Posts Tagged ‘ballistics’
by Tom Gaylord, a.k.a. B.B. Pelletier
Before we begin, here’s an update on my good friend Earl “Mac” McDonald, who’s contributed so much to this blog and has enriched my life and the lives of many who participate here. He’s at home, being cared for around the clock by a home-care nursing staff. That will soon transition into home-based hospice care, as his condition will not improve. He knew I came to see him, and we spent a lot of time together in the two weeks I was there. If he could, he would thank everyone who’s sent him good wishes and prayers.
Today’s topic came in about a week ago, and I put it in my bank of reports to write while I’m on the road. Although today is Monday, I’m still traveling home from seeing Mac. The distance was so great that I broke it into a 3-day trip, and was planning to stop by the American Pickers store in Nashville. I got there before they opened, and hundreds of people were already waiting in line to see it. So, I decided to just continue driving home.
The question is: How did shooters of old test their trajectories? How did they know where to aim for the longer shots?
I suppose the answer breaks down in several ways. Buffalo hunters, for instance, shot just one load in their rifles so that one load was all they had to learn. The land over which they shot was mostly flat and dusty so they could see the strike of the bullets when they hit the ground. Over time, they learned where to set their sights to hit animals at different ranges, and they used the feedback they saw downrange to refine their understanding of the ballistics of their rifles.
Then, there’s the scientific approach, which is based on mathematics. Calculations can be made to predict the flight of the bullet with good precision, then they’re verified and refined by empirical testing on the range. One of the best-documented instances of this is the development of the cartridge that became the .45 Government, or what we know today as the .45-70. That cartridge started out as a .50-caliber round; but through range studies and exhaustive testing they discovered that the .45-caliber bullet had better ballistics. If you’re interested in this sort of thing, there’s a very thorough report of the entire cartridge development in M.D. (Bud) Waite and B.D. Ernst’s book, The Trapdoor Springfield.
Though the timeframe for this development was the late 1860s and early 1870s, scientists knew a lot about how projectiles flew ballistically — and they had good mathematical tables to help them with their research. Ballistics was already an established field of study when this cartridge was developed.
But what about the amateurs? What did they do? Some were able to use the same tables as the scientists, and they used their own ranges to confirm and tweak the results of the calculations. But they didn’t have Chairgun back in the 19th century, so whatever did they do?
Chairgun, and now Chairgun Pro, is an airgun and rimfire ballistics software that helps you plot the trajectory of a pellet before you shoot. It has become a great favorite of airgunners who use it to set their scopes for different ranges with different pellets. Field target competitors find it especially useful because they need to know the exact place in the trajectory their pellets will be at all ranges. Those pellets must pass through small holes in the front of the steel targets they shoot at in order to hit the triggers in the back of the targets and knock them down. If their pellet partially hits the face of the target as it passes through the hole, it can lock the target in the upright position and it won’t fall — robbing the shooter of a point. But the Chairgun software and lots of testing helps the shooter refine his pellet plot so he gets it in the right place every time.
And the good news is that now they have a version that works on Mac computers, too, so I’ll finally be able to use it!
But 150 years ago, there were far fewer personal computers — so what did those people do to determine the actual trajectories of their bullets? Well, to paraphrase the movie, The Graduate, I have two words for you — tissue paper. They lined up tissue paper screens between the muzzle and the target, and shot through them to “watch” the drop of the bullet over distance.
Now, before some wiseacre scientist in the crowd pulls the Heisenberg principle card on me, I’m aware that passing through even one sheet of tissue paper does have an effect on the ballistic flight of the bullet, however slight. I’m also aware that a bullet isn’t a subatomic particle, but I wanted to get that idea off the table so we could discuss the thing that “they” really did in order to measure the flight of bullets.
When Dr. Mann did the 37 years of work that eventually lead to his book The Bullet’s Flight, from Powder to Target, he used tissue paper screens at regular intervals between the rifle and target. He wasn’t looking for the trajectory as much as he wanted to know the attitude of the bullet at various distances from the muzzle. In his day, it was suspected that bullets left the bore unstabilized and then stabilized as they went downrange. So, he was looking for the pattern of elongated holes on the screens that would indicate yawing bullets.
How did they align the screens?
If you have ever given this approach any thought, you must have wondered how the screens were aligned. For example, if all the screens are supposed to be the same height above the ground from the muzzle to the target — how is that done? You don’t just set them on the ground and hope they line up; because no matter how flat the ground may be, there are still variations of several inches at various points along the bullet’s path. But these people wanted those tissue paper screens to be aligned within the tightest variation possible.
Today, we’d use a laser and place the screens so each one aligned with the laser’s dot; but just as computers were in short supply back then, so were lasers. So how did they do it?
They used a surveyor’s transit to align each screen. Because of the nature of what they were doing, they had to start placing screens at the target and work backwards to the gun because each screen obscured everything that was beyond it. With a laser, you work the same way. The only difference is that one person can lay out a range like this with a laser, while a transit takes at least two people. If you’ve never tried it, don’t make light of it, because you cannot imagine the difficulty of aligning all those screens. And, if the wind is blowing, you might as well give up because the screens will never settle down.
Did it work?
Some of you know this works because you’ve tried it yourselves. Yes, it does work. The tissue paper needs to be stretched tight on the screens so it doesn’t tear. That isn’t as important for firearm bullets as for airgun pellets, but the paper does need to be fairly flat for every bullet or pellet. And airgunners usually don’t need to place screens out beyond 50 yards or so, while in the past firearms shooters often placed them out several hundred yards.
For an airgun, an interval of 5 yards is useful. For firearms going out to long distances, a 25-yard spacing might work better, though closer to the gun so that spacing might be reduced to 10 yards.
A modern anecdote
In the early 1990s, several government physicists wrote papers that criticised the story of Billy Dixon, the buffalo hunter who shot an indian off his horse at 1,538 yards during the second battle of Adobe Walls, Texas. It took him 11 shots to find the range. The physicists said it wasn’t possible for a .50-caliber bullet weighing over 600 grains and leaving the muzzle at 1,250 f.p.s. to even go that far, let alone to hit a target way out there. So, several shooters convened at Fort Huachuca, Arizona, where the U.S. Army had a millimeter wave radar to track their bullets in flight.
What they learned astounded them. A bullet from Dixon’s rifle could go over 2,500 yards, and the Army’s .45 Government bullet went past 3,000 yards. Even though they were subsonic much of the way, these bullets were proven to have very great range. This experiment could not have been done with tissue paper, since the barrels had to be elevated 30 degrees to the horizon.
I hope this answers the question our reader asked about how trajectories were verified in the past.
by B.B. Pelletier
Shao Lin wins this week’s Big Shot of the Week.
The more I read the old books about shooting and guns written by men who were born in the 19th century, the more I realize how much alike we all are — and I don’t just mean shooters, now. I mean people, in general!
Let’s begin with nicknames or handles. We have some clever ones here on this blog. But are you aware that back in the late 1800s, shooters who posted letters in their favorite shooting publications — which at that time were mostly newspapers — did the same thing?
Names like Medicus and Iron Ramrod shout out from the late 19th century with their concerns that the younger shooters who are getting used to cartridge-loading breechloaders simply do not know the rudiments of shooting like the “real shooters” who grew up with black powder! The new crop of shooters (I’m speaking of late 19th-century shooters, now) have forgotten how to measure a group with string and they want to measure the distance to their targets in yards instead of rods like real shooters do.
Then, there are the experiments they performed. Dr. Mann was the great one for this, and he kept a very compliant Harry Pope busy fashioning the testbeds for his various forays into the arcane world of ballistics. Things like the cylindrical rifle action that allowed Dr. Mann to rotate the action by degrees in a complete revolution, all while the gun was safely snugged down in his 3,000-lb. “Shooting Gibralter” vise. Or the barrel he convinced Pope to rifle after drilling and tapping eight holes through the side of the barrel near the muzzle so Mann could test the effects of releasing gas to the side so it didn’t exit the muzzle with the bullet. Pope had to lay out that rifling job so those pre-drilled and threaded holes ended up in the grooves of his gain-twist rifling and did not cut through any of the eight lands!
I got a call the other day from Dennis Quackenbush, who follows my column in Shotgun News. He became interested in my comments on the rifling twist rate of airgun barrels as it relates to stabilizing those solid pellets that I call bullets. They don’t shoot very well in most airgun barrels because the twist rate of one turn in 16 inches of barrel isn’t fast enough to stabilize them once they exit the muzzle. So, he offered to make me two test barrels — one rifled 1 in 22″ and the other rifled 1 in 13″ — to test what effects the twist rate has on pellet stabilization. I’m going to accept his offer, and we’ll have yet another look at one of the big drivers of accuracy. I’ll also test velocity using the exact same power settings, so we will have a good look at how twist rates affect velocity.
Years ago, Dennis allowed me to cut off one of his smallbore CO2 rifle barrels an inch at a time so I could chronograph the pellets coming out of many different barrel lengths. I reported those results in The Airgun Letter after completing the test, which is why I now have some sense of how long a CO2 barrel needs to be to get maximum velocity.
Then, there’s the famous Cardew experiment from their book, The Airgun From Trigger to Target, where the authors fired a spring-piston rifle in an inert gas environment that didn’t support combustion — all so they could test the power level of a spring-piston rifle that was denied the possibility of dieseling. The fact that they did the experiment was good enough. We learned that all air rifles that shoot above a certain velocity diesel with every shot. But what was really cool was how they did it — by shooting inside plastic bags!
When I worked at AirForce, we had a customer who purchased a .22-caliber Condor, then proceeded to adapt the rifle’s reservoir to a large helium tank. He could then sit at a bench and fire the rifle on pure helium. He claimed to get over 1,500 f.p.s. from his modified rifle. It was useless for anything else, but he didn’t want to do anything other than see how fast it could shoot.
Even my semi-sane buddy Mac bought a 26-inch Weihrauch barrel in .177 just so he could adapt it to his son’s Condor. He was looking for a flat-shooting air rifle and I guess he got it, because his son is now supposed to be able to keep all his shots on the round end of a soda can at 80 yards.
Let us never forget the great pogostick repeating airgun! That one is now in Vince’s protective care, awaiting his verdict on whether or not it can be made operable.
Here’s a problem many shooters have. Their dominant eye is on the other side of their body from the side that dominates the motor skills. The most common is a right-handed person whose has a dominant or master left eye. This can be overcome in a number of ways — including tinkering! Back when Edith was shooting BRV, she discovered that she is left-eye dominant; but Gary Barnes, who made the rifle she competed with, made her an outrigger scope mount that put the scope in line with her left eye. The mount had to be boresighted for just one range; because like the pellet drop, the gun also shot to the left from the shooter’s perspective. No problem in BRV, though, because it was all shot at one distance.
Edith’s outrigger scope mount helped her sight with her left eye while shooting right-handed.
But Edith is far from the first shooter to have this problem. Take a look at the lengths a shotgun maker will go to satisfy his client.
A friend owns this shotgun with a crossover stock. It was made to aid a right-handed shooter who is left-eye dominant.
A couple months ago, I bought an unusual Schmidt-Rubin Model 1911 rifle at a gun show. This one has been carefully transformed into a fine target rifle. I could spend a whole blog on just this one rifle, but here are some highlights. The military stock has been completely reshaped into a target style with a deeply curved pistol grip. The bolt handle that used to be two cones of red plastic (yes, I said plastic — though they may be almost any synthetic, since this is a 1911 rifle) now has a steel ball for a pull. It looks odd but it works. And the front sight is a thing of beauty. A man has taken the time to hand-make a target globe front sight with replaceable inserts. I got only the one insert that’s in the sight now, which is two brass wires arranged like scope reticles. They look crude up close; but last week at the range I put four cast lead bullets in one inch at 100 yards, and that was the first time I ever loaded for this rifle.
Someone converted this Swiss Schmidt-Rubin model 1911 rifle into a target rifle. The stock is fashioned from the original military stock.
He replaced the conventional red synthetic bolt knobs with a steel ball, which he welded to the bolt handle.
The amount of time and care that someone put into making this target sight is amazing! This is where enthusiasts will take the sport when they have the time, motivation and skills.
I remember attending an airgun breakfast sponsored by the NRA at the Annual Meetings in Kansas City. Dennis Quackenbush and I sat on either side of the man who was the CEO of Crosman Corporation at that time. We got onto the subject of all the people who modify Crosman airguns, and the executive said he was surprised that shooters would spend time and money on a $39 airgun. Dennis told him, “Oh, but they do. You sell them the gun for $39 and I sell them $125 worth of accessories. Your guns are keeping me in business!”
From the look on the man’s face, I don’t think he believed us. And from his perspective, maybe he was right. He might sell 50,000 SSP air pistols in a year and Dennis might sell the parts to modify 500 of them in various ways. So, each man had an entirely different perspective on the situation.
As a writer, though, my eye is always on what people are doing, or what they say they want to do. I can’t be interested in a buyer who responds to a point of sale promotion at a discount store, because he may lose interest tomorrow. It’s when he finds his way to this blog through the tanglefoot of the internet and asks that first question that tells me we’re about to gain another potential member in out growing ranks. It’s at that point that my mantra becomes one of flypaper.
Almost anything can be interesting if it’s presented in the right way. And with airguns, one of the right ways is to wow the audience. Make them say to themselves, “I didn’t know that!” If you can do that, we’ll gain a lot of new shooters who are interested in learning.
Another way to attract new people is to help them through the minefield of hype and hyperbolae. The marketing people are doing all they can to attract people to the hobby, but it’s us veterans who will make things inviting enough that they’ll want to stay. And that is what I want, more than anything.
This report is going to start a controversy, because it dares to question the things that are currently held dear among airgunners and firearms shooters, alike. Sorry, but here it goes.
What is a crown?
The crown is the end of the barrel, or the place at the muzzle that has the final influence upon the bullet as it transitions to ballistic flight. One popular belief is that if the crown is not perfectly symmetrical, then one side of the pellet or bullet can exit before the other and allow escaping gas to impart a destabilizing effect on the bullet at the beginning of its path to the target. So, crowns have to be perfect, according to the vast majority of shooters.
The other side
But there have been experiments done that show that escaping gasses have zero effect on a bullet in flight. The most well-documented of these were done by Dr. F.W. Mann, who wrote about them in his book The Bullet’s Flight, From Powder to Target. Dr. Mann did numerous experiments until finally he demonstrated that a plank six inches long placed within 1/16 inch of the muzzle blast has absolutely no effect on the accuracy of a bullet.
You see, in Dr. Mann’s day riflemen believed that the muzzle blast had a deleterious effect on the flight of the bullet, and they warned shooters to keep the muzzle clear of any and all obstructions.
But is what Dr. Mann tested the same as an inaccurate crown? Maybe not. The question seems to be what, exactly, does the crown do?
The end of the rifling and the face of the muzzle bore must be as square as possible to the bore for the crown to be perfect. The reason for this is as I stated earlier — that the base of the bullet/pellet leaves the muzzle at exactly the same point around its circumference, rather than one part coming out before the rest. But there are all kinds of crowns, including some that don’t look like a crown at all.
Let’s look at some crowns now.
The crown of this Ballard target rifle is flat and polished like a mirror. The old-time shooters felt it was easier to see the distribution of the bullet lube — as it made a pattern on the face of the muzzle. There’s almost no break between the bore and the muzzle on this rifle — which is one of the more accurate ones I own. In the 135 years since this rifle was made, there has been no damage to this crown.
This Butler Creek bull barrel for a Ruger 10/22 has a recessed crown that’s similar to the Ballard crown except for the recess. However, on this one, it’s possible to see a tiny break (chamfer) at the muzzle. With the right ammunition, this rifle can hold 10 shots close to one-half inch at 50 yards. The recess supposedly protects the actual crown from inadvertent damage.
No doubt that this crown on an FWB 300 target rifle will look more familiar to most shooters. It’s the traditional rounded or radiused crown with a protected chamfer at the true muzzle. It’s on my most accurate ten-meter target rifle. Doesn’t look so pretty up close, does it?
The crown on this HW55 SF air rifle is similar to the one on the FWB 300, but up close it looks pretty disgusting. The rifle is one of the more accurate 10-meter target rifles I own. So, looks can be deceiving, and a “perfect” crown may not be all that it’s cracked up to be.
Not looking like your typical crown, this Swedish Mauser M1938 crown is a lot like the “redneck” crown job that hobbyists do on their guns. This is on a very accurate rifle. The lighting makes the bore seem to have a shoulder around the inside of the muzzle, but it doesn’t.
The redneck crown
Since the 1960s, there has been a hobbyist approach to crowning a barrel. It consists of a round-headed brass screw and a grinding compound — like automotive valve grinding compound. Chuck the screw in a hand drill and coat the domed screw head with grinding compound. Then, run the drill motor slowly while allowing the axis of the drill to oscillate to avoid making an oval cut. The result will look something like the crown on the Swedish Mauser M1938 shown above.
The crown on a custom barrel for a .17 HM2 rifle. Though brand-new and not even broken in yet, this rifle has already shot a five-shot 50-yard group that measured 3/8 inches across the centers of the widest shots. Note the powder burn pattern around the muzzle. This is the same thing that old-timers analyzed on the mirror surface of the Ballard muzzle when it was bullet lubricant that spread out instead of carbon fouling. This is another deadly accurate rifle that has no noticeable “crown” to the muzzle. The transition is very close to 90 degrees.
The crown on an AirForce Condor is very similar to the recessed target crowns shown before, except that this one has a definite chamfer or break at the muzzle. This rifle shoots half-inch five-shot groups and three-quarter inch 10-shot groups at 50 yards. And, yes, I did notice that it is time to clean this barrel!
So, what’s the verdict?
I’m not sure. That’s where I am on the whole crown issue. The reasoning makes some sense, and I can see why a PCP or a CO2 gun would then need a good crown, but a springer barely has any compressed air exiting the muzzle, so where’s the advantage there?
Don’t say anything about crowns removing burrs at the muzzle, because Dr. Mann did an extensive test in which he screwed blunt-tipped screws into the side of his Pope barrel at the muzzle to see if burrs at the muzzle that deformed bullets affected accuracy. They did not. He set his blunt-tipped screws to plough to the bottom of the grease groove of the exiting bullet, and no change was noticed in its accuracy at 100 yards.
Are crowns placebos?
I’m still undecided on the importance of crowning a barrel. I’ve read what everyone says, which is that the crown is of paramount importance to the accuracy of the barrel, yet I’m not convinced that it is. I’m also not convinced that it isn’t. I just don’t know.
I think there’s something more that has not yet been discussed about crowns and their importance to accuracy, but I’ll be darned if I know what it is. Do shooters shoot better after receiving (or doing) a crown job on a particular barrel? If you read what they write, they seem to. And most shooters believe that the barrel’s crown is of great importance to the performance of the barrel.
I wish I knew for sure, but I don’t.