Posts Tagged ‘Oehler 35P chronograph’
by B.B. Pelletier
I need to be humbled periodically to maintain my perspective on things. Fortunately, for me, I was created with many imperfections that make frequent humbling a certainty.
I was taking a .22 semiautomatic rifle apart several days ago to clean the action, and I got to the part where you remove the last drift pin and all the major and minor parts fly apart like a satellite that’s been hit by a particle beam. No chance to see where everything went because they all got disassociated at the same time.
When this happens, I have several mantras to address the situation. No. 1 is I imagine the item was assembled by a 19 year-old girl named Tiffany, while she is also talking to her coworkers, drinking a Slurpee and texting her best friend. Tiffany can put this thing together in 27 seconds and can spot (without thinking about it) when part 51b has been reversed in its slot, which is good because Tiffany isn’t really into thinking.
If that one fails and I still have parts lying all over the table, I think of Ishmael, who uses no special tools to assemble this item. He has a hole in one of the upright girders supporting the roof where he assembles these items all day long. It was blown through the steel girder 37 years ago with an acetylene torch, and it isn’t quite round; but time and use have polished the edges of the hole, and it’s the perfect assembly tool that was used by Ishmael’s father for the same purpose. With it, he can assemble a pallet-load of these things, whatever they are, before tea time.
When that one fails me, there’s only one thing left — the Machtar chant of assembly (see the movie Galaxy Quest). As it happens all too often, even this potent bit of magic refused to work, leaving me with a pile of parts that purportedly had once been a semiautomatic rifle. Had I not seen it in that condition, I would have doubted it.
I got the gun back together by scrutinizing each part and imagining the relationship it had with the other parts (see, mom, I can use that lump on my shoulders for something other than a hatrack!), but I hate it when that happens. Complex parts should self-assemble, like a wine glass filmed in reverse after shattering.
But this isn’t about me fixing a gun. It’s about me being humbled, so I’ll remember what it’s like to approach something new for the first time. Trepidation, you are my middle name!
So, when a Pyramyd Air customer asked for some pointers on the use of a chronograph the other day, I felt I had to spring into action. Here is his exact request:
I’ve read a good percentage of your BLOGs & articles (plus videos), but no-where do I see the distance specified to set-up a chrono for muzzle velocity for springer airguns, pistols & rifles. I use a ProTach Classic Chrono, with 36″ between “start” & “stop” sensors (originally for hand-loading). I’ve searched the net for an airgun industry std. (like for fire-arms), with no success. One article, on the net, said set the “stop” sensor @ 3 ft. from the muzzle ~ that’s impracticle!! How-about-it, B.B., Tom or Robert B.!! Rich
Where to place the start screen
Rich, if this was five years ago, I wouldn’t have a clue what to tell you. That’s because you’re coming from the world of firearms. I began using chronographs with airguns. Only very recently have I started using a chronograph for my firearms, and only recently have I learned the difficulties of figuring out where to place the start screen.
I typically place the start screen about one foot from the muzzle of the airgun. That’s almost ANY airgun, mind you, except for a big bore and one other exception I’ll mention in a moment. A couple months ago, while I was chronoing some centerfire handloads, I rediscovered why my Oehler 35P came with 15-foot cables. Even when the skyscreens are placed 10 feet from the muzzle, the muzzle blast from a .43 Spanish round will move them like a slinky in Shakeytown!
When it came time to test the Benjamin Rogue, I was prepared to move the skyscreens way downrange from the muzzle to keep from blowing them apart from the air blast. Even though the start screen was situated about 10 feet from the muzzle, the entire skyscreen assembly shook violently every time the rifle fired. So, I understand Rich’s question at the most visceral level.
Rich, a spring gun discharges only the tiniest fraction of pressurized air that a pneumatic puts out, so you can place the start screen a foot from muzzle of the most powerful spring rifle or pistol you can find, which would be a Whiscombe JW80 generating 32 foot-pounds in .25 caliber. Ain’t nothin’ badder than that out there (in spring guns, that is), and your chrono will never miss a beat!
CO2 guns — the other exception
CO2 guns, however, often have a visible exhaust that can fool the skyscreen. Whenever I chrono one of them, I back up about 18 inches from the start screen. This holds true for the weakest pistols as well as the more powerful rifles. You don’t get an incorrect number from them, at least not from my Shooting Chrony Alpha model. What you get is an error message that screen one, the start screen, was unable to detect the passage of the pellet accurately. Back up a few inches, and the problem is solved!
The rest of the smallbores
As far as the other smallbore air rifles and pistols are concerned, 12 inches is all the distance you need between the muzzle and the start screen. This holds true for a catapult gun throwing a 3-grain lead shot at 86 f.p.s. as well as an AirForce Condor belting out a .25-caliber 43.2-grain Eun Jin pellet at nearly 1,000 f.p.s.
Watch where you’re shooting!
A funny story that is directly related. Many years ago, I was running an M203 grenade launcher range for my company at Hohenfels training center, West Germany. The M203 is an underslung weapon that attaches to the bottom of the M16 rifle. It lobs a 40mm grenade out several hundred meters and has been called the hip-pocket artillery of the infantry.
Attached under the rifle, the M203 grenade launcher lobs 40mm grenades out to 350 meters. It uses special high-angle sights, which the firer must not forget to use!
Here’s the thing about the M203. It shoots only a few hundred yards, while the M16′s 5.56mm cartridge can shoot several miles. Naturally, the rifle shoots much flatter than the grenade launcher, so the grenade launcher comes with its own set of sights designed to elevate the weapon to a very high angle to get the needed range. If you were to use the rifle’s sights, the grenade would hit the ground just a few yards downrange — and that would be a bad thing.
This young man demonstrates the correct angle for the M203 grenade launcher.
The firing positions on the M203 range were simulated foxholes with bermed bunkers in front and on both sides of each shooter. These berms were made of railroad ties that held back mounds of compacted dirt. Each firing position was protected from the others so that if anything bad happened, only the one position would suffer the consequences. On this day, I found out why — to my chagrin.
Even though I briefed each relay of shooters before they went to the firing points about using the M203 quadrant sights and not the rifle sights, and even though each firing position had an NCO to watch the shooter, we had an incident where a shooter forgot and used his rifle’s sights to engage a target. The grenade came out of the launcher and hit the railroad ties that were about 12 inches in front of him.
No, he didn’t blow himself up. The designers of the M203 grenade anticipated this event (it’s fairly common) and made the grenade to be armed by spin. It has to travel a certain distance downrange before the centrifugal force of it spinning from the rifling arms it, and 12 inches isn’t far enough. After the range was called cold and evacuated, I went to inspect the firing position, where I found a crumpled grenade lying in the dirt, next to the abandoned weapon. Just from the sheer velocity of the projectile, the grenade had dented the railroad tie about two inches!
Bad things can happen
I won’t tell you how I fixed the situation, but my point is this — when the sights and the bore are not aligned at close range, bad things can happen. The same is true with chronographs! If you’re shooting into a pellet trap that’s three feet away and you sight through the scope, you’re going to shoot your chronograph because the bore is three inches below the scope. Don’t think you’re smarter than that, because everyone who uses chronographs shoots them sooner or later. By sighting through the scope, you’re almost guaranteed to put a pellet through the guts of the electronics package.
Instead, sight by instinct, looking at the orientation of the barrel relative to the target, and of course to the skyscreens. Do this both for the elevation above the skyscreens as well as for the line the pellet takes across both screens.
People sometimes place a chronograph downrange to calculate the terminal ballistics at a certain distance; or, if another chronograph is used near the muzzle, the ballistic coefficient of the projectile. But they forget that downrange the projectile can go wherever it wants. More chronographs have been ruined this way than any other. Figure that it is only a matter of time before the downrange chronograph is hit.
Lighting for a chronograph
The best light for skyscreens is an even light. A totally overcast day is perfect, as is a day with clear blue sky (as long as the sun does not shine directly on the skyscreens). But a day with puffy white clouds that move around is bad, and you’ll have to use the diffuser filters above the skyscreens.
For artificial light, incandescent bulbs that shine evenly are the best. Bulbs that shine by exciting either a gas or a phosphor, such as fluorescents, cannot be used. They will set off the skyscreens.
I personally have found that by reflecting a 500-watt incandescent light off a white ceiling, I get the optimum in indoor chronograph lighting.
Here’s a small lighting tip. Don’t use strobe flashes near the chronograph, because they will set off the skyscreens. So will the arc from an electric welding torch.
On the level
When you shoot through the skyscreens, it’s important to be as close as possible to perpendicular to the path of light to the screen. If you shoot on an angle — up or down doesn’t matter — the path through the screens will be longer than if perpendicular and the recorded velocity will be lower.
You’re in charge!
Most chronohraphs run on batteries. I should not need to say it, but always carry a spare for when the battery dies. It’s discouraging to be out on a range, only to have the battery die and not have a replacement — especially when the whole reason for going to the range was to use the chronograph.
A few chronographs use infrared sensors in their skyscreens and need infrared light sources in order to work. If you lose one of these special-purpose bulbs, all the bright lights in the world will not make up for it. Keep spares close by.
What about that neat little Combro chronograph that attaches to the muzzle of the gun? How good is it? Well, I once owned one and can comment. It does work and you do get a number from it. And whenever there’s a number, people stand around and believe it.
But here is the deal. Oehler, which is admittedly the leader in commercial chronograph technology, separates his skyscreens (the third one in the middle is the stop screen for a second channel that checks the other one) by at least 24 inches. The machine’s clock speed (the frequency at which the crystal oscillates) is four megahertz. While the pellet flies between the start screen and the stop screen, the oscillator is counting at the rate of four million cycles per second. At that rate, it can parse time into small packets. The Combro has screens that are only a couple inches apart and a clock speed they don’t publish, but which must be slower than the Oehler. The number you get from this device is at best a close approximation — a best guess.
Aside from that, the Combro uses IR sensors, will not operate well in strong daylight and is difficult to fit to the muzzle of the gun. If it’s misaligned when mounted, it can be hit by the projectile. It’s not suited to use with firearms.
I answered Rich’s question in one paragraph in this report, then I went on to discuss other common problems encountered when using a chronograph. If you have any other questions or would like to know more, please make a comment to that effect.
by B.B. Pelletier
Today, I’ll test the velocity of the Sam Yang Big Bore .50 caliber Dragon Claw single-shot air rifle. For this test, I used two Air Venturi bullets and a swaged round ball that are available from Pyramyd Air.
The rifle is supplied with a probe-type quick-disconnect fill device, and I can finally report that the Koreans have now conformed with the rest of the world in supplying these adapters with standard threads that attach to common 1/8″ BSP fittings. In the past it was a chore matching these adapters to hoses you might have on hand (if you’re already into PCP airguns).
The No. 1 recommendation I have if you’re buying the Dragon Claw as your first PCP is that you also purchase the Pyramyd Air Quick-Disconnect male fitting and switch out the fill port on your rifle. Then, you can fill from a variety of high-pressure air devices, including the Air Venturi 88 cu ft carbon fiber tank. You’re going to want something that large to keep this monster gun supplied with air.
Let me address the air issue right now. This rifle does use a lot of air. I found that I got four useable shots on high power or eight shots on low power, and each time I did that the gun dropped from 3,000 psi to 1,500 psi for high power and 1,200 psi for low power. This number of shots per fill is fairly good considering the caliber of the rifle, but you’re going to refill it often. Don’t even think of using a hand pump for this rifle!
Shot with open sights
I decided to shoot the velocity test shots with open sights to simplify things at the range, and in so doing I learned that this rifle shoots very low at 50 yards. So low, in fact, that it was impossible to move the point of impact up to the point of aim. That’s good to know, because I’ll want to use a scope mount with some droop correction for the accuracy test.
The rifle actually grouped pretty well with open sights, considering I was shooting three different projectiles at two different power levels for each. Of the approximately 25 shots I fired, about 21 grouped in a hand-sized group. Unfortunately, it was below the target paper, so I’ll leave all accuracy testing to Part 3. But this test did show me a couple things about the gun.
I know why there’s a low-power level
First, you may remember that I was skeptical about using the low-power level. Now I know why it’s useful. With the Air Venturi 200-grain round nose lead bullet, the rifle gave eight good shots on low power — and they all went into that group I mentioned. When I scope the rifle for the accuracy test, this is one power level I’ll definitely try.
On low power, the 200-grain bullet ranged from a low of 562 f.p.s. to a high of 613 f.p.s. The average was 598 f.p.s., which gives us a muzzle energy of 158.85 foot-pounds. That’s for eight shots on low power.
On high power, I got four good shots from all the bullets. The 200-grain bullets ranged from 687 f.p.s down to 610 f.p.s., with an average of 640 f.p.s. That’s an average muzzle energy of 181.95 foot-pounds. So, I got half the number of shots for a 23 foot-pound gain. It doesn’t seem worth it to me. They did group with the other 200-grain bullets, though.
The 225-grain Air Venturi round nose lead bullets also gave four good shots on high power. They ranged from 652 f.p.s. down to 581 f.p.s., with the average at 614 f.p.s. That’s an average muzzle energy of 188.4 foot-pounds. That’s not much better than the 200-grain bullets, so I think I’ll stick with the lighter bullets. These bullets also went into the main group with everything else.
On low power, the 225-grain bullets gave eight good shots, ranging from 614 f.p.s down to 521 f.p.s., with the average at 563 f.p.s. That’s an average muzzle energy of 158.4 foot-pounds. They also went into the main group at 50 yards.
It was the Hornady .495-inch round balls that didn’t do so well in this gun. They averaged just 465 f.p.s., so they must fit the bore very loosely. Since the balls weigh only 183 grains, the average energy was just 87.77 foot-pounds. They did not group with the other bullets. They were about six inches lower than the main group, though centered with it.
The Dragon Claw has a heavy trigger. I would estimate that it releases with about 8 lbs. of pull, and there’s considerable creep in the pull. The rifle recoils about like a lightweight .22 Magnum rifle or even a .38 Special fired from a rifle. A friend at the range noticed the recoil when I fired.
The gun cocks by pulling back on the spring-loaded hammer. It’s stiff in a new gun, and it takes a bit of finesse to stop on the low-power setting. The tendency is to haul back as hard as you can, which takes you right to high power.
Observations thus far
The Dragon Claw is a handy big bore that’s got plenty of power and is priced right for the category. It seems to be very good on low power, and I’m looking forward to shooting it with a scope.
Are there .17 caliber firearms?
J-F, one of our Canadian blog readers, asked this question and I thought I’d answer him here. Yes, there are plenty of .17 caliber firearms; though, just like the .22 calibers, they’re not the same size as airguns. In the case of .17 caliber, the firearm bullets are all smaller.
Two very popular .17 caliber firearms these days are the .17 HMR — that’s a .22 Winchester Magnum rimfire necked down to .17 caliber — and the .17 HM2, which is a .22 long rifle necked down. The HMR leads the HM2 in the popularity contest, even though the ammunition is three times more expensive.
I have a .17 HM2 rifle that a friend of mine built for me on a Hungarian single-shot .22 long rifle action. You’ve seen this rifle before, because it’s the same gun I used for testing the Blue Wonder cold bluing process. And, the blue is still beautiful on that barrel, despite my never wiping the gun down and purposely handling the barrel to see if I could get the finish to wear.
The .17 HM2 cartridges are based on the .22 long rifle round.
My .17 HM2 rifle is based on a Hungarian single-shot trainer. I blued the barrel with Blue Wonder cold blue in another report.
I cleaned the barrel just for this report, so naturally I had to shoot several rounds to foul the bore again. A clean barrel almost never shoots to the same point of aim as a slightly dirty one. Once I was satisfied that the rounds had stopped walking, I adjusted the sights and shot a five-shot group at 50 yards. It’s no great group, and several PCPs I’ve tested will beat it hands-down, but it’s in the right place.
Not great but also not terrible for open sights at 50 yards. The .17 HM2 is a nice, inexpensive varmint cartridge.
So, yes, there are .17 caliber firearms, as well as pellet guns. That’s my report for today. Next time, I’ll have a scope on the Dragon Claw, and we’ll see how well she can do.
by B.B. Pelletier
When I started The Airgun Letter back in March 1994, I did so out of frustration. I had just subscribed to American Airgunner magazine and they folded, leaving me with half a subscription unfulfilled and an unquenchable thirst for more information about airguns. I could buy all the gun magazines I wanted, because there were over a dozen titles on the newsstands back then, but there was never one about airguns. And, the few articles gun writers wrote about airguns were trash back then…just as it is today.
Edith suggested that I write my own magazine about airguns, and I thought she was crazy. I told her I didn’t know enough about them to fill a whole magazine, so she suggested that I write a monthly newsletter, instead. I still thought she was out of her cabeza, but at her suggestion I sat down one day and wrote the titles of all the articles I knew I could write about. When I had three-and-a-half legal sheets filled with one-line titles (about 150 titles) I figured it might be worth a try.
The rest of the story is that we started publishing the newsletter in March 1994 and added 50 percent more pages a year later because I needed the extra space. Then, we also published six different 100-page magazines called Airgun Revue, for which I wrote historical airgun articles.
The only reason we stopped publishing the newsletter was we were losing money. People were copying the newsletter and sending it to their friends. I had thousands of readers the world over, but most of them were not paying for a subscription. Plus, the internet was growing, and we also found some of our articles online. In those days, it was harder to shut down another website for infringing on your copyright.
But back to today’s report. One thing I did when I wrote my newsletter was address topics that no other writer would. There were deep dark secrets back in those days, and various interest groups didn’t want the great unwashed (that’s everyone except themselves) to know these things. So, I wrote about them in a column called “Balderdash.” Two of them have to do with today’s blog.
There were several myths about multi-pump pneumatics that were being espoused on the few chat forums we had back then. One was the myth that a multi-pump loses power when left to sit for a long time after pumping, because pumping generates heat (the heat of compression); and when the gun has the chance to cool off, it will slow down significantly.
Another myth was that the cadence at which you pump each stroke has a tremendous effect on the power output of the gun. I’m going to answer those myths right now.
I tested both questions, using my Sheridan Blue Streak and a Japanese-made Sharp Ace I owned and found that pumping the gun fast or slow had virtually no effect on velocity. There were differences, but they were smaller than the total variation of velocity both guns had, so the results were “in the noise,” as electronic engineers like to say. There was no difference in the velocities of the guns whether they were pumped slow or fast that could be supported with statistical confidence.
What about shooting immediately as opposed to waiting for a long time? Would velocity vary then? Many said that it would, because the heated reservoir (and the air inside) would have time to cool and therefore lose energy. W.H.B. Smith claimed in his classic book, Smith’s Standard Encyclopedia of Gas , Air and Spring Guns of the World, that there would be a difference from the loss of heat over time, but it would be very small. Back in 1995 when I ran this test, Smith’s book was one of the only books on the subject of air-gunnery in existence. We knew even then that there were errors in the book, such as the low results he got with the HW 54 EL Barakuda ether-injected rifle that was probably due to a blown piston seal. But since it was just about all there was, we read it and thought about it and this idea of power loss through cooling became a fact.
The test I ran with my Sharp Ace indicated a small difference in power that favored the hotter gun over the gun shot later, but the results were, once again, very close. At about 770 f.p.s., the two results were separated by just seven f.p.s. for 10 shots. I concluded that the difference might actually exist, but that it was too small to be of practical interest.
But let’s set those two questions aside now, because yesterday, blog reader Aaron prompted me to write this blog when he responded to my test of accuracy between the Ruger 10-22 and the AirForce Talon SS that wrote about in yesterday’s blog. Aaron said that he could not understand comparing airguns to powder burners. That each was created to do a different thing and that any comparison was therefore senseless (I’m using my own words to paraphrase his thoughts here).
I agree with Aaron that we shouldn’t compare airguns and firearms — except that so many people do. When I was growing up, I heard a lot of older boys and even men saying, “That old Benjamin of mine is as powerful as a .22. I just pump her up 30 times and she cracks like a rifle!”
Overlooking the fact that the gun they were talking about probably was a rifle, I understood what they meant and I’m sure you do, too. What they meant was their multi-pump, when pumped about 30 times, had (they assumed) all the velocity and (they assumed) power of a .22 rimfire cartridge.
At this point, blog reader twotalon chimed in to tell us he knew what the outcome of this test would be. Well, he was right, but there is a VERY important point that we all need to understand. While conducting the first test about the speed of the pump strokes affecting the velocity, the first time I ran the test I actually proved that it did! And I published the results that way!
Several people took exception to my findings, and at about the same time I was testing the Beeman R1 for the articles that would eventually become the R1 book. Well, I discovered that my ancient Shooting Chrony chronograph that I bought used from Paul Watts could be “tricked” into displaying velocities faster or slower, depending on the angle of the pellet path through the skyscreens. I had to throw out a lot of R1 test results after I found out how to “cheat” the machine by angling the barrel for the shot. And that made me wonder about everything else I had tested with the same machine, so Edith and I bit the bullet and I bought a new Oehler 35P chronograph.
The new chronograph showed that there was very little difference between slow and fast pumping, so I had to print a retraction to the earlier article. I also learned the value of good equipment, because I had to rerun a lot of the R1 tests that were already in the can.
I’m not saying anything bad about today’s Shooting Chrony chronographs. I use one most of the time these days. But the one I had been using for those tests was one of the very ancient ones that had cardboard “windows” above each skyscreen, and the ones on my machine had been so shot to pieces that the results were unreliable. You’d get a three-digit number, but how close it came to the truth was anyone’s guess.
Back to the report
At any rate, I’d always wondered if the old guys were kidding themselves by thinking an overpumped pneumatic was more powerful, so I conducted a test. I really didn’t want to pump my Blue Streak more than eight times because ever since it was brand new in 1978 I’d been so careful to limit my pumps to a maximum of eight, just like the manual advised.
I’m sure that I conducted that test and published the results somewhere, but I can’t find it anywhere in the index of the Airgun Letter. So, I had to run another test for you today. Once again, I drafted my 1978-vintage Blue Streak for the job. And we remember that the manual that I lost years ago, but which Pyramyd Air has in their online library of manuals, says that 8 pumps are the maximum. So, let’s roll!
For this test, I used my old Blue Streak, which I oiled especially for today. The pellets are all 14.3-grain .20-caliber Crosman Premiers.
Well, that chart shows what I was talking about, but not as well as I’d like. You can see the power drop off after the tenth pump stroke. But a Blue Streak should be doing that on pump number nine and the velocity should be much higher.
I could tell at pump five that my old Blue Streak wasn’t feeling well. It looks like the old gal finally needs some attention, because the last time I recorded the same pellet at 8 pumps it was going 643 f.p.s. and a few years before that it was close to 675. There’s reason No. 12 to own a chronograph.
Next, I pressed a Benjamin 392 into service. These days there isn’t much difference between the 392 and the Blue Streak, except for the caliber. My 392 is a pump-assist model that I reported on several years ago, but the powerplant is stock.
Same Crosman Premier 14.3-grain pellet was used, but this time in .22 caliber. Again, the gun was oiled before testing began.
That wasn’t the clear and obvious test result I was hoping for. In the past, I’ve seen velocities turn around after pump eight, or in some guns after pump nine and everything thereafter was slower. This time, the gun kept increasing until pump 13, where it went slower for the first time, but after that it seemed to want to remain at about the same velocity no matter how many pumps were put into the gun. This wasn’t from residual air pressure remaining in the reservoir, because I was dry-firing the rifle after each shot from seven pump strokes on. Usually, I’ll be able to hear when the gun hasn’t exhausted all its air because there will be a small crack from the dry-fire afterward, but that didn’t seem to be happening with either my Blue Streak or this 392. The Blue Streak just needs an overhaul but there could also be some dynamic about the pump-assist conversion I’m not familiar with, I guess.
But the main point I wanted to make today was that the gun doesn’t just keep on getting faster and faster with each additional pump stroke, and that was proven in both tests. So, the myth of 30 pump strokes turning it into a .22 rimfire is just that — a myth.
I’m not blaming Aaron for any of this. He only said he didn’t think we should compare airguns to firearms. He never mentioned any of these old stories, but that was enough to set me off on this strange quest to expose some old-wives’ tales about our airguns.
Now, I have yet another sick air rifle to care for. It seems that the cobbler’s children will have to go barefoot a while longer.