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Discussion Starter · #1 ·
Does anybody know if the grooves in a barrel are cut such that the gas port is always drilled on a land or groove?

Different twist rates, different groove counts, etc. must affect the outcome. Also, I would imagine that the groove cut must be oriented to the barrel's final indexing.

I know nothing of barrel manufacturing, so I'm hoping someone who does will help satisfy my curiosity.
 

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Krieger guarantees that they put them in the groove , problem is on an ar, the gas port is generally bigger than the groove.
However , latest bore scope observations among us in the highpower game conclude it's best to have the gas port half in a land and groove as those tend to erode less than the ones entirely in the groove. I have also found this to be true . Lastly, by the time you wear out a gas port enough to affect accuracy, the throat is generally gone anyway.
 

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Krieger guarantees that they put them in the groove , problem is on an ar, the gas port is generally bigger than the groove.
However , latest bore scope observations among us in the highpower game conclude it's best to have the gas port half in a land and groove as those tend to erode less than the ones entirely in the groove. I have also found this to be true . Lastly, by the time you wear out a gas port enough to affect accuracy, the throat is generally gone anyway.
I fully understand how that works with even land/groove barrels, but what about a odd number like 5R, just drill it and roll the dice?
 

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Since I just went through the 5R research myself, I discovered that the gas port is the cornerstone of how the barrel is made. Everything is referenced off the gas port location within a groove of the barrel rifling. Kreiger will not make a 5R barrel already cut for an M14/M1A. There are only four people I know of who will make a 5R barrel for us. Dave Sullivan, Mike Rock, Jon Wolfe and Steve(?) Satern. Dave uses Obermeyer semi-finished blanks.

Once the gas port location is identified within a groove at a given distance from what will eventually be the barrel threads, the hole is drilled. That now becomes the reference point for the rest of the machining steps like barrel/receiver thread origin, barrel shoulder, gas cylinder splines, threads and muzzle. Custom barrels cost a lot of money. Look at adding $700 to $1000 to have one of these barrels made, installed and having the rifle shipped back to you.

Dave Sullivan specs out your receiver ring and factors that into making the barrel. He literally machines them custom for your receiver so that the barrel times perfectly and the ORG, GC and FS are perfectly perpendicular. Because of this, you can't just have him make a barrel and ship it to you so you can build it yourself. I think that goes for the other makers of 5R barrels too; maybe not.

When Jon tells me my 5R barrel is ready, I'll send him my kit so he can build it and nitride the barrel.

Tony.
 

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Discussion Starter · #5 ·
Using the gas port as the datum point makes a lot of sense; the gas system, including the op rod/piston have to be located accurately for the whole thing to work.

I was surprised at the best location for erosion control was half land and half groove. I was thinking that the muzzle side of the gas port on such a port location would present a pretty sharp corner to catch the bullet as it passes by. I presume that the bullet deformation has already happened before the gas port is reached so no big deal.

The original question arose when I was trying to figure out why some barrels shoot better than others; the gas port location came to mind as a potential variable. Then, I wondered if any manufacturer actually controls where the lands/grooves meets the port.

At least Krieger does; I suppose there are others or would I be safe in assuming most barrel manufacturers do when making rifles with gas ports?
 

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From the original blueprints


To a machinist this specifies centering the port in a groove (with a 4R, 1:12 barrel) and it shows part of the info about how it relates to the other features of the barrel.
 

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I understand the concept of why gas port was in a groove, and gas ports having a 50/50 overlap aiding longevity...... Does it matter??? Gus has said a few times that the team ordered barrels from Barnett and that they added the G/P too make sure there was perfect alignment with the G/C..

Personally, I don't think it really matters as long as the barrel has a port too make it work......
 

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Well let me tell you guys cuz I've got all the scoop, I read on the Internet...yadda, yadda, yadda. DI5

I haven't got a clue but I hope there will be some more interesting info. I have no idea if it effects accuracy in any way but I can see why they felt that it would reduce port erosion. Whether it does or not I can't say.
 

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port erosion

Rammac brings up a good point, " Did they consider location of the gas port in terms of erosion"? If they did, the increasedd dia, of the different parts through which the gas passes would have been reversed.
 

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When I built my .300blk pistol I researched different barrels.

Some makers drill their gas ports with the same tools for all barrels they finnish. Despite different calibers "requiring" different gas port locations.

Taking into account all the variables:

Type of Rifle
Caliber
Twist rate
Type of rifling
Barrel length
Gas system type
(Di pistol/carbine/rifle)
(Short stroke / long stroke piston)
(adjustable / non adjustable)
Gas port diameter
Suppressor?

And the topic here gas port location in relation to the rifling. You can combine any other of these and likely some makers will pay more attention to To one or the other.


That's all I can think of. AFAIK about gas guns these variables affect functionality more than accuracy.

I would love to read more on this

Krieger states on their website that explains 5r that they can observe no difference in accuracy between their 5r and 4 barrells.
 

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Krieger states on their website that explains 5r that they can observe no difference in accuracy between their 5r and 4 barrells.
While true, you should see a velocity increase with the 5R contour due to the angle of the land cuts. It will be interesting to see how the Wolfe barrel performs with the 20 degree cut.

I can't remember where I read or talked about it, maybe with Phil McGrath, but the same load with a 5R barrel gains about 20 or 30 FPS compared to a similar barrel with the same barrel length and twist rate but with a 4 land cut instead. It should make for a more efficient round that will perform nicely at longer distances.

Tony.
 

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I wonder if the increased velocity is more the result of reduced frictional forces (less bore material with 5 grooves rather than 4) instead of contact angle.
 

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While true, you should see a velocity increase with the 5R contour due to the angle of the land cuts. It will be interesting to see how the Wolfe barrel performs with the 20 degree cut.

I can't remember where I read or talked about it, maybe with Phil McGrath, but the same load with a 5R barrel gains about 20 or 30 FPS compared to a similar barrel with the same barrel length and twist rate but with a 4 land cut instead. It should make for a more efficient round that will perform nicely at longer distances.

Tony.
I wonder if the increased velocity is more the result of reduced frictional forces (less bore material with 5 grooves rather than 4) instead of contact angle.
Yeh it was me, My thinking was and still is that with a 5R barrel the bullet swages into the bore with less pressure and less bullet jacket distortion thus it seals better, they don't waist energy so there is more energy too push the bullet down the bore. I was told long ago by a shooter that knew much more than I will ever know that 5R barrels doesn't pinch the bullet like even land and groove bores do, there reduced radius of the rifling didn't have the drag or friction that conventional rifling does.

Made sense too me then still does now...

Not too get off the subject of G/P in the lands or groove or 50/50, I was just throwing out the 5R as a bump in the road, curve ball. There isn't a lot room and your going too hit a land or a groove or some percentage of both with a odd bore. That's why I mentioned that the USMC team just drilled them and went about there way.

I think Me and Art are in the same camp, the rifle doesn't care. And as long as the rifle works the shooter shouldn't either. Personally I have never seen a barrel removed due to G/P erosion and still have good T/E-M/E numbers........
 
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sorry to keep asking about 5R, but why would velocity matter if accuracy doesnt change?

also you said 20-30 fps? does it go up exponentially depending on the length of the barrel? for example would a would an 22 inch 5r barrell see a 20fps gain over a 22inch reg. and then a 33 inch barrel see even more gain per inch than a regular 33incher?
 

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The location of the gas port, rather in the grove or lands of a M14 or M1A makes zero difference in the accuracy of that barrel.. Much to do about nothing, I have my ear plugs in awaiting the blast... . Art
As much as I would like to argue with Art, I have to agree with him on this one. I've gone through a few barrels over the years in both 223 and 308, I could not see any difference in precision relative to the GP location. The barrel performance is more dependent on how the chamber is cut relative to the center bore of the barrel. AKAJUN, one of our own here chambered a very inexpensive Green Mountain Barrel for me with 2 conditions; no flash hider and gas post NOT specified in the groove . His process in barrel preparation and chambering is consistent with most bench rest gunsmith practices, the $51.00 GM barrel he turned for me is probably as precise of a barrel I have ever had, if not the top. I have shot just about any major barrel brand out there over the years.

I shot this target at 200 yards with my short line ammo centering the scope as I prepared to do load work for my long range ammo. 2 cold bore shots, clicked and adjusted then adjusted for the middle. At that point I quit and proceeded to do my long line load work. Like I mentioned AKAJUN chambered this 51 dollars GM barrel and I have no idea where the gas port is located.


 

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sorry to keep asking about 5R, but why would velocity matter if accuracy doesnt change?
There are two schools of thought, if the velocity picks up I can cut back on the powder load getting a little economy in return. Or the Long Range shooter can load a little bit more too extend the rifles range without getting into overpressure.

also you said 20-30 fps? does it go up exponentially depending on the length of the barrel? for example would a 22 inch 5r barrell see a 20fps gain over a 22inch reg. and then a 33 inch barrel see even more gain per inch than a regular 33incher?
Yep, that's the idea. But nothing is guaranteed, all barrels are different. A free 20-40fps gain in a 22in barrel without adding any powder is a bonus in my book.
 

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Neither do I , I didn't care, the gas port on that barrel at .093 is way wider than than a groove anyway and almost half the diameter of the bore. There is no point in trying to put it in a groove as it's going to cut at least one land anyway.
In addition. , I have bore scoped a bunch of service rifle barrels , kriegers with them in the groove , others not. As what most hp shooters have found , the ones that split a land and groove seem to erode less than one entirely in a groove , the location does not affect accuracy in any way , by the time the gas port is eroded enough to affect accuracy, the throat is gone and the barrel is toast anyway. I can see no point in paying extra for a gas port located in a groove. If your barrel is quality and your smith knows his stuff the gun will be accurate regardless.
 

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Way back when... whenever that was, Military armorers who built match grade M14 rifles always specified that the gas port should be in the groove. It had more to do with accuracy than anything else. It's a bit of a trick to get the port centered in the groove, but Krieger seems to have it aced. Criterion is a little hit and miss, but still seems to maintain good accuracy.

It's much more difficult to hit the groove in a 5.56mm barrel. But then, it doesn't seem to make as much difference as it does in a 7.62mm barrel.
 
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