GUNS Magazine What Is 5R Rifling?

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5R rifling has been around 40-plus years now but judging from the questions I’ve heard there seems to be little information on it. I am going to attempt to answer some of these questions. But first I would like to give you some history on the origin of the 5R rifling pattern.

Part art, part science — John Krieger barrels a rifle in his shop.

In The Beginning

Back in the early 1970s I began competitive shooting in NRA matches. Through this I met Boots Obermeyer, a barrel maker in southern Wisconsin. Boots made barrels by the single-point cut-rifled method. Being a machinist myself, and fitting my own barrels, led to Boots and I having many interesting conversations — we talked about barrel making, chambering, tools, etc.
Around the mid-’70s Boots came out with the 5R rifling pattern. How this came about was related to me directly by Boots and, to the best of my memory, is as follows.

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The Story

A reporter from Soldier of Fortune magazine had acquired a quantity of Russian ammunition. It was believed at the time Russian ball-powder technology was way ahead of ours. This acquisition presented an excellent opportunity to find out if this was in fact true. The ammunition was sent to Aberdeen Proving Grounds for testing.

The Russian barrels intended for us with the ammunition had what might be called 4-R rifling. The barrels were hammer-forged and had a peculiar slope-sided rifling. The slope-sided rifling was to make the hammer forging process easier by not having to get the steel to flow into the sharp corners at the bottom of the groove. Boots was contacted to make test barrels as his single-point cut rifling lent itself to making odd things such as this rifling form. He also enjoyed doing projects like this and had done things before for Aberdeen.

To properly test ammunition requires test barrels which, as closely as possible, represent the barrels of the rifles using the ammunition in the field. After Boots made the needed test barrels, the end result was not only were the Russians not ahead in their powder technology, they weren’t even up to where we were at the time.

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A Sunnen hone is another piece of equipment in the Krieger shop used to improve bore finish.

Curiosity Sparks Invention

During this process, out of curiosity Boots made a barrel for himself in 5-groove rifling and was very impressed with its accuracy. It ultimately became his contribution to target shooting. For the record, Boots never claimed to have invented the 5R rifling pattern, only developing it for target shooting. The “R” refers to the Russian background.

I once came across an 1861 English patent for a rifling head showing a 5R pattern of rifling as an example.

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The 4-groove rifling profile: If you focus on the grooves, you’ll see the sides are parallel,
while if you focus on the lands, the sides appear angled.

The 5R profile: Using an odd number of grooves, plus highly angled land sides,
is reputed to give better accuracy — at least some people believe.

Six-groove rifling again has groove sides parallel but the land sides are less angled than in 4-groove.

Definitions

5R is a 5-groove rifling pattern with sloped or angled sides to the lands. All rifling has a certain amount of angle to the sides of the lands as a natural effect of the rifling process. The sides of the grooves are parallel, but the sides of the lands are not and the 5R carries this to an extreme.

So why should this be good? It is felt the 5R may seal off the bullet better. Also, the angle of the lands may be less stressful to the bullet jacket, so thin-jacketed match bullets would be less likely to come apart at the high spin rates longer bullets require. It is also felt to be easier to clean as there are no tight corners next to the lands to hold powder fouling.

The 5-groove type of rifling comes from the belief an odd number of grooves is also less stressful to the bullet because it doesn’t have two lands directly across from one another. The British have historically favored odd grooves for their rifles. Double rifles for example often have seven grooves with each barrel having a land at 6 o’clock. American manufacturers occasionally employ odd grooves as well. I have seen 5-groove barrels on some .22 rimfire rifles.

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Angles

What is the proper angle on the side of the 5R lands? This is proprietary and it has evolved over the years.

Some time ago Boots had a customer with a government contract for their rifles using the 5R barrels. Boots supplied the barrels for years. Then, the order was increased and being a one-man shop Boots couldn’t meet the increase. He suggested they contact us at Krieger Barrels to handle the increased quantity.

We accepted the contract but I wanted to know what the 5R profile was so we would do it properly, the way Boots wanted it. I went down to Boots’ shop so he could show me the proper angles and dimensions. Are the exact angles, etc. important? I don’t know, but Boots thought they were and if it isn’t his angles, then it’s not really 5R!

Rifling 101

There are a number of different rifling forms, numbers of lands and grooves and combinations thereof brought out over the 500 or so years barrels have been rifled. There are even some early German barrels with straight grooves. Each one carried with it reasons why it was supposedly better.

Rifling is actually much shallower than it appears. For example, on a .30 caliber barrel the grooves are 0.308″ or bullet diameter, 0.008″ overall with 0.004″ to each side. This is the height of the lands and is only slightly taller than the thickness of a sheet of writing paper. One may wonder how much effect it could possibly have on the bullet but consider it takes a bullet at rest and in a millisecond or so winds it up to maybe 200,000 RPMs!

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A highly-modified — by Krieger — Pratt and Whitney 1/2 B-50 rifler is another special
piece of proprietary equipment at the shop.

As far as which type of rifling or number of lands and grooves shooting better than another, I know of only two instances where it was felt a certain number of lands was better than another. One was “leg matches” where shooters were required to shoot the military ammo issued at the match. It was felt by significant numbers the .30 173-gr. bullet shot better in a 4-groove barrel than in a 6-groove barrel. This was more subjective than scientific. In another instance, a more scientific test was performed with one specific bullet. I seem to recall it might have been the “famous” Herter wasp waist. It again was found to shoot slightly better in a 4-groove barrel than it did in a 6-groove barrel.

In both of the above two examples, the bullets seemed to favor the 4-groove barrel. Was it because the 4-groove barrel has more slope to the sides of the lands (see illustrations on p. 47) than the 6-groove barrel? If so, then maybe the 5R offers an advantage having more slope yet. I can see no disadvantage in 5R rifling compared to conventional rifling and it may actually help with some of the odd problems occasionally occurring.

Ultimately …

When I was shooting competitively, I shot both 4-groove and 5R barrels and never felt any advantage of one over the other. However, these matches from 300 to 1,000 yards were shot prone with a sling. The most accurate rifle on the line didn’t always win the relay or the match. We didn’t have VLD bullets then, with their high spin rates. The barrels all had their likes and dislikes, and none of them could make up for a poorly executed shot. They all went right where they were directed to go.

John Krieger is the founder of Krieger Barrels Inc., makers of precision single-point cut-rifled barrels since 1982.

www.kriegerbarrels.com

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