Rifling revolutionized!

by Tom Gaylord
Writing as B.B. Pelletier

This report covers:

  • Outside the box
  • Rosenthal award
  • Rifling
  • How it works
  • Outside rifling?
  • Accuracy
  • Range increased by orders of magnitude!
  • Trouble brews
  • What is to come?
  • Rumors are flying!
  • Summary

Outside the box

I’m sure you have heard the phrase, “Think outside the box.” Many organizations don’t really want their people to do that. The organization just wants their employees to enlarge the box a little, but to continue to respect the time-honored principals that got the organization to where it is today.

Rosenthal award

But there are exceptions. In engineering there is an annual Sol Rosenthal Award for the creative idea that best advances its technology that year. Unlike many awards, there is only one caveat to this one. A prototype of the idea must be implemented, so it can be compared to an existing reality that can be measured. read more


The invention of rifling: Part 1

by Tom Gaylord
Writing as B.B. Pelletier

The history of airguns

This report covers:

  • Nobody knows when rifling was invented
  • What is rifling?
  • The first rifling
  • Gunpowder leaves dirt in the bore
  • Minie Ball
  • Trapdoor Springfield development
  • Ballard rifling
  • Airgun rifling

Nobody knows when rifling was invented

I’ve been reading about guns for 56 years and the one subject that has always baffled the experts is rifling. When was it invented? By whom? What gave them the idea? One thing is certain — the Wiki piece on rifling is entirely fabricated. It says “Rifling was invented in Augsberg, Germany, at the end of the 15th century. It would be wonderful if that were true, but the fact is nobody knows where, when or why rifling came into being. To be fair to Wiki, I have read other accounts that claim people in the 1400s were thinking of spinning a ball for stability in flight because they knew the fletches on arrows stabilized them the same way. The truth is, though, no one knows for certain when rifling came into being. It is entirely possible it came from several locations around the same time.

What is rifling?

Rifling is a set of parallel raised ridges called lands and grooves that run down the inner bore of a barrel. Today these lands and grooves run in a spiral path relative to the bore’s axis, but that wasn’t always the case. The purpose of the grooves and the lands that stand up between them is to spin the bullet to impart gyroscopic stabilization as it flies through the air. I will talk more about the specifics of that stabilization as this report progresses.

Rifling

Cross section of a rifled bore.

The first rifling

Back in the 1960s I read somewhere that the first rifling was straight. The lands and grooves ran parallel to the axis of the bore. This was an attempt to keep the bore of a gun clear of deposits, so the gun could be shot longer before cleaning was required.

Gunpowder leaves dirt in the bore

The gunpowder of that era is what we call black powder today. It generates a residue of no less than 55 percent of the solid mass of its initial volume. Some of this is seen in the dense smoke that comes out of the muzzle. The rest of the residue is in the form of deposits that remain in the bore of the gun. A black powder gun can get so dirty that you cannot ram a ball down the bore in as few as 5 shots.

Early shooters compensated by loading smaller balls as the bore clogged up, but that solution wasn’t good. Cleaning black powder deposits from the bore of a gun takes many minutes and requires the use of water. Water left inside the barrel will ruin the next powder charge that gets loaded. So the barrel had to be thoroughly dried between cleanings. A better solution needed to be found.

Straight scratches that run down the inside of the bore were tried, in the hopes that the deposits would collect in them and leave the main bore free for more shots. It must have worked to some extent, because many gun makers started doing it. Then someone had the brilliant idea to cut the scratches in a spiral. That made them longer than the length of the bore, providing more space to hold gunpowder residue. And when they did that it wasn’t long before they noticed a marked improvement in the accuracy of the barrels rifled this way. What I am describing now took many years to unfold. It wasn’t an overnight phenomenon. But it did catch on, and then it began to evolve. Rifling took on many shapes over the next few centuries, as inventors tried every possible thing. The width of the lands and grooves was varied to see what worked best.

rifled bore

This early Kentucky rifle (1730-1750) had wide lands and narrow grooves that were deep. It didn’t work too well.

rifled bore

Here’s some aggressive rifling!

As the centuries passed, barrel makers learned that the lands were what spun the ball (all the bullets were still lead balls at this time). Someone (in Prussia ?) discovered that a ball that was inside a tight-fitting thin leather patch would be easier to load, because the ball could be smaller than the bore and the patch would make up the difference.

That idea came to the American colonies within a few short years, where it rapidly evolved into the famous Kentucky rifle that shot a patched bullet — a round ball enclosed in a tight-fitting cloth patch that filled the rifling and spun the ball. The patch cleaned the deposits from the bore both at loading, when it was rammed down the barrel, and again when it was shot.

The Kentucky rifle was a huge advance in firearms because it allowed the use of smaller bullets (balls), because of the tight-fitting patch. A longer barrel allowed the rifle to extract all of the energy that was in the gun powder, so the rifle shot harder than ever. And it was also more accurate. Accuracy, speed, power and economy of powder and lead. These are all the things that the Kentucky rifle brought to the table. And rifling continued to advance.

Minie Ball

If it seems odd to call a round ball a bullet, it must also seem odd to call a conical bullet a ball, but that is exactly what the Minie Ball is. Claude Minie and Henri Delvigne came up with a bullet in 1849 that had an iron cup in its base. The bullet was smaller than the rifle’s bore, so it loaded easily, but when the gun fired, the iron cup was driven into the base of the bullet, expanding it to fit the rifling tightly.

Later it was discovered that the bullet would expand if the base was simply left hollow. That simplified its construction. The Minie Ball is one of the earliest successful conical bullets and the hollow base variation of it was widely used during the American Civil War, where it took rifling to the next level. Military leaders learned that conical bullets were far more accurate than plain round balls at long distances. The Civil War has several instances of sniper kills at greater than a half mile distance. These were not with Minie Balls however.

Minie Ball

These are not true Minie balls. They are a second-generation bullet that has a hollow base to expand into the rifling. They are fast-loading and keep the bore cleaner than patched balls.

In truth conical bullets were already in use among riflemen before the Minie Ball arrived on the scene, but the success of that projectile helped everyone realize the day of the conical bullet had arrived. After the Civil War the United States military embarked on a program to develop an accurate breechloading rifle that used the new self-contained cartridges. I may have to write a separate report about the development of the U.S. Rifle Model 1873, which is better known as the Trapdoor Springfield. Its development lasted over 8 years and went through several iterations of designs before settling on the final rifle and cartridge. It is the work on the cartridge, however that interests us today.

Trapdoor Springfield development read more


How does rifling twist rate affect velocity and/or accuracy? Part 13

by Tom Gaylord, a.k.a. B.B. Pelletier

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Part 8
Part 9
Part 10
Part 11
Part 12

This is the summary report in this series. I’ll give you my thoughts on how this test went, and I expect you to comment, as well.

The barrels
Three barrels were used in this test. One was the factory barrel that comes with the .22-caliber AirForce Talon SS. It’s a 12-inch Lothar Walther barrel that has a choke of about a half-thousandth inch reduction in the bore diameter for the final 2 inches of length. That makes all the pellets of uniform size as they leave the muzzle, and it may potentially stop any in-bore wobble. This barrel has the standard airgun twist rate of 1-turn-in-16-inches of bore travel, written as 1:16″.

The other 2 barrels were made by Dennis Quackenbush. Neither barrel is choked. One is a 1:12″ twist; the other is a 1:22″ twist. They’re also about 12-inches long and are held in the gun by AirForce Talon SS barrel bushings. Several comments have suggested that because these barrels are different than the Lothar Walther barrel, this test is somehow not fair. But the results of all the shooting prove otherwise. Sure, there are variations from barrel to barrel, depending on the power used and which pellet was shot. But the results are so close between all 3 barrels that whatever differences there might be are overridden by the similarities. In other words, I’m suggesting that if Lothar Walther had made all 3 barrels, there would be similar differences.

Talon SS precharged air rifle twist rate test 3 barrels
The 3 barrels used in the test. Factory barrel in the middle.

I believe the twist rates are what drive the results. We weren’t searching for the most accurate barrel in this test. We were looking for behavior changes as conditions were changed. And we got that.

Velocity
The first thing that was tested was velocity. Both pellets — the 14.3-grain Crosman Premiers and the 15.9-grain JSB Exact Jumbo were shot from all 3 barrels at each of 3 predetermined power settings. These settings were marked on the gun so they were kept constant throughout the test.

Talon SS power settings
The power settings were the power indicator screw all the way to the left (the lowest setting), and the power screw centered on each mark (settings 6 and 10).

 

07-24-13-01-Velocity-table

I reviewed the velocity for you in Part 8. Here’s a summary of that report.

In all cases, the velocity increased the most between power setting zero and setting 6. The velocity increase from setting 6 to setting 10 was always smaller than the increase from setting zero to setting 6, and that’s irrespective of the twist rate or which pellet was shot.

What you’re seeing here is the slowing down of the rate of velocity increase as the air flow increases. That’ll become clear in a moment when I discuss the rifle’s maximum velocity potential.

As the twist rate slowed (1:22″ is slower than 1:12″), the velocity increased at most power settings with most pellets. There was one instance with the 1:22″ barrel when the JSB Exact pellet actually went 2 f.p.s. slower at setting 10 than at setting 6; but with all other barrels and pellets, there was always a velocity increase as the power setting went higher.

Focusing on the 1:22″ barrel for a moment, we see that the velocity increases between setting 6 and setting 10 were not as great as they were in either the factory (1:16″) barrel or the 1:12″ barrel. This suggests what we have suspected all along — that the twist rate of the barrel does slow down the pellet as it gets tighter. And we can see from this test that the phenomenon is most apparent at the lower power settings. At the higher power settings, the differences seem to shrink, indicating that the influence of the power setting is overriding the influence of the twist rate. I believe this is an important finding, and it sets up the next observation, which is that the top velocity of the gun was fairly close for all 3 barrels, regardless of the twist rate. The type of pellet made more difference to the top velocity than the barrel twist rate did.

It should be obvious from these results that the Talon SS powerplant has upper limits that cannot be exceeded by forcing more compressed air through the barrel. This illustrates the relationship between barrel length and velocity in a pneumatic airgun.

A second thing I found interesting is that power setting 6 is very close in performance to power setting 10. In the case of the 1:22″ twist barrel, it’s remarkably close…but it’s close for all three barrels. A prudent airgunner might consider this when setting the power wheel adjustment on his Talon SS, knowing that a lower setting uses less air, yet gives velocity that isn’t that much slower.

A third thing is that the velocity performance of the 1:22″ barrel is so good at power setting 6 that it makes power setting 10 useless. Take that thought just a little farther, and you’ll see that all power settings above setting 10 are pretty much a waste of air in a Talon SS with a 12-inch barrel, regardless of which pellet you use.

Accuracy testing
Next, I tested all 3 barrels with both pellets shot at all 3 power levels at 10 meters (11 yards) and 25 yards. Following that, I tested all 3 barrels and both pellets, again, at 50 yards, only I didn’t use the zero power setting. This was where my eyes were opened regarding the effects of twist rate.

Accuracy table final

I analyzed the accuracy in 2 different reports. One (Part 9) was the 10-meter and 25-yard accuracy and the other (Part 12) was the 50-yard accuracy, alone. Now, with the table above we can combine these results and analyze all the accuracy data together.

The first observation I’ll make is that at 10 meters, I got 10-shot groups that ranged from as small as 0.092 inches to as large as 0.578 inches. The factory barrel gave the best results with the JSB pellet; but with the Premier, it was the 1:22-inch twist that did the best. Curiously, that pellet and twist rate didn’t seem to change that much as the power was increased (at 10 meters). With all other barrels and pellets, the group size did change a lot as the power changed.

It’s too simple to say the factory barrel with the 1:16-inch twist rate is the best; but of the 3 twist rates in this test, it certainly is the most flexible across the board. However, you’ll notice that the 1:12-inch twist barrel did shoot the best single group (with JSB Exact pellets) at 50 yards. That group is so close to the Crosman Premier group shot by the 1:16-inch barrel that I can’t call a clear winner — BUT — here is what I CAN say. The Quackenbush 1:12-inch twist barrel is certainly capable of shooting 50-yard groups at least as tight as those shot by the Lother Walther barrel; and in my mind, that puts the barrel-equivalency question to rest.

Another observation is that the 1:22-inch twist barrel was just as good at 10 meters as the other 2 barrels, in general, but look at how the groups opened at 50 yards! That says something very strong about the relationship of the twist rate to accuracy. And it also brings up a second observation.

Premier pellets and JSB pellets performed differently throughout this test. Just look at the 50-yard results for Premiers and JSBs with the 1:12-inch twist barrel, and you’ll see what I mean. This is one more bit of evidence that barrels have preferences for certain pellets.

Final observation
This will be my final remark in this series of reports, and it does not come from the data collected in this test but from the 5-part test of the Diana model 25 smoothbore. In that test, we saw that the smoothbore was able to place 10

JSB Exact RS read more


How does rifling twist rate affect velocity and/or accuracy: Part 12

by Tom Gaylord, a.k.a. B.B. Pelletier

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Part 8
Part 9
Part 10
Part 11

Today, I’ll report on the final test in this series. This isn’t the final report — just the final test, which is the barrel with the 1:12″ twist, shooting at 50 yards. Get ready to be surprised. I know I was!

I did this test on the same perfect day as the factory barrel that was reported last week in Part 10, and the weather was perfect most of the time. From time to time, there was a very slight breeze that I waited out before shooting. The shooting conditions were as good as they get.

AirForce Talon SS changing barrels Changing barrels took 5 minutes. The silver barrel has the 1:12″ twist.

I used the same two pellets we’ve been shooting all along, and they were shot at power settings 6 and 10…just like the other 2 barrels that went before. The gun was shot while resting on a sandbag that’s very stable. When the tank was filled or the power was changed, I always shot one shot to settle the valve. Experience tells me that’s all that’s needed.

AirForce Talon SS filling the tankThe tank was filled to 3,000 psi.

Power setting 10
I first shot both pellets on power setting 10. And 14.3-grain Crosman Premiers were hitting low and to the left. One of them only nicked the target paper, so I photographed the target before taking it off the backer paper, so you could see the complete group.

AirForce Talon SS Premier group still on target stand Here are the two 10-shot groups of Premiers. Notice that they’re hitting to the right of the aim point, which is the center of the bull they touch. The group shot on power setting 10 is at the top, and it shows why I like to use backer paper when shooting at 50 yards.

AirForce Talon SS Premier group 50 yards power 10 Premiers on power setting 10 gave this 2.577-inch group. See the nick on the right edge of the target paper? I had to guess a little for this measurement, but it isn’t too far off.

Then it was time to test the 15.9-grain JSB Exact Jumbo 15.9-grain pellet on power setting 10. This is where the surprise comes! Ten pellets made a 1.259-inch group! If you check back with the results the factory barrel gave, you’ll see that this group is very close to the best group made by the factory barrel (1.153″ for 10 shots with the same JSB pellet on power setting 6), and it’s equal to the group that was shot on power setting 10 (1.283″). This addresses a question many of have had from the beginning of this test — namely, are the Quackenbush barrels equal to the Lothar Walther barrel?

AirForce Talon JSB Jumbo group 50 yards power 10 JSB Jumbo 15.9-grain domes on power setting 10 gave this 1.259-inch group. This shows that the 1:12″ barrel can be accurate at 50 yards. read more



How does rifling twist rate affect velocity and/or accuracy? Part 10

by Tom Gaylord, a.k.a. B.B. Pelletier

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Part 8
Part 9

Today, we’ll begin looking at the effects of the rifling twist rate on the accuracy of our test AirForce Talon SS rifle in .22 caliber at 50 yards. If you’re prone to jumping to conclusions before all the data is in, I have to caution you that today’s test will look bad because I’m testing the custom barrel that has the 1:22″ rifling twist. We know from the earlier tests that this barrel was most accurate at 10 meters on power levels zero and 6. Above that power level and also out at 25 yards, the accuracy of this twist rate broke down. So, it would be reasonable to assume that this barrel will give results that are even worse at 50 yards.

That didn’t stop me from trying my hardest to shoot well. I was able to watch each pellet go into the target paper because of the distance, and that was disconcerting when the pellets landed so far from the aim point and from each other. Let’s take a look at how the rifle did.

The day was nearly perfect, as it has to be to get good accuracy from pellets at 50 yards. The air was calm, except for some light breezes from time to time. I was able to work around these breezes and get the results I was after.

I decided not to test the rifle on zero power because of the long distance to the target. Any breeze would have so much time to blow the pellets off course that I felt it wouldn’t prove anything. So, both pellets were shot on power levels 6 and 10. That’s how I’ll test all 3 barrels.

You may remember that this barrel produced velocities that were very close to each other at power levels 6 and 10. With 14.3-grain Crosman Premiers, the respective velocities were 840/854 f.p.s.; and with 15.9-grain JSB Exact Jumbos, the velocities were 817/815 f.p.s. We expect the pellets in this test to go to the same place on the target, and I would expect the two groups for each pellet to be pretty similar in size.

Crosman Premiers
I started with Crosman Premiers and the power set to 10. I did not adjust the scope since completing the 25-yard accuracy test and the center of the group landed about 3.9 inches below the aim point. Ten pellets went into a group that measures 2.04 inches between centers.

Talon SS rifle Premiers 50 yards power 10
Ten Crosman Premiers went into 2.04 inches at 50 yards on power setting 10. The center of this group was about 3.90 inches below the aim point with the scope set for 25 yards. The pellet at the top center is part of another group — not this one. I did account for the full size of the pellet on the left that just clipped the edge of the target paper.

On power setting 6, the center of the group also struck the target 3.90 inches below the aim point. These measurements of the groups are just approximate since the center of each group was difficult to locate precisely. The 10-shot group size on power setting 6 was 2.607 inches between centers. This is slightly larger than the group shot on power setting 10.

Talon SS rifle Premiers 50 yards power 6
Ten Crosman Premiers went into 2.607 inches at 50 yards on power setting 6. The pellet hole at the lower right is not part of this group.

JSB Exact Jumbo
Next, it was time to test the JSB Exact Jumbo pellet. I started with power setting 10. The center of the group landed about 4.25 inches below the aim point.

Ten pellets shot on power setting 10 went into a group that measures 2.509 inches between centers. The group is much taller than it is wide.

Talon SS rifle JSB Heavys 50 yards power 10
Ten JSB Exact Jumbo pellets went into 2.509 inches at 50 yards on power setting 10. The group is taller than it is wide for reasons unknown. read more


Rifling twist-rate primer: Part 1

by Tom Gaylord, a.k.a. B.B. Pelletier

Recently, we have had a number of questions about rifling twist rates that were attached to the twist-rate report. These questions are extremely important to the understanding of how bullets and pellets are stabilized, so I’m starting a tutorial on rifling twists today. I’ll keep adding sections as I see the need to explain more about the topic.

Today, I want to lay a basic foundation of what the rifling twist rate does. Blog reader Feinwerk asked if centerfire rifles (he said higher-power firearm rifles) had different twist rates than rimfire rifles, and the answer is yes. I’ll get to that, but let me start at a time when things were much simpler.

Early firearms shot multiple projectiles, similar to today’s shotguns that shoot birdshot and buckshot, but much cruder. It wasn’t long before people started experimenting with single projectiles. They found that single projectiles retained more of their initial energy than many smaller projectiles, so they did more damage when they connected with a target. The problem was getting them to connect.

After much experimentation, people discovered that spherical projectiles were the best for firearms. They flew the straightest because they didn’t have the irregular surfaces that created low-pressure zones to guide the bullet astray.

Then, rifling was discovered. Straight rifling (straight lands running parallel to the axis of the bore) was first used as a means of holding all the unburned gunpowder residue, of which there was much. That allowed the gun to be fired more times before cleaning. And, at some point, someone cut the grooves in a spiral — to make them longer to hold even more residue? We’ll never know for sure.

Once people saw how much straighter a spinning ball flew compared to one that was not spun intentionally, the race was on. For hundreds of years, the spinning round ball was the only bullet that was known. It reached its zenith as the patched ball used in the American rifle we know as the Kentucky — where the rifling doesn’t even engrave the lead ball, but spins it by spinning a cloth or leather patch that holds the ball tight while it’s inside the barrel. The ball gets very little distortion from the barrel — although there is a pattern around its circumference where the rifling pressed against the patched ball.

When the patched ball exits the muzzle, the patch falls away and only the bullet travels on to the target. Accuracy increased with this system, and the loading time dropped because the shooter didn’t have to engrave the lead bullet with the rifling when he loaded the bullet/ball.

The conical bullet
Things never stand still, though, and after the patched ball came into general use shooters began experimenting with bullets that were not balls, but rather longer cylinders of lead. These were the first conical bullets.

ball and conical bullet
Although the round ball is very close to the same diameter as the conical bullet, it takes a lot more spin to stabilize the longer, heavier conical bullet.

A ball doesn’t need to spin very fast to be stable because its surface is smooth and regular. A conical bullet, on the other hand, is irregular — being longer than it is wide. Instead of a ball, it’s more like a spinning top that can balance only on its point as long as it spins fast enough. The longer the bullet, the faster it has to spin to remain pointed forward in flight. This attitude is called stability. If the bullet isn’t spun fast enough to remain point-forward, it’ll wobble like a top slowing down; and the varying air pressure that’s created will quickly cause it to tumble in flight. When that happens, the bullet will stray off its straight path.

Twist rate
This is when barrel makers began to be interested in the twist rates of their rifling. Prior to this time, they simply rifled the barrel with whatever twist rate their machinery supported. It’s a fact that the Hawken brothers rifled all their plains rifles with a 1:48″ twist, regardless of what caliber they happened to be.

With conicals, though, the twist rate does matter. Too slow and the bullet tumbles. Too fast and — well, less is known about what happens when the twist rate is too fast; but in my experience, you’re never able to get the same accuracy that you can when the twist rate is just right. A rifle that puts 10 shots into a half-inch with the right twist rate and bullet may put 10 of a different bullet that’s both lighter and shorter (and therefore both moving and spinning faster) into 1.5 inches.

The length of the barrel does not change the twist rate, nor its effect on the bullet — at least not directly. But a longer barrel sometimes does increase velocity. This is always true when black powder is used and can also be true when slower-burning smokeless powders are used.

A bullet that exits the bore of a barrel (of any length) with a 1:12″ twist rate and is traveling 1,200 f.p.s. is spinning at the rate of 1,200 revolutions per second (RPS). Speed that bullet up to 2,400 f.p.s. as it leaves the muzzle, and you increase the bullet’s spin to 2,400 RPS.

If a longer barrel causes an increase in muzzle velocity, it also causes an increase in the rotation rate of the bullet once it leaves the barrel. It does not change the barrel’s twist rate; but because the bullet is going faster; it’s also spinning faster. Reloaders take that into account when they load their cartridges. It’s possible to drive certain bullets too fast or too slow, resulting in less accuracy. Reloading is about finding a balance between the bullet and the velocity at which you launch it.

The M16
The most public and classic case of twist rates and their effects was the launch of the M16 rifle to the U.S. military. It addresses the specific question that Feinwerk asked. The early developers of the 5.56mm cartridge selected a twist rate of 1:14″ because the bullet was barely stable and would tumble and destroy flesh fast when it impacted a body. But they were focused only on the cartridge’s use in Vietnam — a conflict that was mostly conducted at short range and in very warm weather. The 1:14″ twist rate was too slow to stabilize the bullet properly beyond about 250 yards or in very cold weather. It worked great for a 40-grain .224-caliber bullet moving 4,000 f.p.s. from a .220 Swift, but was horrible when used with a 52-grain .224-caliber bullet moving 3,200 f.p.s from an M16.

Don’t confuse the caliber size in inches (.224″) with the name of the cartridge. Both the .220 Swift cartridge and the 5.56mm cartridge (M16) use the same .224″ bullets.

The twist rate for the M16 was increased to 1:12 inches, which worked better, but in time even that rate was discovered to be too slow to do everything the military wanted. Today, the twist rate for an M16 variant rifle runs anywhere from 1:7″ to 1:10″…depending on the specific model of gun, when it was made, which service owns it and what kind of ammunition it’s expected to shoot.

And the answer, Feinwerk, is yes…the twist rate of centerfire rifles does vary by caliber, by the bullets used and the velocities at which they’re driven.

This first twist-rate primer report was written at a very high level. I don’t know whether or not it addresses everything you wanted to know, so I’ll read your comments with interest. If we need to go into greater detail, that’s always possible. Otherwise, I’ll remain at this overview level in the next report.