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Issues with new 308 build


AKDan
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I am new to the ar10 world and just completed my first build (I have built ar15s before and ignorantly assumed it would be just as easy) - not happy with its performance. I used a Wilson combat 16” recon barrel with intermediate gas system(I have one of their intermediate gas tubes), FailZero BCG, and OdinWorks adjustable gas block. The buffer system isn’t anything special - it’s the rifle buffer system that Aero Precision sells. The rifle won’t cycle without a suppressor on it, and launches brass at about 1 o’clock with a suppressor attached - the brass also comes out super dirty (not sure what that would indicate). It is only shooting about 1.5 MOA and has very odd, sluggish recoil. I have the gas block adjusted full open and am using good quality factory ammo. 
Does anyone have any suggestions? My level of knowledge on the more technical aspects of these guns is severely lacking. I have been advised to drill out my gas port but want to make sure that’s necessary before doing anything that drastic.

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Welcome to the forum.

There is some more info that will be needed to diagnose your problem.  Visit this thread and get as much of the information as possible.

You may need to drill your gas port, but there other things to look at as well. 

A rifle buffer should be OK for length and weight.  Few companies mess that up.

A couple of questions to start though.  How many rounds do you have downrange with the rifle?  How much lube did you use?

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36 minutes ago, AKDan said:

brass also comes out super dirty (not sure what that would indicate)

Expect that with a suppressor, I've seen it all my rifles, including a Sig piston gun.

You'll want to give it a few boxes of shells to mate up with opposing parts and get a carbon seal on the gas system. These large frames often start out sluggish but break in fine. Worst case you might have to open the port a bit, no big deal if needed.

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46 minutes ago, Armed Eye Doc said:

many rounds do you have downrange with the rifle?  How much lube did you use?

Only about 50 rounds through it so far. Lubed it up really well with Remington oil. How many rounds does it take to break in? Never had to really break in my other rifles.

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3 hours ago, AKDan said:

The buffer system isn’t anything special - it’s the rifle buffer system that Aero Precision sells. The rifle won’t cycle without a suppressor on it,

This right here tells you the gas port is too small.  Running the gas block wide open and it still does this is another indicator that the gas port is too small.

Your buffer weight is correct.  Your gas port isn't getting the energy there, because it's choking the system, and can't. 

Measure your gas port diameter and report back.  This new intermediate gas system on their 16" barrels is something new, with that 13" + gas tube.  Tell me what your gas port diameter is, and I'll figure out something else that will work, and get your gun running. 

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Ok here is the info from the water boarding post:

Buffer weight: 5.36 oz

Buffer length: 5.29 in

Buffer tube internal depth: 9.75 in

Buffer spring specs: Aero Precision, 12.625 in, 39 coils, silver

Wilson Combat intermediate gas system

Gas tube length: 13.25 in

Photos of bolt face and looking into magwell 

41C9B60A-C873-4304-8CA2-C7E059A3DA2A.thumb.jpeg.627c871d9d93a1a51471db31ead693c8.jpeg

8B41C611-2A59-46CE-A378-85858D1EE34E.thumb.jpeg.7fe5fbfdd708084cec4186cf7c42e083.jpeg
Wasn’t sure where to measure the clearance at ears and bolt stop so here are pictures EFC4E02A-1618-44BA-90B7-8E0F83D337DF.thumb.jpeg.c3f6b95d90450505e9cebc27dcdbb07e.jpegE39DD6EA-4B17-4168-8220-4FA12EAC550D.thumb.jpeg.b0d634437a68d6f495e440dcb91b682e.jpeg

Gas journal: .75 in

Gas port: .078 in

22 hours ago, 98Z5V said:

what exactly is it doing, when you shoot it with no suppressor on it?

It either doesn’t cycle at all or it stove-pipes.

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Gas tube length is good, recoil systems is goor, except for maybe the spring.  Armalite EA-1095 spring or Sprinco Red spring will definitely do it.

All that's left is gas port diameter.  With the proper gas port diameter, that gun will run.  Like a sewing machine.

Let me look at one that I have that's similar, check it's gas port diameter.  I'll tell you now, this I know...  18" midlength gas, 0.750 journal, needs 0.085" port.  16" midlength gas, 0.750" journal, needs closer to 0.090" port.  With your  longer-than-midlength gas tube, you can come down a little from there, but I'll say you need 0.085" port, minimum.  Maybe a little more. 

That gas port needs to be drilled out.  0.078" just isn't enough. 

Edited by 98Z5V
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23 hours ago, Albroswift said:

one thing I notice in the photo it looks like the bolt face barely clears the bolt stop.

There's two reasons for that in the measurements he gave:

 

On 9/27/2022 at 5:51 PM, AKDan said:

Buffer length: 5.29 in

Buffer tube internal depth: 9.75 in

 

Buffer should be 5.200" long, and his is 0.090" longer than that.  Rifle Receiver Extensions should be 9 11/16 internal depth, and he's 9.75" internal (9 12/16) (1 16 = 0.063"). 

Overall, his recoil system hard parts are 0.027" too long, combined.  Not enough to make an operational difference, when most proper clearances give you 3/16" ckearance between the bolt face, with BCG all the way back, and the bolt catch.  Not perfect parts, but they should be working.

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  • 3 weeks later...

Hi all,

I’m back after making the changes: drilled the gas port to .085 and installed EA-1095 buffer spring. Tested the gun and it ejects about 2 o’clock suppressed and about 4 o’clock un-suppressed. It feels a lot more crisp and normal. Had one malfunction in the 20 rounds I shot (besides when I was testing how far I could close the gas block and the gun still function), but I was using cheap ammo so maybe that was why. Also, it’s not really broken in yet. Shooting about 1.5 MOA with cheap factory ammo, so I’m pretty happy. Thanks for the help!

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