Posts Tagged ‘trajectory’
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
Quackenbush .308 big bore is an attractive airgun.
The last time we looked at this Quackenbush .308 big bore was when I discovered that my rifle really likes Mr. Hollowpoint’s 68-grain hollowpoint bullet. I also tested a 150-grain Loverin-design bullet that was just a bit too heavy for the gun. It didn’t want to stabilize and was tearing elongated holes in the target at 50 yards.
If you’ll recall, I was running low on air that day, so I could fill the rifle to only 3,000 psi. That gave a stunning group that was smaller than one inch at 50 yards with the 68-grain hollowpoint, but I wondered whether it would do any better if I filled the rifle to higher pressure. I also wondered if going just a trifle faster would have stabilized the 150-grain bullet. There were a lot of unanswered questions after the last test.
Today, I’ll address those questions. I had a full air tank and a reasonably good day at the range. Certainly for testing something as stable as a .308, the light breeze was no challenge.
Shooting the 68-grain hollowpoints
I decided to fill the rifle to 3,500 psi, to see what kind of velocity that might give. The 68-grain bullet averaged 1051 f.p.s, on that much air and left about 3,100 psi in the tank for the second shot. That’s a muzzle energy of 167.15 foot-pounds.
Shot two averaged 1,010 f.p.s. with the same 68-grain bullet and generated 154.07 foot-pounds of energy. You might think that’s close enough to the first velocity that the bullets will print in the same place. They might if this was a firearm — but it’s an air rifle, and we have to take the flexing of the horizontal air reservoir into account. As the pressure inside the air reservoir changes, the reservoir — which is a long tube — flexes a tiny bit. Since it’s connected to the barrel, this flexing can cause movement in the muzzle.
The first shots printed about two inches higher on the target than the second shots. I knew they would from past experience shooting other big bores, so this came as no surprise to me. I actually shot one group of first shots (after a 3,500 psi fill) at one target and a separate group of second shots at a second target.
After seeing where the shots landed relative to the aim point, it’s possible to use the mil-dot reticle in my scope to shoot both shots into the same group by using two different aim points. This is a technique I learned several years ago with my .458 Outlaw; and with it, I can put five bullets into one inch at 50 yards. I didn’t try that on this day, however, because I was too busy learning the gun.
Neither group obtained this day was as good as the group I shot last time on just 3,000 psi of air. The first group that was shot on 3,500 psi measured 2.72 inches between centers for five shots, though four of those shots landed in a group measuring 1.219 inches.
Four of the five bullets were close at 50 yards on 3,500 psi. Two landed in the same hole.
The group that was fired on 3,100 psi measured 1.953 inches between centers. That’s twice the size of the best group that was shot several weeks ago on 3,000 psi, so I think this bullet is going too fast for best results. It looks to me like this 68-grain hollowpoint wants no more than 3,000 psi as a max charge. That would put the velocity at around 970-980 f.p.s.
Lower starting pressure gave a tighter group. This one was made with 3,100 psi.
Did the 150-grain bullets stabilize?
Again, the 150-grain bullets failed to completely stabilize — even when driven to 825 f.p.s (on 3,600 psi air) and generating 226.75 foot-pounds of energy at the muzzle.
Both bullet holes show evidence of tipping. The bullet is not stabilized.
Clearly, this Loverin bullet is too long to stabilize at the velocity this rifle generates. What’s needed is a 120- to 130-grain bullet that’s short, which means it must have either a round or a flat nose.
I’m seeing a relationship between soft pure lead bullets and better accuracy. Any hardening alloy seems to open up the group.
Ditto for lubricated bullets. So far, the best, most accurate bullets are those that are completely dry. I see now that I need to cast some more 130-grain bullets in lead that is as pure as I can make it, and shoot them absolutely dry. I’ve seen the performance of pure lead bullets on game, and they hold together far better than hard alloy bullets do. Lead hardened with antimony breaks apart in large chunks, while soft lead mashes up like a wad of bubble gum when it hits game.
I’ve always questioned using a .308 for game as large as a deer. I know hunters who are better shots than I am do it all the time and have great success, but for me the .308 is more of a coyote and bobcat round. I’ll leave the deer and wild hogs to the .458 and keep this .308 for smaller game. It probably has a useful range of 125 yards in my hands. For an air rifle, that’s pretty far!
by B.B. Pelletier
Tyrone Nerdin’ Day says this about his winning photo: Me and my IZH-DROZD MP-661k Blackbird with Wild Mod Chip, Walther PS 22 red dot sight, quad rails and a UTG Tactical Op bipod. Black SWAT vest with the Walther CP99 Compact, police belt with Winchester Model 11.
Quackenbush .308 big bore is an attractive air rifle.
It’s been a long time since Part 2 because I was searching for a better bullet for this rifle. Oh, the groups shown in Part 2 aren’t that bad; but when you see what I have to show today, you’ll be glad I stuck with it.
Most of my experience has been with Quackenbush’s larger calibers. My Quackenbush .458 Long Action rifle is so accurate that I was pretty sure I could get better performance out of this .308.
The .308 is the big bore gun everyone talks about these days. Guys are taking deer and goats with them out to incredible distances. At the 2012 LASSO big bore shoot, they were hitting half-sized sheep silhouettes out to 300 yards and making it look easy. But the bullets I had didn’t seem to want to perform like what I saw from other guns. So, I kept searching and trying different bullets.
Blog reader Robert from Arcade even sent me a batch of 150-grain Loverin-style lead bullets he cast himself. They were big and heavy, and my rifle wasn’t doing that well with lighter lead bullets, so I didn’t have a lot of hope for these. But I took them along to the range yesterday, where I tried them along with a remarkable new bullet that I picked up at the Arkansas airgun show this year.
Mr. Hollowpoint saves the day!
At that show, I asked Robert Vogel, who’s Mr. Hollowpoint, for a good bullet for my rifle. He recommended a new hollowpoint he’s casting that has had some good reports. At 68 grains, it’s a featherweight compared to the 115 to 130-grain bullets I’ve been shooting, and I thought maybe the additional velocity I’d get might make the difference. So, I bought a bag to try.
I got out to the range on Wednesday, and the day was very close to perfect. At 88 deg. F, it was a bit warm, but the wind was very low and never did pick up.
The 150-grain Loverin bullet on the left and the 68-grain hollowpoint at the center and right were both tried. Notice the uneven base on the hollowpoint. It seemed to make no difference on the target. That large hollow point lives up to its name!
My carbon fiber tank would soon need a refill, so I was only able to fill the rifle to 3,000 psi, and I held the number of shots per group to 5 instead of 10. The first shot was low and about three inches to the right of the bull, so I cranked up the elevation and put in some left clicks and then shot a 10. It was nothing but luck that the one adjustment put the bullet in the right spot.
It doesn’t get much better than that, so I refilled the rifle and shot again. I was filling after each shot, so every shot had the benefit of a 3,000 psi fill behind it. With the Quackenbush Long Action Outlaw, and to a large extent with all other big bore air rifles I’ve tested, the first and second shots group in different areas — but they do group tight. The trick is to use some extra elevation for the second shot so it goes to the same place as the first. But since I didn’t know exactly how much elevation to use with this new bullet, I refilled after each shot instead.
It was a slow, methodical process of settling into the rest, sighting, squeezing off the shot, then returning to the tailgate of my truck to top off the reservoir for the next shot. My shooting buddy, who witnessed all this, was impressed by how much recoil this .308 has. Of course, it recoils with or without the bullet, because the air that’s exhausting is giving the rifle a rocket push.
By the time the fifth shot had been fired, I could see the results through the scope. The group was tight and well-centered, and the last three shots were in the x-ring, which is in the center of the 10. They can be covered by a dime. So, this 68-grain hollowpoint from Mr. Hollowpoint is the bullet my .308 likes!
Five shots went into this 0.975-inch group at 50 yards. The 68-grain bullets from Mr. Hollowpoint are a real winner in my Quackenbush .308. The center three bullet holes can just be covered by the dime.
The base of the bullet has an uneven ridge extending past the base. It’s the result of sizing the bullet, because Robert Vogel sizes each and every one to .308. Normally, I would worry about anything on the base that isn’t perfectly uniform; but after looking at the target, I can see that this has little affect on how this particular bullet flies.
This bullet loads very easily in my rifle. There seems to be no resistance when the bolt is closed. They’re cast from pure lead, which leaves them soft and prone to deformation. Performance on game is enhanced through the combination of the soft lead and the hollowpoint design. A soft lead bullet holds together better than one that’s hardened with antimony, so these bullets still penetrate deeply in game. Elmer Keith wrote extensively about the performance of soft lead bullets on game with handguns, and the velocity of these big bore rifles is pretty close to what he obtained.
I wouldn’t use such a light hollowpoint on a whitetail deer-sized animal, but it ought to turn a coyote or a bobcat inside-out! And the rifle is now zeroed at 50 yards — huzzah!
From light to heavy
Next up was the Loverin-style 150-grainer from Robert of Arcade. Since the rifle was only so-so with the lighter bullets I’d tried, I didn’t think it would stabilize this long lead slug, but it wasn’t much trouble to try. Robert also casts these from lead as pure as he can get; so, like Mr. Hollowpoint bullets, they’re just right for airguns.
A Loverin bullet has many grease grooves along a relatively long body. It was greatly in favor in the early 20th century. When jacketed bullets came along, they sent the best lead bullet designs into relative obscurity. Only those who cast their own bullets are aware of the differences in designs like the Loverin, and this style bullet is no longer popular with mold-makers today. If I want to get a Loverin mold, I either have to buy a custom mold or I have to watch the auction sites for a vintage mold to come up for sale. This one is Lyman mold 311466.
In contrast to the easy loading of the 68-grain hollowpoint, these bullets were hard to load. They were not sized and measure up to 0.311 inches in diameter. I normally shoot unsized lead bullets in my big bores whenever I can to ensure the best sealing of the bore — a little resistance at loading is normal.
The bullets landed lower on the target, as expected, and they were about a half-inch to the right; but after 5 shots, I was impressed by the group they made.
By this point, the carbon fiber tank was definitely running out of air. On the final two shots, it filled the rifle to only 2,950 psi. Since the resulting group seems elongated up and down, I will attribute some of that to the uneven fill. I think that if I shot this bullet at a higher-pressure fill, the performance might improve.
Notice, also, that the bullet holes seem elongated. There was some tipping going on, and this bullet is probably at the ragged edge of stability at this velocity — whatever that is. A higher-pressure fill will probably boost velocity enough to correct this at 50 yards.
Five shots went into this 2.008-inch group at 50 yards. The Loverin-design bullet did remarkably well, considering its 150-grain weight. The last two fills were only 2,950 psi. I wonder what a higher, more uniform fill might do?
This longer, heavier bullet would be ideal for deer. While the velocity is probably down at the 700 f.p.s. mark, these bullets still shoot all the way through deer unless they’re stopped by heavy bone. I would restrict my shots to very close range with this bullet, but I think it might do the trick out to 80 yards, or so.
Now that I have one good bullet for sure and the possibility of another, it’s time to test both with higher fill levels. I also want to chronograph these bullets so we can see what sort of performance they give.
I also want to cast some of my 130-grain spitzers in pure lead and shoot them unsized and unlubricated. That might be the secret to success in this rifle.
We’re not quite done with the Quackenbush .308. My thanks to both Mr. Hollowpoint and to Robert from Arcade for providing me with these two bullets to test.
by B.B. Pelletier
This report is in response to a comment Pyramyd Air got from a customer who doubts that fixed-barrel airguns can ever droop. His position is that they can only have droop if the barrel is heated in some way (as on a firearm that fires very fast) or if the gun is assembled in a shoddy fashion.
He said he believed barrel droop is only commonly found on breakbarrel airguns, which is why he said he would never own one. He thought that droop was mostly caused by the metallurgy of the barrel.
Today, I’d like to address the subject of barrel droop in detail. It can be caused by many things, but poor metallurgy isn’t one of them. Barrels do not bend from cocking, despite what some people may think. It is true that a barrel can be bent by human force, but the force required to do so is much greater than the heaviest cocking effort on the most powerful magnum airgun. So, poor metallurgy is not a contributor to barrel droop.
What is barrel droop?
I will explain what barrel droop is in detail later in this report. For now, I’ll just say that barrel droop is a condition in which an air rifle shoots so low that the scope cannot be adjusted to hit the target.
You must understand that most scopes cannot be adjusted all the way to their highest elevation settings and still operate correctly. This will differ from scope to scope, but generally most scopes do not work well when adjusted above three-fourths of their maximum elevation. It’s imperative that they get on target before reaching that height, and a drooping barrel can prevent that.
Throughout the first five decades of spring-piston air rifles, no one ever heard of barrel droop. It was a non-issue. That was because nobody bothered scoping their air rifles.
The sights on most breakbarrel guns are attached to the barrel, both at the front and rear, so they’re in line with the bore — as long as the bore is drilled straight through the barrel, which it seldom is. The amount of misalignment is usually measured in the thousandths of an inch — an amount the sights can easily account for.
With both the front and rear sight attached to the barrel, there’s less chance for misalignment.
In the 1960s, retailers began attaching scopes to airguns to sell more of them. Firearms had been using scopes for some time, and the general belief among shooters was that scopes extracted the maximum accuracy from any gun.
But scopes had a problem, as well. They were attached to the spring tube of the gun, which isn’t integral with the barrel on a breakbarrel airgun. For the first time, the alignment of the spring tube and barrel came into question.
It soon became known that most breakbarrel guns have a barrel that slants downward from the axis of the spring tube. In the 1960s and ’70s, breakbarrels were hand-selected for scope use when they exhibited less slant than other guns of the same model. You can read about this selection program in both the Air Rifle Headquarters and Beeman catalogs of the period.
What those catalogs didn’t address was the fact that fixed-barrel airguns can and do sometimes have the same barrel slanting problems. They didn’t address it because, at the time, scoping airguns was brand new and not that much was known about it. The people scoping the guns often installed simple fixes, such as shimming the rear ring, and didn’t even think about why they were doing it.
Why the barrel droops
The comment that prompted this blog went on to say that barrel droop was caused by poor metallurgy. Evidently, the writer thought that “droop” referred to a barrel that was curved (or bent) downward — which is not the case. The term “droop” doesn’t refer to a barrel that is somehow curved. It means a barrel that points in a direction away from the sight line, so the axis of the bore and the sight line are diverging. To correct for this droop, the scope has to be repositioned to align with the axis of the bore.
We all understand that a pellet starts falling the moment it leaves the muzzle. The farther from the muzzle it goes, the faster it falls; so the line of flight is actually an arc, rather than a straight line. To align the sight line of the scope with the axis of the bore, we have to align the scope to look downward through the line of flight. To be effective — that is to get any distance over which the pellet is on target — the sight line is made to pass through the arc of the pellet twice — once when the pellet is close to the gun and again when it’s farther away.
The scope is angled down through the pellet’s trajectory. This illustration is greatly enhanced for clarity. This alignment is done the same for firearms and airguns, alike.
But the question is, “Why does the barrel point downward?” With a breakbarrel, it’s usually because of how the breech locks up at a slight angle that causes the downward slant. Some guns, most notably target breakbarrels, overcome this with barrel locks that cam the breech tightly against the spring tube in a straight line. Most guns rely on the spring-loaded detent to both align and hold the barrel during firing. If there’s a weakness, it’s at this point. When a breakbarrel with an unlocked breech fires, the barrel tends to flex in the direction the barrel is hinged. If the barrel broke upward to cock, the problem would be reversed and we would have a barrel “climb” problem.
A breech lock like the one on this HW 55 ensures that the barrel always aligns with the sights — provided the rifle is designed that way.
Do you now understand that the barrels are perfectly straight, and it’s just the angle of the bore’s axis relative to the line of sight that creates the drooping problem? Good, because that’ll make the following easier to understand.
What about underlevers and sidelevers with fixed barrels?
How can a fixed-barrel rifle have droop? Easy — the barrel isn’t attached to the gun with the bore parallel to the line of sight. Presto! Automatic sighting problem. Or the scope base that’s attached to the spring tube may not be aligned with the axis of the bore. Or the bore may be drilled off-center; and although the outside of the barrel is parallel to the sight line, the bore’s axis isn’t. Any of these three things can happen.
Bore not drilled straight
This is very common. It’s extremely difficult to drill a deep (long) hole straight through a steel bar. The drill bit can wander off-axis as it bites its way through the steel, or it can be off-axis all the way through the bore if it isn’t correctly set into the holding fixture before the drilling begins. I’ve had barrels with bores as much as a quarter-inch off-axis with the outside. Granted that’s extreme and uncommon, but it demonstrates the possibility.
The only way a barrel-maker can ensure concentricity of the bore to the outside of the barrel is to machine the outside of the barrel after the gun is rifled.
Barrel isn’t aligned with the spring tube
This problem is also common. When the barrel is pressed into the spring tube (usually into a block that’s held in the front of the spring tube), the bore isn’t aligned with the spring tube. You might think that modern manufacturing processes make perfect things time after time, but the truth is that there’s always some variation.
Scope base on top of the spring tube is not aligned with the bore
Of all the problems with scope alignment, this one is the most common. Off-axis bores are usually held to just a few fractions of an inch for which the scope adjustments can easily compensate. The same is true for barrels that are bushed off-axis. But scope bases are both short as well as attached in such a way (by spot-welds and rivets) that precision is difficult to maintain. Because scope bases are short, any small deviation in their positioning is exaggerated when extended out to infinity by a scope’s sight line. This is the one place where firearms and certain brands of airguns have an advantage over other brands, because they machine their scope bases into the receiver (of a firearm) or scope tube, rather than riveting or spot-welding the base to the scope tube. If the tooling is set correctly, the machining process ensures alignment of the scope base.
Talking about the spot-welded and riveted scope bases brings us to a discussion of one well-known company that makes highly regarded spring-piston air rifles. This company stands head and shoulders above the others when it comes to having barrel droop — both with their breakbarrels and their fixed-barrel air rifles. That company is Diana. Historically, enough Diana air rifles have had barrel droop so severe that special corrective scope mounts have been made and successfully marketed for their models. Even RWS, who exports Diana airguns, has marketed such a corrective scope mount.
But even Diana can change. Their most recent breakbarrel is their 350 magnum model in all of its various forms, and this rifle is very noticeably immune to the drooping problem. Something has changed at Diana. I would think that, over time, we’ll see this change spread to all of their models.
Firearms also have droop
Drooping isn’t just an airgun problem. Firearms have droop, too. But because of how firearms were scoped in the early days, nobody noticed the problem.
When firearms were scoped back in the 1940s and ’50s, many of them did not have optional scope mounts available. It was very common back then for a gunsmith to drill-and-tap holes into the firearm to accept scope base screws. Naturally, when a gunsmith did the job, he would align the holes in the scope mounts so the axis of the barrel was in line with the sight line seen through the scope. If there was any barrel droop, it was corrected as the mounts were installed.
Do barrels only droop (slant down)?
Before someone asks the obvious question, I’ll address it. Yes, there are airguns with barrels that slant up, plus point to the left and to the right too much for the scope to compensate. They’re not encountered as often as droopers, but they’re not unheard of. The reasons for most of these problems are the same as for droopers except for one standout reason.
If a breakbarrel rifle has been fired with the barrel open, so the barrel was allowed to snap closed from the force of the mainspring, that rifle will have a bent barrel. The barrel will be bent upward at the point it emerges from the baseblock, which is the piece that holds the barrel in the action. It’s where the pivot bolt attaches. It’s the blocky-looking piece the barrel is coming out of in both photos of guns in this report.
For this type of problem, the solution is to bend the barrel straight again. Any qualified airgunsmith should be able to straighten a barrel that has this problem, and a number of owners have learned to straighten their own bent barrels..
Most airgun barrels don’t droop
To put this report into the proper perspective, I should mention that a drooping barrel isn’t that common. I have several air rifles whose barrels are okay for shooting with scopes as they came from the factory. And, of the hundreds of rifles I test, only a small percent have a drooping problem. So, it isn’t a given that your rifle will droop.
But you may get a drooper, and you can rest assured that there are plenty of solutions to rectify the situation should you encounter it. The things to remember are:
Not all breakbarrels droop. Only a small percentage do these days.
Rifles with fixed barrels can also have droop, for the reasons mentioned in this report. It is not as common to find a fixed barrel with droop, but any air rifle that has a separate scope base that’s either spot-welded or riveted in place is a likely candidate for droop.
Firearms have droop, just like airguns. But the amount of droop is small enough that it’s corrected by the scope or by the mounts that are supplied by the firearms manufacturers.
by B.B. Pelletier
Quackenbush .308 is handsome even in this lowest-grade version.
Today’s report will be quite different from the norm. This is Part 2, which is normally where I test velocity. I did that, and you’ll see it in today’s report — but you’ll also see some targets, because I tested accuracy, too.
When I test a smallbore pellet gun, I know at the start how the gun should perform, more or less. Yes, there are some surprises; and yes, I do make some mistakes — but a lot of what happens can be predicted pretty accurately. But not a big bore!
With a big bore airgun, I’m almost starting from scratch. Sometimes, I will have tested something similar and can use that experience as a starting point, and there’s some of that in today’s report; but this .308 rifle is unlike any other big bore air rifle I’ve ever tested. There are more .308 lead bullet designs and bullet molds available than there are .177 pellet types on the market. Out of all that, I have to select some designs that make sense.
This is where my firearms experience comes in handy, and this is the reason I often run reports on firearms in this blog: learning the intricacies of this Quackenbush rifle is exactly like figuring out how a new black powder rifle operates. And I don’t mean some ultra-modern, bolt-action black powder rifle that uses replica powders in pellet form, either. I mean a real black powder rifle made by hand and has to be figured out as you go.
So, how do you start testing a gun when you don’t know much about it? Well, you start with what you do know and go from there.
I know that other Quackenbush Long Action Outlaw guns operate at pressures above 3,000 psi, so I’ll start with a higher fill pressure. I know that this rifle will be in the 200-250 foot-pound range with bullets it can stabilize, so I’ll select them first. I know that by reading what others have written about their .308 rifles.
I also know that Quackenbush rifles have to break in. They do get faster with use. So, I’ll look for that.
Furthermore, since this is a big bore air rifle operating at a very high level of performance, it’s going to use a lot of air. I know how much air the Korean guns like the .50-caliber Dragon Claw use, and I know that this rifle is going to use even more. So, even an 88 cubic-foot carbon fiber air tank is going to get drained in a hurry.
I cast bullets for many of my firearms, and I also happen to own a bullet mold for a nice spitzer (pointed) lead bullet that was designed for the M1 Carbine. It casts at around 130 grains, which is an ideal weight for this rifle, because the expected velocity (derived from the known power that has been published by other .308 owners) will be 850-950 f.p.s. on the first shot. I calculate this velocity range by taking the expected power (say 225 foot-pounds) and running it through the Pyramyd Air velocity calculator (use the second formula on the page to do this).
The issue here is bullet stability. These bullets are stabilized primarily by the spin imparted by the rifling in the gun. The longer a bullet becomes, the faster it must spin in order to stabilize. Since you cannot change the twist rate of the barrel, you have to drive the bullet faster to stabilize it. Sometimes, though, you’ll get away with shooting targets that aren’t too far away with a longer bullet. The bullet will be semi-stable for the first 40-50 yards or so. It all depends on the bullet’s length.
The bullets I shot are like the one at the center of this photo. At the right is that same bullet with the lubricant wiped off. At the left is a 170-grain lead bullet that’s normally too heavy for this rifle. However, for close work, it might work okay. That bullet normally takes a copper gas check, but it can be shot without one.
That velocity will give a fairly flat trajectory and stability to the 130-grain bullet as far as the rifle can be accurately shot — which is about 200 yards. But consider this: this bullet is just one of over 200 different lead bullets that are appropriate for this rifle! If you really want to experiment and push the envelope, that number grows to over 500! Nothing guarantees that this will be the one right bullet. It’s just the first one I tested.
Before I went to the range, I mounted a scope on the rifle. I encountered problems right away because of how far the Weaver bases are set apart on the rifle’s action. They are so far apart that I cannot mount the leapers long eye relief scope I had planned to use, because the ring separation exceeds the scope’s tube length. This is where it gets dicey because of the scopes that were available; and the Weaver rings I had that were not committed to other tests and guns. I ended up with a set of high rings and an Osprey 2.5-10×40 scope that I don’t care for. More on that, later.
So, I get to the range and the day is pretty good. The wind is fairly calm, with just a few breezes I can wait out. Besides, I’m shooting a .308 130-grain bullet at 50 yards. The wind doesn’t affect it nearly as much as it would a pellet!
The gun’s first fill is a guess. I know my .458 Outlaw likes a 3,500 psi fill, so I go with 3,600 psi for this one. I’m looking for a couple things. First, how fast does the first shot go? Second, how fast do shots two through whatever go? That’s right — I don’t even know how many powerful shots I’m going to get from this rifle. If it were a 9mm Korean gun, that number would be 5-7. But a Quackenbush .308 is more powerful and uses a lot more air. My .458 gets two good shots per fill, so there’s a very good chance this one will, too.
Before I left the house, I oiled the striker (hammer) with high-tech gun oil. I oiled it again at the range. I know that all big bore guns need to break in to shoot their best. Then, I filled the rifle to 3,600 psi and started shooting:
The first few shots were over the chronograph. Then, I commenced shooting for accuracy at 50 yards. You can see how high the scope sits above the receiver.
Okay, those are the first four shots. If I’m looking for good groups at 50 yards with this bullet, only the first two shots look good. If I’m demonstrating the rifle to a bunch of Boy Scouts, I can probably continue shooting for another couple shots. Do you see what I’m doing? I’m calculating things based on what kind of shooting I expect to do.
And shot one generates 212.06 foot-pounds of muzzle energy. Shot two makes 192.26 foot-pounds.
I also noted that when I went to fill the reservoir again, the gun still had about 1,900 psi inside. Four shots used up 1,700 psi, or about 425 psi per shot. The Korean big bores use around 200 psi per shot, so that gives you a good idea of how they compare to a Quackenbush Long Action.
Next, I sighted-in the rifle. Because the Quackenbush Long Action does not allow the bolt to be removed easily at the range, I used a target paper that’s two feet by four feet. The point of aim is close to the center of the paper. That gives me a good chance of striking somewhere on the paper at 50 yards. If this were a smallbore airgun, I would have started at 10 feet, as I explain in my article about sighting in a scope; but you can’t do that with a gun this powerful unless you own a lot of private land. I’m on a club-run rifle range, and I have to obey their regulations. I’m hoping to get on paper without boresighting. I do own a boresight device, but it has only bore spuds that go up to .22 caliber, so it wouldn’t work in a .308.
I’m in luck, because the first shot hits the paper…about two feet below my aim point. Well, that isn’t as lucky as you might think. Remember the Osprey scope I mentioned earlier? Well, it has 1/8 MOA (minute of angle) adjustments. At 50 yards, every click will move the strike of the round about one-sixteenth of an inch! For two feet, I’ll have to move the elevation knob up 16 x 12 x two, which is 384 clicks! There probably aren’t that many clicks in this scope, plus I don’t know how far up it already is. I have a droop problem!
I’ll replace this scope and mounts for the next test, which means I’ll have to sight-in and do this all over again. But today is not lost. I can still continue to test the gun. I adjust the scope up so the round lands about 14 inches below the aim point, and that’s how I will test the gun today. It’s simple enough to staple two targets to the backer in line with one another, so I can aim at the top one and hit the lower one. Now, we can see how this rifle shoots with this bullet.
The only problem is — all I have are bullets that have been sized and lubricated. I know that Quackenbush big bores seem to do best with dry lead bullets, or at least that’s been my experience up until now, but I’ll use the bullets I have on hand. I will have to cast some more bullets and not lubricate them for the next test.
Shot one went about 14 inches below the point of aim, as mentioned already. Shot two dropped another several inches, but I compensated for it by using the tip of the bottom fat vertical duplex reticle line as a different aim point. So, I’m able to get a fair grouping of bullets, though it’s nothing I am satisfied with, yet. I’m able to shoot six bullets into a group measuring 1.6 inches by shooting just two shots per fill and using the two aim points. After shot two, the gun’s remaining pressure is about 2,700 psi, so the first two shots use about 900 psi — which works out to 450 psi per shot. Do you see how this stuff works?
Two bullets in the hole on the left, and you can see the rest. Three of them were first shots after a fill, and three were second shots. This group measures 1.6 inches between centers.
I then moved over to another set of targets and tried something different. I tried refilling after the first shot — so every shot would be going the same speed and I could use the same aim point. This time, four of the five shots grouped into 0.982 inches, but the fifth shot opened it to 1.767 inches. It looked like it was going to be better, but once again, no cigar.
There are three bullets in the large hole on the left. Shot four (top) opened the group to just under one inch, but the fifth shot opened the group to almost 1.75 inches.
After shooting at two different targets, I lubricated the striker again and chronographed the gun. This time, I tried to fill the reservoir higher than 3,600 psi, but my carbon fiber tank had already dropped to 3,600 psi. I had to stick with that as the highest fill pressure.
As you can see by comparing this second string to the first one, my rifle seems to be performing at the same level, more or less. That does not tell me whether 3,600 psi is the highest operating pressure or not, but it’s a good indication that the rifle either needs a lot more shots through it or it’s already broken in. I’ll have to get my carbon fiber tank refilled before I can conduct another test at a higher fill pressure.
And just for continuity, the first shot generated 217.04 foot-pounds. Shot two generated 193.67 foot-pounds.
Where to next?
If you’re as curious as I am, these results open up a lot of possibilities. For starters I want to test the gun at a higher fill pressure. I also want to shoot dry bullets, but I think I need to clean and dry the bore before I do. I can’t clean the lubricated bullets well enough to consider them dry, so I have to cast another batch.
I definitely have to mount a different scope in lower rings, and I have to be prepared to elevate the rear mount if the rifle turns out to be a drooper. All I know at this point is that I had the scope adjusted very high, which very well could have lead to the groups being as large as they were.
I have a feeling that this rifle will shoot groups smaller than one inch once I learn its secrets.