Normal Gas Port ????

Is this a normal looking gas port hole???





I am not familiar with gasgun ports, but this hole appears to be far too big - stretching across the entire width of a groove and even onto a land?

I have been struggling with load development with this barrel from a well-known and highly respected barrel-maker. This is a .224 6.5T 4-groove barrel, and has had at least 500 rounds through it.

(Apologies for the image quality - this is a $24.95 borescope.)

How big is the gas port? I know a lot of barrel makers go large so their customers can use whatever ammo they want. Adding an adjustable gas block is one answer if the gas port is too big. There's also custom inserts that can be installed in the gas block to restrict flow. If you want to shoot both with and without a suppressor, an adjustable gas block is the way to go.

What is your concern? Are you having poor functioning or poor accuracy?

The issue is attaining acceptable precision.
Something is not right with this rifle.

If you look closely at the second image in the post above, a small fiber of cleaning patch has snagged on a burr of some sort. In a later image (below) the fiber is gone but the hole still appears quite large. The hole in the top of the barrel seemed normal on the outside.



Does anyone have any first hand experience with viewing a gas hole/port from the inside with a borescope?

You need a right angle mirror

Not necessarily this exact one, but you get the idea
https://www.amazon.com/Yunanwa-Supereyes-Borescope-degrees-Endoscope/dp/B00CBKFJ9Y

Is that twist rate right? 1 turn in 6.5" What are you shooting with this?

Figure out the diameter of the gas port hole and then determine how that compares with the land/ groove diameter of the barrel. This is one reason why it may intrude on a land. The barrel maker should have drilled the hole undersized and then reamed it to final dimension to avoid burrs. Maybe it wasn't reamed at all or with a worn/wrong tool resulting in a burr. This could also be the case intentionally so the fitter could final ream to a diameter appropriate for the rest of the build. A longer than average barrel here may be your friend if the port was intentionally left undersized.

You can sometimes but not always remove a burr by, lapping a small diameter hole with a cast iron lap and fitting flour, ream with the correct diameter tool to remove the burr. ( maybe your gas port was never drilled to the correct diameter to begin with and your in luck) Use a tight fitting bronze bore brush and hope for the best, shoot it a whole bunch more or......now get this...... polish the bore ever so carefully with a threaded jag comprised of a number of small diameter leather washers separated with brass washers and a tiny nut to compress the washers intermittently using olive oil as a vehicle and flitz or JB paste to brighten it up only, then keep shooting.

After you have explored other methods first of course and while using a ball bearing clearing rod and a bore guide. The idea here is to polish and not an attempt to increase internal dimensions.

Always inspect barrels thoroughly before installation, that's when you want to send them back so you don't run into problems and go through all the work during installation and tear down.

Good luck with your rifle I'm sure you'll get it ironed out with a little more detective work and more suggestions for problem solving.

KRC said:

Is this a normal looking gas port hole???

I am not familiar with gasgun ports, but this hole appears to be far too big - stretching across the entire width of a groove and even onto a land?

I have been struggling with load development with this barrel from a well-known and highly respected barrel-maker. This is a .224 6.5T 4-groove barrel, and has had at least 500 rounds through it.

(Apologies for the image quality - this is a $24.95 borescope.)

Click to expand...

What is the length of the barrel and caliber? I have notes somewhere from a barrel build class I took several years ago. We all wrote the calibers and lengths of barrels we were building, along with the port sizes.

We drilled an undersized port and opened them up in increments until the bolt locked back on the last round.

I'll see if I can find the notes.

Thanks all for the informative responses.

Additional information:
- it is a 6.5T, as stated earlier
- the rifle is already fitted with an adjustable gas block
- feeding/ejection is 100% - no issues, as stated earlier
- a cheesy 45degree mirror has been ordered, but it will not likely fit down a .224 bore
- from both measured and calculated readings, groove width is about .132".
- from the images, it appears that the hole is the full width of a groove
- There is NO way a gas port should be this large???
(Certainly I would have noticed this during assembly if the port was this size on the outside of the barrel.)

While I appreciate the detailed information on correcting a burr issue with lapping instructions etc., I will not be attempting this. This is a $500 barrel that was ordered chambered and drilled from one of the most respected names in high-end barrels. If I am able to determine this is an issue it will be discussed with the vendor and the barrel will go back to them if necessary.

The question remains - is this normal or not normal???
It is possible that this burr/abnormal hole is damaging bullets as they pass, leading to inconsistent precision.

I've heard of a 6.5 Creedmore and Grendel, I'm not sure what a 6.5T is?

What weight bullet are you shooting? What is the twist rate of the barrel? Handloads or factory ammo? Has the headspace on the rifle been checked? Those things could be causing your accuracy issues and, in my opinion, probably more likely than a burr or size of the gas port.

Odds are none of us can tell if the gas port size is too big just by looking at it. It would have to be measured out.

6.5 is the twist rate. he said .224 so guessing 224 valk is the caliber.

have you tried any factory loads, what did you use and what groups are you seeing, any correlation to bullet weight?

The burr is supposed to go away after you've shot it.

The only way to measure the gas port properly is to remove the gas block and check with pin gages. The tail of a drill bit can also get you in the ballpark.

6.5T is a TWIST rate.
Chambering 224 Valkyrie.
High quality components have been used in the build.
Upper was lapped prior to barrel installation.
Bullets have been 77SMK, 77TMK, Berger 90 VLD, 88 Hornady ELD-M, 90 SMK. Powders have been 2000MR, H4895, Varget, H4350. Seating depths have varied from very 2.260" to 2.340" (cut window mag). Headspace is fine. Other variables for loading, rifle system and shooting platform have been investigated.

The barrel shows signs of promise (100 yard 5-shots within .250"), but is excruciatingly inconsistent, and 1/2" groups cannot be repeated, with flyers occurring.

Please, no more tangential questions.
While I appreciate the thoughts, I would just like an informed opinion as to whether or not this internal gas port hole appears normal or not from someone who knows the AR platform.
It looks considerably different than my other two AR's, and the burr can be felt with a tight patch.
If this expertise does not exist on this forum, that's A-OK - I recognize it's not a question most shooters will have experience with.

FYI - I am a very experienced shooter and handloader, and have investigated numerous other potential issues with this rifle before this. I am skeptical that this is the issue, but at this point it needs attention.

Only 5 factory rounds. 75 gr. Federal. 2" group. No love there.

There does seem to be a slight correlation with bullet size, with the 77SMK's the most consistent.
But that's not what the 224V is "designed" to do.
I use quotations around the term "designed" as I am NOT impressed with this chambering, and the (lack of) R&D effort on the part of Federal for this cartridge - but that's another matter.

Gas port size should have no affect on accuracy. Pressurization, yes. Accuracy no.

The gas port hole being drilled in lands and grooves will not affect accuracy either.

I you aren't happy with the burr, send it back.