and I imagine very close to short stroking. I run a semi auto BCG and a regular spring and carbine buffer. Swapping to the semi carrier (slightly lighter than FA) seemed to do the trick. It is dead nuts reliable suppressed, but I wouldn't trust it without the can to always cycle with how soft it shoots. If it wasn't such a nice barrel, I'd likely open up the gas port a bit. I still might.

 

[powermad]

Faxon has an interesting way to set gas port size.

Faxon created their gas port diameters by testing using a standard carbine. Specifically, we used a dry manganese phosphate carrier, an H2 buffer, and a military-specification spring. We then test-fired the weapon to ensure that it locked back with no lubrication and opened the port a bit further to account for adverse conditions.

The port on my Faxon 16" mid is .081"
Will be trying it out this weekend.
I'm using an A5 action with the A5H2 buffer to start with and have an H4 if that's not enough.

 

[v0lcom13sn0w]

i didnt go thru every post but if you havent yet, use a pin gauge to measure the gas port. ive had to open up a couple BA barrels

 

[HB of CJ]

Same answers. If you can and are equipped to do so, knock out the taper pins, slide hammer off the front site base and use either a precision drill bit size or a slug gauge and determine your exact existing gas port diameter. Fun quick and easy if you got the tools to do it with.

Shiet happens. Once had a brand new Colt HBAR AR15A2 with no gas port at all. Yikes.

 

[Roymil666]

So here's the update:
During his camping trip shooting "Federal Urban Tactical 55gr" he got it to cycle ZERO times with two separate magazines. I pulled it apart and checked the gas port with precision drill bits I snagged from work. The 1/16 .0625 would barely slip into the port the 5/64 .0781 was not even close. I drilled out the port using that bit and reassembled the rifle.

I'm taking it to the range tomorrow morning and will try it with 4 types of ammo, 2 separate bcgs (one NiB and the other a nitride C158), and using the standard Carbine spring/buffer as well as the Armaspec H2. I'll probably bring along one of my known reliable builds as well and interchange parts if I still can't get it to run.

 

[v0lcom13sn0w]

it'll prob run fine after drilling the port

 

[P7M13]

Drill out gas port works. Just make sure you have no burrs in the barrel - they can be folded back into the gas port hole and restrict it again. Figure you already know this if you borrowed bits from work.
I've also adjusted my buffer weight by disassembling it and removing the tungsten disks, replacing them with much lighter mass washers. Note, the space inside the buffer allowing "slop" between the disks is on purpose. Keep that space.
Also had a PSA that wouldn't cycle properly on occasion. Turned out the gas block was not properly anchored.

 

[Roymil666]

After range update:

I ran 10rnds of AE 55gr with C158 BCG w/ Carbine buffer/Spring and it ran perfectly. Swapped out to the H2 and ran another 10rnds perfectly. It's actually a little over-gassed now I would say. I ran a mixed mag of AE 55gr, PMC 55gr, Fed 62gr, and super old Norinco 55gr. Not one hiccup.

I forgot to try the NiB BCG but my buddy prefers the nitride one anyways.

Thanks for all the help and suggestions.

 

[titsonritz]

The 1/16 .0625 would barely slip into the port the 5/64 .0781 was not even close.

FYI, .0625 is correct size for a carbine length gas system and is too small for mid-length. .0781 is on the larger end of the range for a mid-length.

 

[Roymil666]

It is a mid length system. And I went with that .0781 to ensure reliability even with under powdered loads. I'd rather it overgas and adjust the buffer weight or an adjustable gas block then have it not cycle. It was ejecting with an h2 at about 2:30.

 

[DirectDrive]

After range update:

I ran 10rnds of AE 55gr with C158 BCG w/ Carbine buffer/Spring and it ran perfectly. Swapped out to the H2 and ran another 10rnds perfectly. It's actually a little over-gassed now I would say. I ran a mixed mag of AE 55gr, PMC 55gr, Fed 62gr, and super old Norinco 55gr. Not one hiccup.

I forgot to try the NiB BCG but my buddy prefers the nitride one anyways.

Thanks for all the help and suggestions.

Well done !
You were under-sized for a 16" Middy.
Never "drill out the gas port" without knowing what you are doing.

 

[Roymil666]

I took the range that @titsonritz (much thanks) posted in this thread and found a drill bit that was closest to the bigger end without going over. It was ejecting about 1:30 with a Carbine Buffer and then closer to optimal ejection range with the h2. Every round cycled flawlessly and it locked back every last round. Plus I was able to get silver dollar 5rnd groups at 50yrds. I'm fairly confident that this build will run great now regardless of ammo.

 

[Cerberus Group]

Install a Blue Sprinco spring...that will help as well.

Folks tend to go to the buffer first, but some times the spring that's being used can't handle the additional weight very well.