Why do grooves have square corners for fouling?

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John Alexander posted this 28 July 2019

It would be a lot easier to get all the fouling out, especially lead slivers, if rifling grooves didn't have square corners at the bottom.

I understand why they are easier to make square for both cut rifling and button rifling but with manufacturers going to hammer forged it would seem at least as easy to make the mandrel with rounded or beveled edges and should not affect the effectiveness of the rifling.

Is this just what is expected to sell rifles or is there a good reason?

John

 

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Ross Smith posted this 28 July 2019

You can get round bottom groove black powder barrels.

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RicinYakima posted this 28 July 2019

I have both a Newton .30 Model 1906 and a Pope barrel with different bottom configurations. The answer is: What is the cheapest way can we make cutters? Now it is traditional, but no good reason. FWIW

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JeffinNZ posted this 28 July 2019

My Colerain MLer round ball barrels are round bottom rifling.  Sweet for cleaning and loading.

Cheers from New Zealand

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Chickenthief posted this 28 July 2019

The first Danish Krag-Jørgensen rifles had an almost hexagonal rifling. It was designed for black powder and jacketed bullets.

It's downfall was that it got worn out way to fast.

Top half is the 8x58RD with compressed black powder charge (72grains with a 8 grain booster charge of lose bp).

Bottom is the modified Metford rifling.

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Lee Wiggins posted this 28 July 2019

   In the original question , I am wandering if the lube grooves in the bullet is what is being asked. Actual square grooves would make it a bear to get the mold to drop bullets but a little angle on the groove fixes that. I think grooves forward of the rear groove which is lubed act as scrapers to try to maintain bore condition. This is just an idea and I don't know if it has merit. Also I might be misreading the question.

   Lee Wiggins 

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Brodie posted this 28 July 2019

The Whitworth rifle and cannon (and the Pedesoleri repoductions of same were all made to shoot black powder and, have/had hexagonal rifling to reduce fouling from black powder.  I could shoot my rifle all afternoon and never have to clean the bore while on the range.

B.E.Brickey

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Brodie posted this 28 July 2019

All the original "Keith" designs had square cornered lube grooves.  I think that it is a hold over from the black powder days.  The grooves were designed like that to hold more lube to prevent fouling and keep the BP fouling soft.There was also the belief that square corned grooves helped to scrape the fouling from the barrel with each shot.

B.E.Brickey

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45 2.1 posted this 28 July 2019

^^^^^^^^^^^ Those grooves aren't quite square, they have a slight draft to them...... at least the "Ideal" molds I have that do have those square lube grooves in them that I've measured and duplicated in some molds.

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RicinYakima posted this 28 July 2019

Truer would be "flat bottom" grooves.

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Ken Campbell Iowa posted this 29 July 2019

... just a comment that sharp cornered cutting or swaging tools wear/break faster, so there must be reasons other than manfacturing cost that results in square grooves in both barrels and molds.

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Hornet posted this 29 July 2019

   Assuming that we're still talking about the actual rifling grooves that John started with, back about 60 years or more ago a barrel maker named Boots Obermeyer made some fame with his 5-R rifling that had very small radii on the inner and outer corners of each rifling land. The claim was that it made fouling much prone to accumulate and easier to remove and many of the shooters using them substantiated this claim. I'm fairly sure that he did not actually create the concept (there's been LOTS of different rifling types) but he did popularize it at the time. I recall seeing a recent ad from a current manufacturer claiming to use 5-R rifling so it may be making a comeback.

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TRKakaCatWhisperer posted this 30 July 2019

Interesting (5R).  When I worked for a machine-gun manufacturer, I talked with a number of barrel manufacturers.  There is a wide variety of forms of rifling.  Sometimes the inside radius would be created by worn cutters - FWIW.

 

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John Alexander posted this 30 July 2019

Seems like a radius caused by a worn cutter, or anything else, would help the shooter trying to get fouling out of the bore.  Maybe the almost universal practice of making hard to clean rifling, even it might be easier not to, is "just the way we do it" which is the explanation for a lot of stupid practices.  

It's OK, us old guys are allowed to be grouchy about minor irritations.

John

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.22-10-45 posted this 22 January 2022

The early .303 British rifles of the late 1880's firing a compressed charge of black powder were rifled with Metford type shallow rounded groove rifling.  They switched to the deeper Enfield square type because of jacketed bullet/Cordite erosion wear.  My 1895 Winchester-Lee 6mm sporting rifle is rifled

with the Metford rifling.  This rifling type was reported to be more accurate with lead bullets..as attested by the number of British match rifles of the later 1800's using it.

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MP1886 posted this 22 January 2022

   Assuming that we're still talking about the actual rifling grooves that John started with, back about 60 years or more ago a barrel maker named Boots Obermeyer made some fame with his 5-R rifling that had very small radii on the inner and outer corners of each rifling land. The claim was that it made fouling much prone to accumulate and easier to remove and many of the shooters using them substantiated this claim. I'm fairly sure that he did not actually create the concept (there's been LOTS of different rifling types) but he did popularize it at the time. I recall seeing a recent ad from a current manufacturer claiming to use 5-R rifling so it may be making a comeback.

 

I understand the original 5-R rifling to be a true "rachet" type rifling far diferen't then what they are calling 5-R today. Many of the 5-R riflings of today have slight slanted sides ond both sides of the groove. That is not true "rachet" rifling. Just my take on it. 

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Bud Hyett posted this 22 January 2022

The grinding wheel shaping the cutter is easiest set to straight sides and flat bottoms. Any variation to this grind for a different rifling form greatly adds to the cost. And building tooling to repeat the from also adds to the cost. Plus there must be an "Economic Order Quantity" to justify the overall expenditure where the burdened cost to the tooling is spread over many barrels. 

At one time, labor was cheap and people could spend the time forming the grinding wheels to produce these cutters. Today, not so. The person setting up the grinder to sharpen the cutter must understand the  process and sharpen in a minimum of time. The cutter and button made today lasts longer in usage than a half-century ago, but it will need sharpening.

One other consideration is todays' barrels produce great accuracy. The one adjustment needed is the nut behind the buttplate. Why go to the added cost of a new (reborn old) rifling form when it will not shoot better than the current offering?

All businesses are run by the accountants in the final summation. If the product costs too much to sell and has a limited market, they will not build it. Note: I've always wanted to try the Shilen 5R rifling on cast bullets in a superior action and stock that I know shoots, but Shilen no longer offers it.

In my two Stevens 44 1/2 actions, I have two Shilen, one Krieger, one RKS gain twist barrel. All shoot far better than I can right now, but I'll keep practicing.

Final thought - In today's technological world, if everyone does not want it, no one gets it.     

Rifling Types - Layne Simpson

Farm boy from Illinois, living in the magical Pacific Northwest

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mashburn posted this 22 January 2022

Here Is A Different Opinion

We all know that the sides of the grooves are perpendicular. When a bullet is forced through the barrel the perpendicular flat side is embedded into the bullet and causes it to rotate. If the bottom corner of the groove was radiused, that would make the flat sides of the grooves shallower, which would make less contact with the bullet. If the corners were radiused the grooves would have to be made deeper to compensate for the corner radius and therefore the bore would have to be made smaller.

I know nothing of all of the old types of rifling I've owned a few but that doesn't give me any knowledgeable information. I think Ken made a good point when he stated that the barrel makers probably had a good idea for making the corners square.

About 14 or so years ago when I was building extremely accurate varmint and hunting rifles for myself and John Q Public, here is what I learned about barrels and barrel blanks. I put them into 3 categories: FOULERS, SEMI-FOULERS AND NON FOULERS. FOULERS ARE CHEAP, SEMI-FOULERS ARE MUCH MORE EXPENSIVE AND NON-FOULERS ARE MUCH, MUCH MORE EXPENSIVE. Some  .Semi foulers after some hand lapping and about 1.000 rounds of jacketed bullets often will turn into non foulers.

I know a bunch of you are going to jump all over my theory, but I thought this was a place for discussions of possibilities.

Mashburn

David Cogburn

David a. Cogburn

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RicinYakima posted this 22 January 2022

For cast bullets, the square corners allow gas leakage and leading. Land height is determined by bullet alloy, as soft bullets only need three or four thousandths lands. 

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mashburn posted this 22 January 2022

Ricin,

There are a lot more people who don't shoot cast bullets than those who do such. I think that land height for cast bullets, if they had a radius in the corner, would have to be higher. I'm surprised to hear some of you people admit that you have lead fouling. Nearly all the reports that I have read, say that if you are getting lead fouling, you don't know what you are doing.

Mashburn

David a. Cogburn

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Spindrift posted this 22 January 2022

The Italian Sabatti use a concept they call multiradial rifling, that looks a little like a Pope- barrel. 

 

The producer argue that this form of «rifling» give less deposits, longer barrel life and very good accuracy. But it is not uncommon for producers to make high claims for their product, of course.

 

They also claim the forcing cone in these barrels provide a more gentle and effective self- centering transition for the bullet

 

 

I’m not saying we should believe everything a company claims about their product. But I must admit, I’m curious how such a rifle would perform with cast bullets. I think this concept could work very well. Maybe I have to get one of these.....

 

https://www.sabatti.it/en/mrr-rifling

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John Alexander posted this 22 January 2022

I believe Bud's answer is spot as the answer to my question. Just as I assumed in my starting post. Manufacturing cost is the reason along with the fact that square bottom grooves work and jacketed bullet shooters worry less than CB shooters about fouling and they are the main market. Pity. I guess we are going to have the PITA of sharp corners that are hard to clean.  The good news is probably they don't have to be absolutely clean for top accuracy.

I have enjoyed all the viewpoints bought to this thread.

John

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MP1886 posted this 22 January 2022

For cast bullets, the square corners allow gas leakage and leading. Land height is determined by bullet alloy, as soft bullets only need three or four thousandths lands. 

 

Ric I don't see it the way you do.  I see shallow grooves for hard bullets such as jacketed.  Thus why we see shallow grooves in modern rifles today. Deeper grooves were/are seen on BP firearms, but they too have been leaning towards the more shallow side. Once I was talking to a well know barrel maker and we were discussing button rifling.  I must have said something about button rifling not being deep. He said you can button rifle quite deep, then he said "You must be a cast shooter".   I laughed and said that I am. 

On another note for no corners how about hexagonal and polygonal rifling?  

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RicinYakima posted this 22 January 2022

MP,  And that is why BP guns shoot so much better with soft alloys rather than linotype.

I have an original Newton rifle in 30/06 with this bore form, as seen below, that shoots very well with any alloy I have tried. These are linotype Lyman 311284 and Lyman 311440

And the targets look good for a post front sight and Lyman 48 rear.

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MP1886 posted this 22 January 2022

Ricin that Newton kind of looks like polygonal rifling. I have a Glock 45acp with Glock's hexagonal rifling and it will outshoot  most people's tuned 1911's using cast. I have a HK UMP with HK's polygonal rifling  and it definitely will outshoot anyone's tuned 1911. Neither of the two lead. That's myth about Glocks and not using cast in them and I know the reason why Glock said not to shoot cast.  The problem has been eliminated, but Glock won't change their policy. 

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Eutectic posted this 01 February 2022

Glock and H&K have been making polygonal rifling for years. I think H&K may also use it in their rifles. It has been concussively proven by myself and others you CAN lead a polygonal bore.  Is cleaning easier? Yes maybe. Is smooth rifling a cure-all for cast bullet ills. Not in my experience, you still have to be careful with alloy hardness, bullet diameter and load. 

If <5% of people want it they better forget about it if it costs anything extra to make it.

Steve

 

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