Posts Tagged ‘droop mount’
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
Today, I’ll report on the Hatsan 125TH’s accuracy using open sights. It was a day of learning the rifle, and a lot was discovered. In the next report, I’ll mount the scope that comes with the rifle and test it again. But today it’s open sights all the way. When you read tomorrow’s report, you’ll understand how appropriate this test is.
The 125TH has a post-and-bead sight with TruGlo fiberoptic inserts. Fiberoptics are a poor choice for precision shooting because they cover too much of the target to aim precisely; but when you shoot outdoors on a bright day, they’re quick to acquire. Out to 25 yards, they’re adequate; but never choose them for long-range shooting or for hunting in the woods.
The rear notch on the 125TH is too small for the size of the front bead — hence I found it difficult to see any light on either side of the post when sighting. I also discovered that the barrel is drooping quite a lot; because even with the rear sight adjusted as high as it will go, I was still shooting below the aim point at 25 yards. That won’t get any better at longer distances, either. So, I think a scope will be better if I can get it to accommodate the droop as much as I need.
The first pellet I tested for accuracy was the Beeman Kodiak. I selected them because I knew they wouldn’t break the sound barrier, and I was shooting inside the house. The distance was 25 yards, and I used a 10-meter pistol target. The hold was at 6 o’clock on the bull. The first group was the best one of the day. It won’t look that good to you, but I learned a lot from it.
The group was 1.272 inches between centers, but it was taller than it was wide. The width is only 0.956 inches. This a characteristic that holds throughout this session.
Pellets that didn’t work
I tried JSB Exact 8.4-grain domes that went supersonic, but they were not grouping well. And Air Arms domes that also weigh 8.4 grains are equally bad. Both pellets broke the sound barrier and gave quite a crack as they went downrange.
The absolute worst pellet of all was the H&N Rabbit Magnum II. For starters, it’s designed with straight walls, so you can’t load it into the breech of a breakbarrel. You have to have something to press it in because your thumb isn’t hard enough to push it to engrave the rifling on the sides of the pellet. But I knew that going in. The first shot was about four inches higher on the target than any other pellet, and I hoped that I had found the miracle pellet for this rifle. Alas, the second pellet dropped about a foot (12 inches) at 25 yards, went through the reflector of my spotlight and popped the light bulb! Needless to say, I stopped shooting those pellets at that point.
Crosman Premier heavies
I figured the 10.5-grain Crosman Premier heavy pellet might do well, so I gave it a try. They grouped in 2.111 inches overall, but side-to-side the group was just 1.34 inches. Again, the group was taller than wide. I’m tempted to try this pellet again when the rifle is scoped.
I tried a different hold with the Kodiaks that were the most accurate pellet to this point. This time the group measured 1.71 inches between centers, but the width was only 1.152 inches. Again, taller than wide.
So, the hold didn’t improve things, but it’s now clear that the open sights are causing the problem. I’m not getting enough precision in the vertical orientation, which is why all the groups are significantly taller than they are wide. That means using a scope should show a marked improvement.
How the rifle feels
Whoever suggested trying to pull up on the trigger blade — I can’t do it because the thumbhole stock forces my hand to pull the trigger straight back. And the trigger is too heavy for good work. While there’s no creep in the second stage, there’s considerable travel that can be felt. I have the trigger adjusted as light as it will go, so this is a detractor.
The SAS works very well. I can feel some vibration with the shot, but it dies quickly, which must be attributed to the SAS.
The rifle recoils heavily. But it also rests very well on the flat of the hand, so it isn’t difficult to shoot. The best hold point is with the off hand touching the front of the triggerguard.
If the trigger were lighter, this rifle would be a pleasure to shoot. I’m getting used to the cocking effort needed, and I can’t wait to see how the rifle does with a scope.
A good day!
You might feel from these targets that I had a bad day, but with what I learned about the rifle I think I had a very good day. Next time, I’ll know two pellets to try going into the test, and I’ll also know the best hold to use. Until I did the pellet velocity versus accuracy test a couple weeks ago, I wouldn’t have known that it’s harmonics and not velocity that opens these groups. Let’s see what I can do with that newfound knowledge.
What is it?
Can any reader identify the tool in the photo below, and tell us what is it used for? It will play a part in an upcoming blog.
What is it?
by B.B. Pelletier
Announcement: Around 10 or 11pm tonight (12/15/11) Eastern time, the server for all of Airgun Academy (including this blog) will be restarted. Hopefully, it’ll be unnoticed and everything will march along just fine. If something does go wrong and everything goes offline for a while, please know that people are working on it.
Here we go! Today is accuracy day for the .25-caliber Beeman RX-2 Elite series combo air rifle. Before I start shooting groups, though, I thought I would adjust the trigger. In Part 2, blog reader SpringGunner commented that the screw inside the trigger blade is what determines the location of stage two. It’s a very small Allen screw, and the one in the test gun is so deep inside its hole that it can’t be seen.
I started by turning this screw counter-clockwise about a turn and a half, but all that did was lose the second stage for me. What I ended up with was a single-stage pull with lots of creep and an indeterminate and extremely light release. I came back clockwise on the screw about a third of the way and voila — stage two reappeared! When it did, I made certain that it was positive and repeatable before accepting the adjustment.
The trigger now breaks cleanly at 1 lb., 9 ozs. The second-stage creep is gone, and the trigger is much crisper now. While it’s still not quite as good as a Rekord, it is much better than I reported in Part 2. It’s more than adequate for hunting and occasional target work.
I noticed at sight-in that the rifle has a lot of barrel droop. Pyramyd Air had shimmed the rear scope mount, but I think I would want to use something like the BKL Drop Compensating mount to get the scope in the center of the adjustment range.
What’s in a name
And before I move on, I would like to say something about product naming and why it’s so difficult to find things on a website. BKL has named their mounts “drop” compensators, but the most common term among airgunners is “droop.” Some people think that spelling or naming a product doesn’t matter, but on the internet it matters a lot. When I searched for a BKL mount that compensated for droop, I entered the word droop in the search window and came up with all the drooper mounts except those made by BKL. Then, I happened to remember that BKL uses the term drop instead of droop, and I was able to find all their drooper mounts. [Note from Edith: I fixed it so a search for droop will now bring up the BKL drop-compensating mounts.]
Several years ago, I had an ongoing conversation with Crosman about the use of the term soft air for their airsoft line of guns. We went back and forth for five years about this until one day their VP of sales told me they just liked the term soft air better. So, I challenged him to do a Google search for airsoft and again for soft air. Soft air turned up just over three hundred thousand hits. Airsoft turned in over 15 million! Today they call all their current 6mm guns airsoft.
When the world is looking for something today, it uses an internet search engine. If you don’t call your product what everybody else calls it, expect to be excluded from the party. End of sermon.
Back to the RX-2
Sight-in went pretty quickly, and then I up to the 25-yard line. The first pellet to be tried was the Benjamin dome that did so well at 50 yards in the AirForce TalonP pistol test. But in the RX-2 it didn’t do as well. I tried a number of different holds, but the results were always the same — an open group. Since this rifle is difficult to cock, I decided to move on to the JSB Exact King.
Success with this new .25-caliber pellet was immediate. Among the four pellets I tested, the Kings were the best. The first group was very tight but had two pellets that went above the main group. I hesitate to call them fliers. They were due to a subtle shift in how I held the rifle, and the second time I knew the shot was going to move from the main group. I didn’t know that it would group with the other stray, but I must have repeated the same hold for those two shots.
Eight pellets made the lower group that measures 0.563 inches between centers. These .25-caliber pellets make huge holes and the groups appear larger than they are. Notice that the other two shots are also tightly grouped.
This target showed me two very important things about the RX-2. The first was that the huge .25-caliber pellets make big holes in the paper — groups that appear larger than they are.
The second thing I learned is that the RX-2 is very sensitive to hold. It doesn’t seem to want to be held as lightly as many other accurate spring rifles. But it does want to be absolutely “dead” weight in your hands. This means stretching the off hand out until the cocking slot is touching your palm. The rifle then sinks into your palm, and that pushes the buttpad back into your shoulder — you can’t avoid it. It’s a tighter artillery hold than I would normally use, but it works with this rifle.
More pellets tested
Next, I loaded some RWS Superdomes and noted that, of all the pellets I tested, these loaded the easiest. All other pellets were hard to push into the breech, with Benjamin Domes being hardest of all. But Superdomes went in rather easily.
Downrange, however, they scattered everywhere. No matter how I held the rifle, they never went to the same place twice. I was worried that I might shoot out of the pellet trap so I stopped. I think this pellet is better-suited to precharged rifles and not spring-piston guns — at least not the RX-2.
Then, I tried the H&N Baracuda pellet. These required a different hold than the JSB Exact Kings, but they showed some promise. However, as I was attempting to shoot a 10-shot group, I inadvertently held the forearm slightly wrong and blew the group with two shots. I think I got cocky because of the early success and didn’t pay as much attention to the hold as I should have. Instead of shooting another group of these, I opted for one more round of JSB Exact Kings, which had already proven quite accurate.
Five H&N Baracudas went into a nice cluster at 25 yards, then a small change of hold sent two pellets elsewhere. I decided to stop shooting this group and move on. The five closest holes measure 0.592 inches between centers.
One more pellet you should try with this rifle is the H&N Field Target Trophy. I didn’t test them, but several readers mentioned that they are very accurate with this rifle. And, at just over 20 grains, they’ll also have good velocity!
Another observation is that the rifle is starting to cock smoother, if not exactly easier. I think the RX-2 might be one of those rifles that needs a good period of break-in, which I have not provided in this test. Certainly from what I read on the internet, the owners of the gun seem to like it a lot and are very faithful to the model. It may even be that breaking it in will show a gain in velocity over the numbers you saw in Part 2.
The bottom line
The Beeman RX-2 is a big spring rifle that has good power. In .25 caliber, it performed better than any .25-caliber spring rifle I’ve tested recently. Part of that is due to the excellent JSB Exact King pellet, but part must also go to the underlying Weihrauch quality.
The trigger can be adjusted to a nice crisp let-off. Don’t just use it as it comes from the box. Read this whole report and don’t be afraid to experiment.
I don’t know if all RX-2 rifles will droop like this one did, but you’ll want to keep it in mind. If you get one that does, there are drooper mounts that will fix the situation.
Lastly, the RX-2 is primarily a hunting air rifle. Buy it in a large caliber (either .22 or .25) but don’t think that you’ll be able to plink all day. This is a rifle you can leave cocked and on safe as long as you hunt without worrying about the state of the mainspring — and that’s the biggest advantage of a gas spring.