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Swallowing pride, asking for help (after reading the numerous threads on the subject)


308USK
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I've built my rifle and it "should" work just grand.  But it isn't cycling...(note: I can manually cycle rounds from the mag [safety on] without issue).  GRRRRR

My build:
Aero Precision M5 Upper & Lower
Aero Precision 18" .308 CMV Barrel, Rifle Length
Rifle length gas-tube (from Aero Precision)
Superlative Arms Adjustable Gas Block (.750 Low Profile)
Magpul Enhanced Receiver Extension (7-3/4" internal length)
JP Rifles Silent Capture Spring (JP SCS2-10)
Aero Precision .308 BCG (black nitride)

I do wonder if my gas tube is 1/16 to 1/8" too long (see attach pics).  I've tried a number of things to troubleshoot, but feel it is time to 'go back to basics (get the rifle built to normal specs, working properly...then fine-tune with things like JP SCS, etc.).

That said, I need to order a proper buffer spring and buffer weight, which is where I need y'alls help.  I have read a bazillion threads, know that the AR-10 platform typically needs a 5.40z buffer weight and a proper spring.  

Saw a thread where that info was posted, but cannot find it for the life of me.  Once I get the info needed, I will order a spring and weight, get those put in the rifle and go to the range to see if that will have the rifle cycle.

I'm feeling pretty dumb right now, but know that y'all will have the knowledge to help me get my rifle right and working!!

Thanks in advance!

- -
Pete

 

Buffer_Tube_internal-length_x40.jpg

Gas-Tube_Close_x40.jpg

Gas-Tube_Mag-well_x40.jpg

Edited by 308USK
updated info for clarity
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Your gas tube is fine  -leave it in there.  You have a known, verified, high quality receiver extension.  You can use any AR15 Carbine buffer that is H3 weighted - it'll be 3.250" long, and that's what you need for that extension, but makes sure it's H3 weighted - that's the 5.4oz buffer.  You need one of two springs, either the Armalite EA1095 spring, or a Sprinco Red spring - either one will do the job, admirably.

On that barrel profile, you must have a gas port diameter that's 0.096", or very, very damn close.

Fix those things, and that gun will eat any ammo you throw at it.

Always start the gas block Wide Open.  Wide open.  After the gun runs right, and it broken in, then you can start dialing it down to your desired recoil, and functional level.

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29 minutes ago, 308USK said:

Aero Precision 18" .308 CMV Barrel, Rifle Length
Rifle length gas-tube (from Aero Precision)

It's good to see this in there, stated, with the pics you posted.  At least AP is catching on that the AR15 rifle gas tubes are too short, and they've included/sold a gas tube that's probably 15.5" (the Armalite AR-10 rifle gas tube).  I'm glad to see the realization, in their part, and fix that.

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13 minutes ago, 98Z5V said:

Your gas tube is fine  -leave it in there.  You have a known, verified, high quality receiver extension.  You can use any AR15 Carbine buffer that is H3 weighted - it'll be 3.250" long, and that's what you need for that extension, but makes sure it's H3 weighted - that's the 5.4oz buffer.  You need one of two springs, either the Armalite EA1095 spring, or a Sprinco Red spring - either one will do the job, admirably.

On that barrel profile, you must have a gas port diameter that's 0.096", or very, very damn close.

Fix those things, and that gun will eat any ammo you throw at it.

Always start the gas block Wide Open.  Wide open.  After the gun runs right, and it broken in, then you can start dialing it down to your desired recoil, and functional level.

Copy on leaving gas tube alone!

Will locate a proper Carbine buffer @ H3 weighted and 3.250" long.
Will locate either of those buffer springs.

As for gas port diameter, I may have to disassemble and use the #'d bit method I read in one of the many posts to ensure proper diameter.

Once I get pieces-parts and check gas port diameter, I will go to the range, open the AGB wide open and give the rifle a whirl. :)

THANK YOU!!

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@98Z5V and everyone else

update:

Got the new spring & buffer weight in last Friday; got 'em installed yesterday.  Lubed up the BCG during re-assembly.

Went to the range today, to see what changes, if any, would come (also opened up the gas block all the way).

No changes.  :'(

I have also looked at the specs on Aero Precision's site, for the barrel I have.  I believe the gas port is NOT big enough (dammit).  That said...probably need a #42 bit, correct??  Best place to acquire?

AP_18inch-308-BBL.jpg

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Posted (edited)
13 minutes ago, dpete said:

Any good hardware store will have numbered drill bits that will do the job.  A  #42 or more likely a #41

I know just the place (my Dad called it the 'toy store' when I was growing up).  :P

I'll make a trip to the toy store and buy both a #42 & #41 (possibly a few in the range, for sizing before drilling).  Thank you for the reply!!

FWIW, I'm a little surprised that AP makes barrels that are not properly sized for their gas port (just looked at the 20" .308 barrel and it's gas port is also .0890" (facepalm).

Edited by 308USK
update info
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On 7/24/2022 at 6:07 PM, 98Z5V said:

Your gas tube is fine  -leave it in there.  You have a known, verified, high quality receiver extension.  You can use any AR15 Carbine buffer that is H3 weighted - it'll be 3.250" long, and that's what you need for that extension, but makes sure it's H3 weighted - that's the 5.4oz buffer.  You need one of two springs, either the Armalite EA1095 spring, or a Sprinco Red spring - either one will do the job, admirably.

On that barrel profile, you must have a gas port diameter that's 0.096", or very, very damn close.

Fix those things, and that gun will eat any ammo you throw at it.

Always start the gas block Wide Open.  Wide open.  After the gun runs right, and it broken in, then you can start dialing it down to your desired recoil, and functional level.

98 gave you the gas port size a while back.  The man is the Guru of gas port sizes for barrel lengths. 

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1 hour ago, 308USK said:

I know just the place (my Dad called it the 'toy store' when I was growing up).  😛

I'll make a trip to the toy store and buy both a #42 & #41 (possibly a few in the range, for sizing before drilling).  Thank you for the reply!!

FWIW, I'm a little surprised that AP makes barrels that are not properly sized for their gas port (just looked at the 20" .308 barrel and it's gas port is also .0890" (facepalm).

They make the gas port small so they can try to cheat and make the recoil system buffer lighter than its supposed to be.  Cost saving measures that cause rifles not to function and customers to come here to get said rifles fixed and working.

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8 hours ago, dpete said:

98 gave you the gas port size a while back.  The man is the Guru of gas port sizes for barrel lengths. 

Yep, I have that 411 bookmarked, as well as in a Note pinned to my tablet, so the info is always readily acceptable.!!! :)

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So...update #2:

Started taking the rifle apart, so that I could drill out the gas port, as the rifle was still not cycling after installing 'factory' spring & buffer.

Interesting development as I was taking the gas block off; the gas tube came OUT of the gas block, despite the PIN being in the block and I am 2,000% certain the gas tube was properly pinned as both myself and my brother checked it after setting the roll pin.  I took a couple pics of the roll pin; it seems to be 'okay' though I am considering replacing, just to be safe.

Now for the even MORE interesting part:

Took my digital caliper and measured the gas port, 3 times.  The attached pic shows the measurement I got 2 of the 3 times.

 

SO...now, the questions are:

  1. Do I re-use the gas tube or buy a new gas tube?
     
  2. Re-install gas tube (ensuring the tube is pinned) > re-install the gas block > open gas block up wide open > go to range and put 3-5 rounds down-range?
     
  3.  Drill out gas port even though the gas tube was not pinned, as we all know that for an 18" rifle-length barrel, the gas port needs to be 0.090" -> 0.096"
     

Rather than blast through this and just drill baby drill, I felt it wise to consult the community of knowledge first!  Thanks in advance

- -
Pete
aka 308USK

IMG_0051-30.jpg

IMG_0052-30.jpg

IMG_0054-30.jpg

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19 minutes ago, 308USK said:

Re-install gas tube (ensuring the tube is pinned) > re-install the gas block > open gas block up wide open > go to range and put 3-5 rounds down-range?

As long as the tube isn't damaged this^.

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18 minutes ago, jtallen83 said:

As long as the tube isn't damaged this^.

Thanks Brother!

I'll proceed down this path.  I did, just for sanity sake, order a couple of Armalite Rifle Length gas tubes (never hurts to have spare parts).

Will re-assemble, slow-n-steady, open up the gas block and head to the range for 3-5 rounds down-range to check rifle cycling.

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That gas port is still too small, at 0.0835" measured.  It will HAVE to be bigger.  Get it in the range you'll need, before you put it back together.  If you can get that pin back in there, and that gas tube isn't damaged, like Jim said, then run it.  :thumbup:

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15 minutes ago, 98Z5V said:

That gas port is still too small, at 0.0835" measured.  It will HAVE to be bigger.  Get it in the range you'll need, before you put it back together.  If you can get that pin back in there, and that gas tube isn't damaged, like Jim said, then run it.  :thumbup:

Yeah...that gas port is just bugging my brain!  The more I think about that, the more I think I may drill to #42 and re-assemble, take to the range and see how it cycles.  Not difficult to disassemble and go a wee-bit more with the #41, should it cycle but not great.  Plus, I can always drill out to #41 and install new Armalite Rifle Length gas tube once it comes in, to be 100% certain things are squared away.

 

IMG_0056.jpeg

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9 hours ago, 98Z5V said:

Punch it up, man.  If it was mine, I would, with zero hesitation.  Drill baby, Drill!   :hail:

Palin Drill Baby

LMAO

Drill baby drill to take place after working hours today...

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Post DRILL BABY DRILL update (LOL)

Got prepared by using a toothpick and measuring from outside top of barrel to bottom inside of barrel, marking the toothpic at the top of barrel.  Then took that and halved the distance (for safety measures) and taped the drill bit at the 1/2 length to prevent going any further.  Started to drill the gas port using the #42 bit with my cordless drill/screwdriver, got a little ways in and the battery croaked.  Zipped over to Lowe's (5 min away) and bought a corded drill (military discount helps some).

Got back, re-started drilling...slowly and methodically.  After just a few minutes, I was through and had NOT touched the inside bottom of the barrel at all. :)

Went back in the house and ran my Bore Snake with CLP through the barrel 3x.

Before I re-assembled, I used some canned air to blow through the gas tube.  I then started the process of re-assembling.  As I put the gas tub into the gas block, I watch VERY CLOSELY for the end of the tube, then the roll-pin hole.  Once that was properly aligned, I used a pin punch to go through the hole and check the alignment inside the upper (see post drill-out of gas port pic).  As I look at the Pre drill-out of gas port pic, I do think that the gas tube was not properly set in the gas block!!  Once the gas tube and block were pinned and set, I once again used canned air (AGB wide open) and was able to feel air coming out the muzzle end!

That said, I also believe the gas port was NOT the correct size from the factory.  Using the #42 bit, I now have a gas port that is 0.0945" (see pic).

Have completed the re-assembly, ensured the BCG was well lubed and AGB wide open, I will go to the range tomorrow after work and run 3-5 rounds through the rifle to check cycling.

Once I have a rifle that properly cycles, I can begin the process of fine-tuning.  :)

Again, I totally appreciate the knowledge and advice from y'all!  Further update(s) after the range tomorrow!

 

Gas-Tube_Close.jpeg

Gas-Tube-Post#42Drill-Out.jpeg

Post-#42Drill-Out.jpeg

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