Octagonal Rifling

[Shippj]

Im curious having heard that Black Hole Weaponry (Columbia River Arms) is making bolt gun barrels. Does anyone have any experience with this type or rifling, or their barrels in a bolt gun chambered for a competition cartridge?

Some background: Octagonal rifling has been around for a long time, it is popular in pistols, Glocks are known for it also in AR's. Black Hole Weaponry is synonymous with an excellent quality AR barrel that will last. There are many "facts" or "myths" I have heard about these barrels and have never seen a quantifiable data to support them one way or the other.

Here are some of the fact/myths:

Polygonal barrels are hammer forged around a rifling "die" this induces greater stresses into the barrel that make it more prone to weakness. OR, this process, hammer forging, allows the grain structure to line up making it a stronger barrel.

Polygonal barrels are faster (I've heard claims of 50 FPS) because of a tighter seal around the bullet itself.

Polygonal barrels wear less due to less surface area of the bullet contacting the rifling.

Polygonal barrel cannot shoot lead bullets due to being more susceptible to leading.

Polygonal barrels need cleaned less, less copper is laid down buy the bullet.

So where is the truth, its hard to find definitive facts.

Does anyone here have any real first hand experience or data to support or refute any of these claims?

 

[brianf]

People may chime in and have some other experiences but as generic information, non customized barrels (im a results person by nature) these are facts...

using lead bullets will cause issues, there is a ton of build up. there are a few articles (glock from the early1990's police training) about having issues with lead.

no matter how many or what type of lands and grooves a barrel the amount of bearing surface is the same. a 4 groove barrel has the same amount of barrel touching as a 3 groove, a 3 groove just has thicker/wider lands. some people believe that a 5R (odd number of grooves) distorts a bullet less, the record books dont agree.

speed is a barrel by barrel variable. you can buy the same spec barrel from the same supplier/smith and the velocity will be different.

hammer forged and single point cut barrels have both set world records at camp perry and in bench rest competitions.

 

[WeiserBucks]

I had a Pac Nor poly rifled barrel years ago. It was as good as anything I've ever used and better than many .

 

[ohiofarmer]

. . .no matter how many or what type of lands and grooves a barrel the amount of bearing surface is the same. a 4 groove barrel has the same amount of barrel touching as a 3 groove, a 3 groove just has thicker/wider lands. . . .

Care to expand on this? Maybe I’ am being dense but I’’ have never once heard this. Nor, does it ring true to me. (Does not mean it is not...) Is there some standard, or percentage of bearing surface in relation to bore diameter, out there and I’ have been living under a rock? Thank you

 

[brianf]

I'll try to find the article that was in precision shooting about the ratio of lands to groove.
the article was about 338 lapua barrels, how people thought a 3 groove would have less threat erosion than a 4 groove because there was more material touching the bullet. But really it was the same amount of barrel touching it was just wider etc. then they had some numbers.
You can also click around on the hide, frank green (bartlien barrels) or mike r (tac ops) were spreading their knowledge one day. I should have tagged it, those guys speak I generally listen. Lol

 

[Shippj]

Curious because it “seems” that more rifling would have more surface area in contact with the bullet. Octagonal barrels are used a lot over in Europe I believe. I was considering getting one, but with money being a finite resource I am more apt to stay with tried and true. I know Glock had some leading issues, not sure it was because of the barrel or their chamber though.

 

[brianf]

If they were the same dollar I'd say get one because you will have your own info, but if you looking for a match barrel go to a big name in a common twist and don't look back.
tac ops uses 4 groove cut barrels and gives their 1/4" guarantee (don't want to start a war..) but if they thought a 5r would give them less than that or make it easier to produce they would do it.

 

[308pirate]

Barrels die by throat erosion due to flame cutting. They don't die because the rifling ahead of the throat wears out. It amazes me people still argue this BS. Surface area considerations are irrelevant when it comes to barrel fouling when other factors (such as bore surface roughness) are orders of magnitude more important.

Polygonal rifling is NOT incompatible with lead bullets. Its is incompatible with lead bullets only for shooters who do not know how to select bullets of the correct hardness range for the application. There are even relatively easy formulas online to decide what hardness to use based on the application and some bullet casters publish their alloy hardness for each bullet. If you know nothing about cast lead bullets stay away from them, if you know what you're doing they pose zero risk in polygonal handgun barrels. I shot crapton of cast lead bullets with a Brinell hardness of 12 in near +P reloads through a Glock 17 with minimal fouling that occurred only near the muzzle after several hundred rounds. And I did so time and again. IDGAF what Glock has to say about it because they're just playing corporate CYA. Another BS myth created by ignorance.

Hammer forging will definitely impart tremendous stresses into the barrel steel and those stresses have to be relieved without distorting the barrel or else it will shoot like shit. It takes a significant amount of metallurgical knowledge and practical skill to do this. Whether cold forging aligns the grain structure like hot forging does, I do not know. It's plausible but I'm not sure about it.

 

[Mr.BR]

Im curious having heard that Black Hole Weaponry (Columbia River Arms) is making bolt gun barrels. Does anyone have any experience with this type or rifling, or their barrels in a bolt gun chambered for a competition cartridge?

Some background: Octagonal rifling has been around for a long time, it is popular in pistols, Glocks are known for it also in AR's. Black Hole Weaponry is synonymous with an excellent quality AR barrel that will last. There are many "facts" or "myths" I have heard about these barrels and have never seen a quantifiable data to support them one way or the other.

Here are some of the fact/myths:

Polygonal barrels are hammer forged around a rifling "die" this induces greater stresses into the barrel that make it more prone to weakness. OR, this process, hammer forging, allows the grain structure to line up making it a stronger barrel.

Polygonal barrels are faster (I've heard claims of 50 FPS) because of a tighter seal around the bullet itself.

Polygonal barrels wear less due to less surface area of the bullet contacting the rifling.

Polygonal barrel cannot shoot lead bullets due to being more susceptible to leading.

Polygonal barrels need cleaned less, less copper is laid down buy the bullet.

So where is the truth, its hard to find definitive facts.

Does anyone here have any real first hand experience or data to support or refute any of these claims?

Polygonal barrels are not exclusive to hammer forging
Bullet seal - Polygonal rifling patern is typicaly specific to bullet type , lead bullets vs jacketed bullets, most poligonal rifling you see in rifles is not poligonal bore of Metford type but its more of a trade lingo now for very rounded rifling patern , bullet when shot still has rifling patern vs being deformed to octagonal shape.

Bullet is only faster if has more friction hence higher pressures , which would sugest deforming bullet takes more 'umph' than cuting rifling groves.

Poligonal is used with lead bullets more than with jacketed
And how is it leading more but copper fouling less?

True poligonal rifle barrel is what Sabatti call multiradial rifling , its a metford type bore of sightly octagonal shape.
They use much of the same lingo .

'', the bullets are pressure formed following a circumference and not cut like in traditional rifling (pic. 1) which extends the life cycle of the barrel. Also there is no sharp corner to fill like in the other rifling systems (pic. 1 & 2), therefore the barrel is cleaner and wears more slowly.''

So far my i see my barrels burn out and firecrack i have yet to 'wear' one out , most of the claims are kinda BS.
Other thing is hammer forging can make great barrels (look at tikka) but ts not something in realm of small barrel maker like cutrifling

http://www.italianfirearmsgroup.com/...radial-rifling

 

[SubOptimal]

In normal rifle barrels it offers no particular advantage or disadvantage. The bullet will be slightly swaged to conform to rifling grooves or the bearing surface. I don't do any lead casting any more, that is pretty much a dark art and too much depends on the quality and composition of the casting materials and the size of the swaging die relative to the true bore diameter. My H&K USP pistol has polygonal rifling, a hex if I remember right. It is accurate, for a pistol, and I see no signs of copper fouling. As to bearing surface, inscribe a bullet diameter circle inside a hex, octagonal or even dodecagonal polygon and you will find the difference in contact area to be minimal. Rifles, with their higher velocities, need a smoother bore to prevent wearing out the barrel in the rifling area and to promote the higher velocities. Straight is pretty important as well. You will still more likely wear out the barrel throat long before the rifling wears. I don't know enough about metallurgy to know about cold forging vs cut rifling in terms of induced stress, I never studied it and am now too old to worry about it.
My hand lapped Rock Creek bbl that I got from Accurate Arms shows no copper fouling whatsoever, accuracy really doesn't start dropping off from its nominal <0.4" groups till 400 rounds or so. A better shooter than I might notice something, I don't.

 

[Shippj]

As I stated above I am not going to buy one, (I had considered getting a BHW bolt barrel though) due to too many variables. A cut rifle barrel is a known quantity with proven results.

I also understand that barrels wear mainly by throat erosion, but this question was a matter of statements I had heard in passing and on the internet about polygonal barrels in rifles.

It seems counter intuitive that more friction would have more velocity. A tighter seal would absolutely have better capability to retain gasses and allow more velocity. But if gasses are escaping past your bullet you are going to see scoring at some point down your barrel.

We we have to conflicting views above that wear is lessened on the polygonal barrel.

I searched a lot on the hide looking for this info, I’m a long time lurker.

So the question is purely hypothetical all things being equal will a polygonal barrel perform better than a cut rifle barrel?
Has there ever been a test either way? I’m sure there has but my google-fu is weak and I cannot find it.

 

[Shippj]

Here is the podcast that got me looking into this whole polygonal vs cut rifle barrel thing. http://hwcdn.libsyn.com/p/6/b/b/6bbc...5cce8da41ea064