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Remember to CLEAR THE GAS HOLE !.


BushXM15
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Yeah well when installing a gas block take the time to ensure the Gas Hole and the Gas Block's HOLES ARE CLEAR  ; BEFORE ASSEMBLING :facepalm:

 

Yep function test failed immediately  and I knew they were aligned properly ,so like a dumb azz  I immediately think SPRING . NOPE !.

 

Long of it short  I finally pulled the compensator ,gas block and looked into the barrel gas hole ( With a light down the inside of the barrel no less )  HOLE was DARK :thumbdown:

 

Sure enough there was CRUD as IF the barrel had been polished and NOT properly cleaned before it came too ME .  You learn something every time or at least I do !. :ack:

 

CHECK EVERYTHING BEFORE ASSEMBLY IT SAVES FRUSTRATION . I felt like an idiot hand charging those #5 rounds :tap: 

 

 

ALL functions perfectly NOW :thumbs2:

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Bush I've had them with burrs hanging down and a round will push it up and block the hole.  I always run a patch through my bores when I get them. If one is there I'll get it out with a tight patch catching it. After that a shot will take out any slight edge lefet.

 

Greg

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On 11/25/2022 at 6:52 PM, Tiribulus said:

Not that I'm in any way doubting what you're saying, but what kind of crud did you have in there that could withstand all that pressure?

 

It was grey/white what appeared to be polishing compound but the hole was steadfastly plugged and I mean HARD Plugged .  I ended up taking an 0.0890 bit #43 wire size and cleaning the gas port ,it was pretty close to the hole diameter . I've an adjustable gas block  so IF anything should be a Miss I'll dial on it first ,before Drilling gas port larger .

 

When I said all functions perfectly now ; That REMAINS to be seen . Rifle cycled #5 rounds and locked back on empty clip but that's hardly any conclusive endorsement at this point in time .  MY gas block system is Rifle length and NOT mid length . It's mounted with 9.5" of barrel left ,so 12.75" before the the gas block . Barrel actually turned out being 22.257" . As best as I could measure it !.

 

I have NO hand loaded rounds for it ,until I empty some Norma  Golden Target but am carefully proceeding as to break in instructions . I have a set of printed barrel break in procedures , from Two Spot on custom barrel manufactures and I use those anytime I shoot a New bore . Figure it can't hurt and probably is what should be done and if anyone knows they most certainly would . :thumb:

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If I break one in it's pretty simple, 5X1,5X2, 5X3 and then 3X5 shot groups.  Truth be known I don't break anything in now.  I strt from the get go shooting groups.  Most days I'll shoot 50 or 100 rounds on the first outing getting groups and speeds. YMMV

 

Greg

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1 hour ago, GLShooter said:

If I break one in it's pretty simple, 5X1,5X2, 5X3 and then 3X5 shot groups.  Truth be known I don't break anything in now.  I strt from the get go shooting groups.  Most days I'll shoot 50 or 100 rounds on the first outing getting groups and speeds. YMMV

 

Greg

But, pushing a patch through before you start with any new barrel is standard procedure. It's amazing how much crap some come with from the manufacturer, even top brands.

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On 11/26/2022 at 3:23 PM, Longhair said:

But, pushing a patch through before you start with any new barrel is standard procedure. It's amazing how much crap some come with from the manufacturer, even top brands.

 

I wish we all had a dollar for every Standard Practice that gets ignored. Some guys like to really strip em down with cleaners. One custom barrel company leaves a wax in the bore used when the button is pulled. I never clean that out and the barrels will sometimes shoot the best group of the day on the first five shots.

 

Greg

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On 11/26/2022 at 3:23 PM, Longhair said:

But, pushing a patch through before you start with any new barrel is standard procedure. It's amazing how much crap some come with from the manufacturer, even top brands.

 

Amen to that Brother ; Filthy dirty  is an understatement  from some manufacturers and WHY  :dontknow:.

 

MY personal consensus on  20" + Barrel  in 6.5 CM or .308  ,I'd make the port size  : 0.080-0.090" diameter . I've read where to many people tried 0.062" -0.070" and had cycling problems  . I agree with starting smaller IF YOU'RE the one drilling but I'd leave it up to the the barrel manufacturer and Tweak it " ONLY " if it became necessary . Nobody likes a finicky NON functional AR ,including ME 

 

I talked with a really close friend of mine last night and decided to ask him if he knew anything about port sizes . Well he didn't either but said he knew someone who more than likely did . So AM I received an Email from him  and # 3 things dictate port size .

 Length of Bore diameter of barrel  ,Powder burn rate ( Dwell time )  position of Port ,also running suppressed requires LESS gas and why it's advisable to use an adjustable gas block ,so as NOT to over cycle the bolt . You can correct it by using a heavier buffer ,stiffer spring and or adjustable gas block . He had NO definitive answer for Port sizes as per so many variables . However did agree with MY assessment above and stated a good # of manufactures use   0.082-0.085" as " Standards " as they can be enlarged IF necessary but generally need choking as more suppressors are purchased by AR owners .  

 

With less bore space and slower powders, your port pressure is higher.  Doesn't matter so much about peak pressure in the chamber because .308 and 6.5 CM have a 62ksi working pressure limit, but .308 has more bore space to dissipate pressure with a faster conversion rate.

 

Stands to reason when one figures a larger bore has more volume of gas ,so smaller opening makes sense  or does it  ?. Smaller bore less gas volume larger port opening but then come PRESSURES ,different calibers operate at 52K  62K psi also come into play .

Below is something  I borrowed , agree or Not ?

 

Ok. In general- Larger gas ports for systems with shorter dwell times.

Larger gas ports for longer systems because pressure is less.

Would it be safe to say that posts I've read in the past stating larger ports are needed because the gas system has been shortened are either A) not accurate or B) I mis-understood what was written?

14.5" barrels have the same amount of barrel past the gas port as 20" rifle gas barrels...by design.

Shorter barrels than 14.5" will require a larger port to allow the gas system to fill with gas before the bullet leaves the barrel because everything is going to happen faster than would be needed if there was more barrel beyond the gas port. This is why 11.5" barrels are generally more reliable than say 10.5" barrels. The gas system has more time to fill and begin operation before than bullet leaves the barrel vs. the same size gas system on a shorter barrel with less barrel after the port.

14.5" barrels call for a gas port of .062". Rifle gas systems I've seen vary from .090-.100". These are larger because the gas tube being longer causes the entire gas system to be of larger capacity and the gas pressure is lower since the port is further from the chamber....simple physics.

All FSBs and gas blocks should have the same size port. Gas volume and pressure is controlled by the length of the gas tube and the size of the gas port in the barrel.

 

  

The Gas Port

The gas system starts at the port, a small hole drilled directly into the barrel. The port allows gas produced inside the barrel to escape, to be vented into the gas block.

Gas Port Diameters

Gas port diameter simply measures how wide the gas port is on the barrel. A collection of measurements from different manufacturers and barrel makers illustrates that port diameters tend to fall within certain ranges. These are the most common ranges of diameters you'll find on AR-15 barrels measuring 11.5" to 24" in length. Port diameter also changes depending on the thickness of the barrel itself (0.625", 0.750", or 0.825"):

  • 11.5" Barrel (0.625") Port: 0.081" to 0.089"
  • 11.5" Barrel (0.750") Port: 0.086" to 0.094"
  • 14.5" Barrel (0.625") Port: 0.063" to 0.078"
  • 14.5" Barrel (0.750") Port: 0.070" to 0.086"
  • 16" Barrel (0.625") Port: 0.063" to 0.078"
  • 16" Barrel (0.750") Port: 0.070" to 0.086"
  • 20" Barrel (0.625") Port: 0.086" to 0.093"
  • 20" Barrel (0.750") Port: 0.093" to 0.096"
  • 24" Barrel (0.825") Port: 0.089"

A note about port diameters and performance: 

If you've already built an AR and are experiencing issues with the gas system (like over-gassing and excessive recoil or conversely, short strokes, failures to feed or cycle, or jams) it is strongly recommended you first attempt to replace the buffer with a lighter or heavier unit, followed by installing an adjustable gas block (discussed in the next section). Modifying the gas port diameter can have disastrous consequences, requiring a barrel swap. Because port diameters are often non-specific to barrel length and gas tube length as shown above, it is difficult to identify "the perfect diameter" for any one cartridge and setup.


The Gas Block

To safely handle the extreme heat and pressure of the gas being produced in the barrel, the gas block is made from forged, hardened steel. Most are coated with phosphate or nitride, though some are made from stainless steel to resist rust and corrosion. Gas blocks can take many different forms, each with their own features:

 

https://www.80-lower.com/80-lower-blog/builders-guide-to-ar15-gas-systems/

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1 hour ago, BushXM15 said:

 

<snip>
14.5" barrels call for a gas port of .062". Rifle gas systems I've seen vary from .090-.100". These are larger because the gas tube being longer causes the entire gas system to be of larger capacity and the gas pressure is lower since the port is further from the chamber....simple physics.<snip>

No longer true. Some manufacturers of 14.5" barrels are making them with mid-length gas systems, while others are making them with carbine-length systems.

 

I just bought a 14.5" Rosco Bloodline barrel, and part of the reason I selected it was the carbine-length system. I intend to run it suppressed the vast majority of the time, but I'm also incorporating an adjustable gas block. I'll dial it in with the lightest .223 loads that I'll use and lock it down where it cycles reliably. My goal isn't to have it shoot as softly as possible, but to have it cycle as reliably as possible. 

YMMV

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On 11/27/2022 at 3:29 PM, Longhair said:

No longer true. Some manufacturers of 14.5" barrels are making them with mid-length gas systems, while others are making them with carbine-length systems.

 

I just bought a 14.5" Rosco Bloodline barrel, and part of the reason I selected it was the carbine-length system. I intend to run it suppressed the vast majority of the time, but I'm also incorporating an adjustable gas block. I'll dial it in with the lightest .223 loads that I'll use and lock it down where it cycles reliably. My goal isn't to have it shoot as softly as possible, but to have it cycle as reliably as possible. 

YMMV

 

Everything down below the heavy type I borrowed and one thing I can absolutely tell you ; NO two people agree on a port diameter  regardless of system used .

I figure barrel manufacturers pretty much know their business and have tested XXXXXXXXX # of units ,so they KNOW what does and what doesn't work .

 It's not like there's the holy grail  of a magic  size , hence the variables .  One point everyone was in agreement with was , the THICKER barrels require larger Diameter ports .  I've often wondered how many AR shooters recognize over gassing ?, meaning if it's slinging brass and locking back on an empty Mag ,it's GOOD TOO GO .

Consider NON reloaders  as an example . M855 & M193 are gonna function Most AR15's  but maybe a generic inexpensive loading won't ?.

I personally have had ZERO issues with any of MY AR's ,save for this 6.5 CM but it was MY FAULT NOT CLEANING and inspecting it prior to assembly . MY BAD :thumbdown:

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Yep. No Holy Grail numbers. I run adjustable blocks on 90% of my AR's. Shooting everything from 17-223 to 458 SOCOM on a lower with standard buffer and springs. O can tune one in about five shots. I prefer to run BIG gas ports. I want lots of latitude and since I got a suppressor last year I do want that in spades. 

 

Greg

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On 11/27/2022 at 4:24 PM, GLShooter said:

Yep. No Holy Grail numbers. I run adjustable blocks on 90% of my AR's. Shooting everything from 17-223 to 458 SOCOM on a lower with standard buffer and springs. O can tune one in about five shots. I prefer to run BIG gas ports. I want lots of latitude and since I got a suppressor last year I do want that in spades. 

 

Greg

 

Well any more isn't it a must ?. I mean suppressed or open compensate r  , you need the gas but also regulatory control of that gas so as not to beat items up .

 

 

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On 11/29/2022 at 5:22 PM, BushXM15 said:

 

Well any more isn't it a must ?. I mean suppressed or open compensate r  , you need the gas but also regulatory control of that gas so as not to beat items up .

 

 

 

Lots of guys hate them. They are better than pockets in pants IMHO. I kinda think they are seeing more use in the world's military.  This is truly one place where we want gas regulation.

 

Greg

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