Diana 27 – Part 6

by B.B. Pelletier

Part 1
Part 2
Part 3
Part 4
Part 5

Boy, do I have some neat stuff to share with you today! Some of it is so neat that it’s prompting me to publish still another part to this test before tearing into the Diana 27 powerplant. Yes, I’m talking about a Part 7!

But let’s do Part 6 first. You may remember that last time I tested the rifle with a synthetic breech seal provided by Vince. I installed the seal and showed you a picture of it, then I recorded the velocities with the same pellets that were used in the new leather seal report (Part 3). Before that, I had replaced the old leather breech seal with one I constructed from an old belt.

You may also recall that several of you felt I had trimmed the new leather seal too close, and you felt it could not seal as well as it would have if it were left standing proud of the breech. You chastised me and instructed me to make the synthetic seal stand proud of the breech. Vince even provided the new o-ring that became the seal, as well as a thin steel washer for extra spacing.


Several readers felt the new leather seal should not have been trimmed this close to the breech. They thought it would have lower velocity than if it stood proud of the breech a few thousandths.

So, the synthetic seal was supposed to increase velocity over the new leather seal.


The new synthetic seal stood proud of the breech face just a little. Several readers felt this was not high enough.

I showed you the velocity of the rifle before (with new leather seal) and after (with synthetic seal standing slightly proud of the breech), and we all saw that the synthetic breech made the gun slower with two pellets (RWS Basics and RWS Superdomes), faster with one (Crosman Premiers) and was an improvement with Eley Wasps, but it wasn’t clear how much.

Several readers didn’t like the outcome of that test and scolded me for not raising the synthetic breech seal high enough. I was instructed to repeat the test with a higher breech seal. Today, we’ll see the results of that work.


When seen from the side, this is how high I originally installed the synthetic breech seal.


I cut a new plastic washer from a peanut tin top. This was installed behind the synthetic breech seal along with the steel washer that was already there.


This is what the synthetic breech seal looked like for this test.

Eley Wasp pellets
Eley Wasps hadn’t worked well with the new leather breech seal I made for the gun. They shot in two different velocity ranges–or so it seemed at the time. The low range was from 242 f.p.s. to 269 f.p.s., and the high range was from 588 to 620 f.p.s. At the time, I believed those low velocities, but I have since learned that a lighting condition on my test range gives artificially low velocities with certain pellets. I can repeat the low velocities at will, yet bring the rifle back to full velocity just by moving the muzzle back one foot, so I now know the low velocity range I reported then was only a lighting trick. The leather seal was actually shooting from 588 to 620 f.p.s.  all the time.

With the first test of the synthetic seal–the one that may have been too low– the average velocity jumped to 598 f.p.s., with a range from 588 to 612. In other words, not much different than with the new leather seal.

With today’s higher synthetic seal, the velocity with Wasps averaged 572 f.p.s.. That’s clearly a drop of 15-20 f.p.s. from either the new leather seal or the first (lower) synthetic seal.

RWS Basic pellets
RWS Basics gave an average of 658 f.p.s. with the new leather seal, and an average of 643 f.p.s. with the first synthetic seal.

With today’s higher synthetic seal, Basics averaged 634 f.p.s.–a definite drop in velocity from the last two tests.

Crosman Premier 7.9-grain pellets
Crosman Premier 7.9-gain pellets averaged 588 f.p.s. with the new leather seal. With the first synthetic seal, the average increased to 605 f.p.s. Today’s higher synthetic seal netted an average of 579 f.p.s, or a drop in velocity from both earlier tests.

RWS Superdome pellets
RWS Superdomes averaged 588 f.p.s. with the leather seal and 586 f.p.s. with the first synthetic seal. With today’s higher seal, they averaged 564 f.p.s.–a pronounced drop.

What about a higher leather seal?
You didn’t stop with wanting the synthetic seal to be higher. You also told me to raise the height of the leather seal to see if that had any affect on velocity. I removed the synthetic seal and replaced it with the leather seal that was used in the earlier tests in Part 3.

Both the steel washer and the new plastic washer were left in the seal groove, so the leather seal now stood very proud of the breech–for a while. After several breech closings, the leather squashed out in all directions and became visibly lower.


After closing the breech a few times the leather seal squashed out like this. Compare this to the height of  the first leather seal shown above and you will see that this one is higher. However, no matter how high you make the leather seal in the beginning, it will ultimately get smashed this low because the breech is tight. Leather cannot resist the smashing force of steel against steel, so it just squashes out until it fits the clearance perfectly.

Eley Wasps
Eley Wasps averaged 587 f.p.s. with the higher leather seal. That’s a small drop from the first leather seal and the first synthetic seal.

RWS Basic pellets
RWS Basics averaged 648 f.p.s. with the taller leather seal. That’s a drop from the new lower leather seal, but an increase from the first synthetic seal.

Crosman Premier 7.9-grain pellets
With Crosman 7.9-grain Premiers the average velocity with this taller leather seal was 592 f.p.s. That’s a slight gain in velocity over the lower leather seal and a decrease from the average with the first synthetic seal.

RWS Basic pellets
Basics averages 648 f.p.s. with the taller leather seal. That’s slower than the lower leather seal and faster than the low synthetic seal.

Crosman Premier 7.9-grain pellets
Premiers averaged 592 f.p.s. with the taller leather seal. That’s slightly faster than with the lower leather seal and slightly faster than with the first synthetic seal.

RWS Superdomes
Superdomes averaged 568 f.p.s. with the taller leather seal. That’s slower than both the lower leather seal and the first synthetic seal.

Before you jump me for not reporting how the taller leather seal relates to today’s test of the taller synthetic seal, allow me to mention that NONE OF IT MATTERS, BECAUSE THE ENTIRE TEST IS BIASED.

Oh, yes, dear readers, the entire test has been biased from the start, and I will tell you all about it in the unprecedented Part 7. Coming very soon! Boy, am I learning a lot about this particular rifle!

58 Responses to “Diana 27 – Part 6”

  • kevin Says:

    B.B.,

    The entire test is biased? All this velocity testing with various breech seals is out the window? Say it isn’t so. I envisioned this fascinating test of various breech seals of various heights to be cross referenced in your new library not only as critical info on the diana 27 but must read info about breech seals in older break barrel guns.

    My diana 27, with the original leather breech seal, is shooting superdomes at an average of 572 and cp 7.9′s at an average of 581 which is right in line with your velocity tests. I can’t imagine you opened up this gun and found a broken spring or canted spring or? since our guns are shooting so similarly.

    Now I’m very interested in part 7. This is a novel mystery.

    kevin

  • B.B. Pelletier Says:

    Kevin,

    Oddly enough, this time the news isn’t bad. Yes, the whole test is biased and therefore not accurate, except in a very general way, but when I tell you about the bias, it turns out to be in our favor.

    Don’t miss part 7!

    B.B.

  • kevin Says:

    B.B.,

    You’re a professional tease.

    A miniseries that guarantees I will tune in next week. Same bat time, same bat channel.

    kevin

  • kevin Says:

    B.B.,

    WHOA, wait a minute. My brain just woke up.

    Our chrony numbers aren’t the same. I shot my chrony numbers at 5,400 feet in elevation and you’re 712 feet in elevation. That means our velocity numbers are roughly 6%-7% apart.

    Now I’m really intrigued.

    kevin

  • B.B. Pelletier Says:

    Kevin,

    KAPOWIE!!!

    B.B.

  • kevin Says:

    B.B.,

    Just picked myself up off the floor. Uncle. I can’t stop laughing. Can’t even type, I give.

    kevin

  • Vince Says:

    BB, I suspect you’re gonna announce that I don’t know what the devil I’m talking about. Everyone will be surprised except me.

  • B.B. Pelletier Says:

    Vince,

    Not at all. This time the joke is on me!

    You come out as clean as a whistle.

    B.B.

  • David Says:

    Vince,
    I will back you up that I KNOW FOR A FACT that your shimming a breech seal actually works !!! I did it to my 34 Panther .22 cal and increased from 690 fps to 757 fps shooting 14.2 gr. Super H Points. Also did the trick on my Ruger Air Hawk and increased from 895 fps to 920 fps with 8.2 gr Meisters !!!

  • Anonymous Says:

    Herb,

    You keep some pretty strange hours! Regarding energy transfer from gas to pellet, I don’t think you can consider only the speed of the gas in isolation from the weight. Energy depends on both. So for the example of air and water, the air may flow faster, but the water will hit harder.

    I also think some distinctions need to be made. The speed of the mass of gas moving along as a whole is different from the speed of the molecules bouncing around inside of the gas. And the rate at which energy is transferred say from a gas to a moving projectile may be different from these. I would have thought that the transfer would be related to the pressure exerted but I do not know the relationship.

    No doubt there are many intricacies at the micro-level. But I still want to stick with the big picture of energy conservation which is that the energy required to compress a gas to a particular pressure will have to result in a projectile moving at the same speed regardless of the gas. If the argument is that this same speed of projectile is achieved at different times, sooner or later depending on how fast the gas is moving or transferring its energy, I am skeptical of that, but I guess the numbers would tell the tale for sure.

    Matt61

  • .22 multi-shot Says:

    Herb & Matt61,

    The one thing that could make it so that Helium creates a higher speed on the pellet is that it flows easier through the system (the molecules are smaller). That is what happens when converting from CO2 to air. Think of ping pong balls vs baseballs flowing through a giant valve and barrel. More ping pong balls can get through faster.

    .22 multi-shot

  • ChosenClay Says:

    I do not no if you saw this B.B.,
    so I’ll do it again.

    Hey guys!
    I discovered that the Crosman 2100
    looks like the Remington nylon 66!
    I read a article on the nylon 66 in
    American rifleman, and it had a
    picture of it, And low and behold,
    it looks like a 2100! is it perhaps a replica? wondering if you guys knew or not.
    Ian

  • Herb Says:

    Matt,

    RE: “… I would have thought that the transfer would be related to the pressure exerted but I do not know the relationship. …”

    Yes it is. The work done on the pellet is the pressure behind the pellet times the cross sectional area of the pellet times the distance over which the pressure is applied.

    Let’s divide barrel into N sections. We’ll average pressure over that section as the pellet passes.

    WORK(i) = P(i)*A*Barrel_Length)/N

    P = pressure in PSI (pounds per square inch)
    A = cross sectional area of pellet in inches squared
    Barrel_Length = measured in foot(s)

    Note that I didn’t measure barrel in feet because I wanted foot-pounds as the dimensional units. ;-)

    Total work done ON the pellet is to sum WORK(i) from 1 to N

    Imagine that instead of the valve on the PCP closing that it is just blown open and all the gas dumps out behind the pellet.

    Now just as the pellet exits the barrel, I have my Star Trek force fields separate each 1/N-th section of the barrel. Do all the sections, and the pressure reservoir, have exactly the same pressure?

    My educated guess is no. I would expect a higher pressure towards the breech. The difference in pressure along the barrel is because the gas molecules can only travel so fast. If the gas molecules could travel “infinitely” fast then the actual pressure in each section would be the exactly the same.

    Now the second part of the question is stickier. Are the differences in pressure significant? A millionth of a psi difference between the section at the breech and the section at the muzzle is enough to prove that gas molecules don’t travel infinitely fast. But such a small difference would be insignificant in the work done on the pellet.

    Does this make sense?

    Herb

  • ajvenom Says:

    Will the seals last as long when you shim them? Then again, seals are not that expensive.

    I’ve always noticed that most air rifles don’t always shoot at their advertised velocity. Perhaps shims could be the missing link for springers or a new tuning technique.

    I’ve given up on the 10M challenger sights and went back to a scope. I was shooting only 4 to 6mm c-t-c at 10M with the daisy 953 with some trigger modification. The 1 to 3mm I get using a leapers 4x32AO is so much more satisfying. I recommend JSB exact heavy pellets.

    I will leave the 10M and scope set up for the 953 so I can practice using both. Changing them is pretty quick using thumb knob screws. If they are set in the original places, the poi remains rather close.

  • B.B. Pelletier Says:

    Ian,

    Yes, I saw it. Did you see where one of the other readers posted a response to it on one of the other places where you posted it? He agrees with you.

    B.B.

  • Anonymous Says:

    BB off topic but,
    I would like to know if you know ANYTHING about the Norica youngs that are on sale at pyramid air, and if anyone else can answer this that would be awesome. It looks nice, in the price range I want and also has 9.5 lbs cocking effort (as specified on pyramidair.)
    Thanks
    DD

  • ajvenom Says:

    http://www.norica.es/index.php?opt=6

    I always thought beeman gh or gs modles were Gamo or gamo chinese copies?

    Reviews are always a good place to start.

    A few here, but not the same models:

    http://www.reviewcentre.com/fi9-brand-Norica.html

    BB how would you rank cometa, gamo and norica as a whole?

  • Anonymous Says:

    RE: BB’s teaser

    I suspect it has something to do with chrony results – read section on Eley Wasps carefully…

    … “but I have since learned that a lighting condition on my test range gives artificially low velocities with certain pellets. I can repeat the low velocities at will, yet bring the rifle back to full velocity just by moving the muzzle back one foot, so I now know the low velocity range I reported then was only a lighting trick.”

  • Vince Says:

    Ajvenom, the GS/GH guns made by Norica guns are NOT like Gamo’s at all, other than the fact that they are breakbarrels. The compression tube bore tends to be bigger (26mm), the triggers are completely different (one is much better, the other is much worse) and the pivot bolt and lockup are built differently.

    The Beeman SS and RS (and some others, I think) are Chinese clones of the Norica’s.

    Personally (a non BB opinion coming) I believe Cometa is the best, the good-triggered Norica is second, Gamo is third, and the Norica with the bad trigger is last. These comments apply to the earlier Gamo’s with all-steel barrel, cocking and lockup parts. I know little about the newer ones (Big Cat, Whisper, etc.)

  • Herb Says:

    RE: Discovery calculations

    Still trying to work on calculations for Discovery.

    Given that you start at some fill pressure X and shoot a string of N shots, what is the final fill pressure Y?

    Want real numbers for X, N and Y. I’d like to know how many PSI/shot the pressure drops. I know that it depends somewhat on the pressure itself, but averaged over a string ought to yield a decent number.

    If a few of you Discovery owners couple remember to check this and report it I’d appreciate it. In part several different measurements would allow calculation of a % error around PSI drop.

    Thanks,
    Herb

  • Vince Says:

    Ajvenom, overshimming a breech seal will damage it, especially if it starts catching on the transfer port. But proper shimming will compress it without overcompressing it, and it should provide a very decent service life.

    BB – to my eye it looks like your latest shim went a little overboard and that the seal is sticking out a bit too much. Are you sure the breech is closing all the way, and that it’s not catching on the transfer port? Sorry if I’m asking the obvious…

  • .22 multi-shot Says:

    DD,

    I was sure BB had tested this rifle, but when I searched, I couldn’t find it. Perhaps it was this quote from him that made the impression on me, “All I can tell you is that Norica is a good maker, and the price for this gun is very low.” The quote is from the Ruger Air Hawk Elite blog
    http://www.pyramydair.com/blog/2008/06/ruger-air-hawk-elite-part-3.html

    .22 multi-shot

  • Herb Says:

    RE: Norica Young

    0.22 multi-shot, not your imagination – see:

    http://www.pyramydair.com/blog/2008/06/ruger-air-hawk-elite-part-2.html

    Herb

  • .22 multi-shot Says:

    Thanks Herb!

    That was what I was looking for, but it wasn’t a test of the Norica after all.

    .22 multi-shot

  • Jon F. Says:

    Matt&Herb,
    Using helium or hydrogen offers a significant advantage by doubling or tripling the SPEED OF SOUND in your propulsion medium which has everything to do with the final velocity of the projectile.
    If you will go to "Wikipedia Light gas gun" there is a very clear and concise explanation of N.A.S.A.'s (yes, designed by real rocket scientists) light gas gun. There are pictures and graphics and a brief physics description which explains why they use hydrogen to achieve maximum velocities.
    On a side note, did you know that commercial power generation facilities fill the generator enclosure portion of their turbine generators with hydrogen gas? This reduces friction with the atmosphere in which the generator spins (windage losses)and increases generator and hence overall plant efficiency.
    When they are running you can look inside and see the field brushes arcing on the slip rings but there is no oxygen present therefor no fire or explosion.
    Jon F.

  • B.B. Pelletier Says:

    Vince,

    I think you are right. The higher seal is perhaps too high. The height of the leather seal is now where the original synthetic seal was, so that was probably the right height. The velocities seem to agree with that, as well.

    B.B.

  • B.B. Pelletier Says:

    ajvenom,

    If the seal is too high it can tear. Mine hasn’t, so there is no problem.

    B.B.

  • kevin Says:

    ajvenom/Vince/et al.,

    Re: Rank cometa, gamo & norica as a whole

    I think Vince summed it up nicely but I'll throw in my little bit of experience.

    I owned a gamo hunter and gamo whisper. Replaced the trigger on the gamo whisper (I think, maybe the hunter) with a grt. Vast improvement. The gamos were never tuned. Jumpy, twangy and very hold sensitive. Sold both of them. The only gamo I would ever consider owning again would be a cfx if it was tuned and included the grt trigger and then it would have to be a door prize in order for me to take it home. I've only owned one norica. A norica krono which was rebadged as a beeman gs700 and also known as a marksman 0035. The norica krono is undoubtedly one of the "norica's with a bad trigger" that Vince referred to in his response that ended up last on his list. My norica krono had about 500 shots on it before the velocity fell off about 40%. I took this gun apart and found the spring canted in two places. This norica is one of the many models that has the pressed trigger unit that can't be improved. Many people have remanufactured a trigger unit for this gun since not much else can be done to improve it. The norica krono is the worst gun I've ever owned. I've never owned a cometa.

    kevin

  • BG_Farmer Says:

    BB,
    I’m hoping the surprise might be that chronographs aren’t that terribly accurate anyway, and that its a waste of one’s precious time on earth to mess with them if the rifle is shooting well:).

  • Anonymous Says:

    BB,
    I lifted the breach seal way up on my Storm Xt and it stopped leaking (baby powder test:) Does seating a tight pellet increase velocity? I usually seat pellets that stick out a bit.
    Shadow express dude

  • B.B. Pelletier Says:

    BG_Farmer,

    Yes, and Allis-Chalmers tractors can be accidentally started when a wren alights on the hand-crank!

    B.B.

  • B.B. Pelletier Says:

    SED,

    Seating pellets is a fine line, but I find that once they are in past their skirt, the velocity drops. They seem to like that “pop” they get from resisting until being overcome.

    B.B.

  • ajvenom Says:

    Thanks Vince, Kevin and BB.

    There we go..are cometa’s going to be on the Pyramyd list soon and how are those gamo poly bull/fluted covered barrels? Do they hold up? Do they loose any tolerances (ie, pivot point etc..)?

    I like the old steel only barrels.

    I wouldn’t mind a cfx royal or 890 with a gas ram in a .22 hitting 800 fps with lead.

    If it was a door prize, then fit me up with a more deluxe model. Then again a Marauder would be nice too.

  • Anonymous Says:

    Herb,

    I think you’re right that in the absence of a projectile, the speed of gases down a barrel differs depending on the type of gas because lighter molecules will go faster, but I don’t see that this correlates exactly with how fast the same gas will push a projectile. Modeling the individual gas molecules with classical mechanics, the energy of each is .5mv^2. The sum of the energies of all the particles is what is ultimately producing the speed of the projectile. Put in a certain amount of energy to compress the gas, and the same should come out in the kinetic energy of the projectile. The lighter weight of the molecules should offset the higher speed to conserve energy. That’s how I’m understanding this process.

    Now enter Jon F.’s very interesting Wikipedia reference. Indeed, NASA does appear to use gas guns with hydrogen and helium to produce phenomenal velocities, and there is language about the speed of sound and pressure differentials as factors in airgun speed. However, there are a couple problems. In its explanation, the article claims that the speed that a projectile can be pushed is limited by the speed of sound of the medium. Well, that is demonstrably not true since spring guns using air can go supersonic. So something is seriously wrong with the physics here. The second, related point, is (enter the librarian) nobody knows who is writing these Wikipedia articles. Haw haw. While generally they tend to be surprisingly accurate, no one can vouch for every bit of information at any one time.

    The use of hydrogen and helium is suggestive, and perhaps they have something to do with higher projectile speeds although not in exactly the same way that the article describes. I’ll leave these questions to Jane or somebody else.

    Meanwhile, have we shown that these questions are of limited relevance to commercial airguns? B.B. himself brought up the example of the NASA super airgun many blogs ago to illustrate that pure speed does not accomplish anything. To make up for the degraded accuracy at the supersonic level, you would need to modify the projectile and then you would just be reduplicating firearms. Moreover, I don’t know that any benefits of helium or hydrogen would apply to the practical barrel lengths of longarms which seem to max out at 26 inches. No one would carry a rifle of the length of the NASA airgun in the Wikipedia article.

    By the way, Jon F. I did not know that fact about turbine generators, but I wonder if the benefit of helium/hydrogen in the NASA airgun has more to do with barrel erosion as they article mentions.

    Matt61

  • Anonymous Says:

    Does anyone know if it’s harder to compress helium/hydrogen than air? I had been assuming that all gases take the same amount of energy to compress. If that is not true, then I could see these gases transmitting more energy and moving projectiles faster but not because of their speed of sound properties–although perhaps those are not unrelated.

    Matt61

  • Jane Hansen Says:

    Jon F. (& Herb)

    I just love this stuff…

    Light-gas guns may have been designed by rocket scientists, but they sure did not write the Wikipedia entry..

    Let's look:

    "The limiting factor on the speed of an airgun, firearm, or light gas gun is the speed of sound in the working fluid"

    So, how does a light-gas gun hit velocities of some 25,000fps, if the speed of sound in the working medium is only about 4000fps..?

    "the heat formed by the compression of the working fluid serves to increase the maximum possible speed" PCPs release air compressed air at ambient temperature, which COOLS the gas, yet they STILL exceed the speed of sound of their working fluid.

    Light gasses are better for all the reasons NASA and Herb like them – the molecules are smaller, will flow through orifices faster, and, being lighter, can accelerate faster. The faster these particles can accelerate, the less pressure drops as the projectile moves from breech to muzzle…etc..faster muzzle velocity.

    I don't see why someone can't try this just for fun and see what we get..

    Jane

  • Herb Says:

    RE: Hydrogen in PCP

    Under ** NO ** circumstances should hydrogen be put into a PCP. When the gun blows up I will not sympathize. I will not come visit you in ICU. I will not donate money for skin graphs.

    Oxygen from the atmosphere gets into everything. Also since you’re shooting into air the hydrogen will mix with the oxygen from the atmosphere.

    Using helium would not be a safety problem. Using hydrogen is just an incredibly stupid risk.

    Herb, the chemist

  • kevin Says:

    Herb,

    Now how do I get the hydrogen out of my gun?

    Jane, Matt 61, BG Farmer, etc.,

    I just want to know when this gun gets built that you’re in the infancy stages of designing, will it be hold sensitive?

    kevin

  • Herb Says:

    Matt,

    RE: “Does anyone know if it’s harder to compress helium/hydrogen than air? I had been assuming that all gases take the same amount of energy to compress. If that is not true…”

    For practical considerations the answer is yes, it takes them same amount of energy to compress them.

    In chemistry we always refer to the “ideal” gas. None of them are in fact ideal. The higher the pressure, and/or the higher the temperature, the more screwy things get.

    ———

    RE: “but I don’t see that this correlates exactly with how fast the same gas will push a projectile. Modeling the individual gas molecules with classical mechanics, the energy of each is .5mv^2. The sum of the energies of all the particles is what is ultimately producing the speed of the projectile. Put in a certain amount of energy to compress the gas, and the same should come out in the kinetic energy of the projectile. The lighter weight of the molecules should offset the higher speed to conserve energy. That’s how I’m understanding this process.”

    We’re mixing apples and oranges here.

    Consider this. The compressed gas has kinetic energy stored in the motion of the gas molecules. It also has potential energy stored as the pressure of the gas. When you release the pressure the potential energy (stored as pressure) can be converted into kinetic energy of the gas molecules themselves. This creates a flow of gas molecules down the barrel.

    1 cubic inch of helium or air compressed to 2000 psi has the same amount of potential energy stored.

    Assuming that all the gas molecules have the same velocity, and are directed down the barrel with a perfect orientation. Then you can in fact calculate how fast the flow of molecules is traveling based on the loss of potential energy.

    I just did the calculation for air and got 7800 fps for air at 2000 psi. More pressure, more FPS. Actually in this case since air is nitrogen/oxygen the kinetic energy of nitrogen and oxygen atoms isn’t the same. I wanted to split the energy so that the molecules have the same velocity so they don’t bump into each other reducing the flow rate. So oxygen molecules have more KE than nitrogen molecules.

    Helium atoms weigh less than air “molecules,” (average velocity as noted above) so helium atoms would travel faster.

    1/2 m(air)* V(air)^2 = 1/2 m(He) * V(He)^2

    assume air m = 29, he =4

    V(He) = v(air)* SQRT(M(air)/M(he))

    V(He) = 2.69 * V(air)

    Does this help?

    Herb

  • Herb Says:

    Jane,

    RE: “So, how does a light-gas gun hit velocities of some 25,000fps, if the speed of sound in the working medium is only about 4000fps..?”

    I know the question was rhetorical, but you raise the temperature of the gas. As you noted the speed of sound is not a constant. The hotter the gas, the faster the speed of sound in that gas at that temperature.

    Herb

  • Anonymous Says:

    If one was to fill two balloons(sp) , one with 1 mol of oxygen be the other with 1 mol H2 and held a match to them, which would generate more energy. Maybe rephrased which is more combustable(sp?) O2 or H2?

  • Herb Says:

    RE: which is more combustible(sp?) O2 or H2?

    Combustible by definition is "burning" by combination which oxygen. "Burning" implies that the oxidized compounds have lower energy. That is that the overall reaction releases heat.

    H2 – combines with O2 to produce H2O.

    O2 can't "burn" itself.

    3 O2 -> 2 O3

    or three molecules of oxygen can combine to produce two molecules of oxygen. But ozone is in a higher energy state than oxygen. hence it isn't "burning."

    Herb

  • Anonymous Says:

    Jane,Herb,Matt61 etal.
    I think you are all just blowing hot air!(but aint it fun?)
    BGFarmer
    Boy don’t I wish you were right (especially since I don’t have a chrony:yet)But I’m afraid it’s an essential tool,if for nothing but diagnosing potential problems.Just another wishlist item for my toy collection.Darn thing just keeps growin:)

    JTinAL

  • ajvenom Says:

    So if we hypothetically inhale the gas and use the one that makes our voice the highest, then that would be the winner?

  • ajvenom Says:

    oh no, now I’ve gone crosseyed….

    Suppose an airgun weighs less than a duck, would we still burn it?

  • ajvenom Says:

    oh no it posted…

    The riddle was suppose to be if an airgun weighs as much as a duck, would be still burn it?

  • Jane Hansen Says:

    OK, now that Herb is using more basic particle-motion physics, and getting more realistic expectations of attainable speeds, let’s see if we can convert the remaining “speed of sound” theorists.

    Sound travels through any medium by a continuous chain of “bumps”. The molecules, (think marbles), at one end of a tube sense a vibration, (a tap, push,what-have-you), and move in response, till it bumps the marble next to it, and so-on down the tube. It’s like a row of falling dominos, each one knocking the next over. The speed of the “wave” depends on many things – particle mass, proximity, temperature, etc., (and in reality, this is not actually a series of perfect, elastic, collisions).

    In the previous century, many thought that this speed of propagation was the limiting speed of anything propelled by the medium.

    Our view is somewhat different – Just imagine whacking the whole pile of marbles with a golf club, and off they go – as fast as you can hit them, or, just picking up the lead domino and throwing it. There may be some bumping and some sound waves propagating, but the whole pack of marbles is on the move, and they can move a whole lot faster than if they play the “tag” game.

    The speed of those marbles is not limited by anything, (within Newtonian physics), except the normal forces of drag, (friction, collisions, etc.) that slow down any moving object. Speeds of 25,000fps, 30,000fps, etc, have been demonstrated and are calculable, at any temperature.

    Lighter gasses do work better because of the same basic laws of motion. How much better is only a guess.. Because attempts to calculate speeds based on conservation of energy show us relatively quickly that current guns are not all efficient. Only a small percentage of the energy put into these guns, (by pumping, compressing spring, etc.,) ever gets turned into kinetic energy of the projectile. There are losses everywhere, (the valves, angles, ports, surface finishes, even the “tag” games being played), all sap energy….

    Some one needs to try some helium..

  • Randy-in-VA Says:

    Herb, Jane, et al

    I’ve reading along for the past episodes of “Have Gun, Will Travel (But How Fast?)”. I’m just a simple dirt and water engineer, but I think that the discussion has gotten way too complicated.

    1 – The flight of the pellet is best explained by Newton’s Second Law. Force equals mass times acceleration. The acceleration of a given pellet is determined simply by the force applied to it.

    The gun starts out as a simple piston. Force equals pressure times area. As the pellet moves, gas laws explain the decrease in pressure as the volume of the cylinder increases. This changes the force applied to the pellet.

    All of this neglects the effects of air resistance and friction in the barrel. Integrating all of this down the length of the barrel is best left to much smarter minds than me.

    2 – A smaller gas molecule has more energy because velocity is squared in the equation. The energy of the molecules is a red herring, however, because the molecules are going in every direction, cancelling their momentum.

    Ideally, it shouldn’t make much difference which gas is used. Practically, one may have better efficiencies than the others. That is where the helium experiment is required.

    3 – Would the velocity from a hydrogen detonation be admissable for the pellet speed record? (Assuming that the Chrony and/or shooter were still around to attest to it.)

  • DB Says:

    AJ,
    Still funny.

    DB

  • Herb Says:

    Randy-in-VA

    RE: 3 – Would the velocity from a hydrogen detonation be admissible for the pellet speed record?

    !@#$%^&*( BB is a spoil sport. He says no detonations for speed records.

    RE: "2 – A smaller gas molecule has more energy because velocity is squared in the equation. The energy of the molecules is a red herring, however, because the molecules are going in every direction, canceling their momentum."

    No. For an "ideal gas" the molecules have "infinitely large" velocities and your statement would be true. Furthermore for an Ideal gas there would not be any "dynamic pressure." The pressure would be entirely static. The pressure on the back of the pellet would be the same as the pressure on any part of the barrel. This also requires that the gas would not rarefy, so it has the same density in any part of the barrel. (If I have this part wrong I'm hoping Jane will correct me…)

    The problem is there isn't an "Ideal gas" and molecules don't have "infinite velocities." Hence the discussions.

    Even with an "ideal" gas there would have to be be a mass flow down the barrel. The gas has to have a net flow fast enough to keep up with the pellet.

    RE: "1 – The flight of the pellet is best explained by Newton's Second Law. … Integrating all of this down the length of the barrel …"

    Absolutely. But we are trying to figure out the force at each point in the pellets travel down the barrel. Imagine that we have a Discovery charged to 2000 PSI and a 16 grain pellet loaded. When we shoot the rifle the valve stays open and just dumps the gas down barrel infinitely quickly. Now from the starting pressure, the dead volume of the vale, and the increase in volume as the pellet travels down the barrel we could easily calculate the pellet's final velocity with some simple calculus. Unfortunately none of the critical assumptions hold. The valve does close. The gas doesn't move down barrel infinitely quickly. There are choke points in the gas flow. There is friction between the barrel and the pellet and so on and so on.

    Herb

  • Randy-in-VA Says:

    Herb,

    I don’t doubt anything that you are saying, I was just trying to express the problem in terms that were solvable. It seems that you are working on one heck of an equation. My last Calculus class was over thirty years ago, but I would recommend working out the simple model and then refining it to relate to the observed velocities.

  • Anonymous Says:

    Herb,

    Whether you evaluate the energy of compressed gas as potential or kinetic, it is a finite amount that should exactly equal the amount put in by the compression process and that should equal the kinetic energy of the pellet out the barrel.

    I’ll say again that I do not think that the speed of a gas in isolation mean anything. The only way the pellet knows to move forward is by collisions against its back from the gas molecules all of which are described in terms of energy transferred.

    And as Jane was saying (I think), I don’t know that the behavior of gas pushing a pellet can be described as a propagation of a sound wave based on a pressure differential. The pellet has to deal with friction down the length of the barrel and is additionally held in the chamber by some force. And I don’t know that the release of a compressed gas is really the same as a wave propagating along.

    Matt61

  • Herb Says:

    Randy-in-VA

    RE: “Solvable”

    Understand, but I’m a science geek. I’m more interested in the science than trying to create an empirical working model for an airgun. What fascinated me is the notion that there might be an absolute limit to how fast a “pop gun” can shoot a projectile.

    ————
    Matt:

    RE: “Whether you evaluate the energy of compressed gas as potential or kinetic, it is a finite amount that should exactly equal the amount put in by the compression process and that should equal the kinetic energy of the pellet out the barrel.”

    No – The output energy cannot, under any circumstances, EXCEED the input energy. It is likely to be much less because of the losses caused by friction gas flow and so on.

    So the output is not equal to input.

    RE: I’ll say again that I do not think that the speed of a gas in isolation mean anything.

    Disagree. Gas only travels so fast down a barrel. If the gas behaves “ideally” then P*V is a constant and the gas has the same density in every bit of volume as it pushes the pellet down the barrel. If the gas is not “ideal” (and no gas is ideal…) then the question is exactly “Is the gas density exactly the same in very bit of volume as the gas pushes down the barrel.” It really isn’t a question of “if” the densities are different, it is really a question of “how much” different.

    There is absolutely no doubt in my mind that there is some density difference between the breech end of the barrel and the muzzle end of the barrel in a fast PCP. The question here is basically is it ok to assume that the gas is ideal?

    Note: As gas expands volume goes up. Since the valve dumps a fix amount of gas into barrel, the absolute gas pressure will go down. But at any given instant, is the gas density the same throughout the volume?

    RE:The only way the pellet knows to move forward is by collisions against its back from the gas molecules all of which are described in terms of energy transferred.

    Agreed

    RE: “And as Jane was saying (I think), I don’t know that the behavior of gas pushing a pellet can be described as a propagation of a sound wave based on a pressure differential.”

    Not really trying to model a “real” rifle, as trying to understand the limits of how fast the gas itself can travel down the barrel. Once the upper limit is understood, then you add terms for friction and so on to account for various losses. Hope the notion makes sense.

    RE: The pellet has to deal with friction down the length of the barrel and is additionally held in the chamber by some force.

    Absolutely. These are all energy LOSSES that would have to be considered.

    RE: “And I don’t know that the release of a compressed gas is really the same as a wave propagating along.”

    This the really the question which we are trying to discuss. If the gas behaves “ideally” then we can keep making pellet go faster and faster by just using a higher fill pressure. If the gas isn’t ideal and we are reaching the limits as to how fast the gas itself can propagate down the barrel, then increasing the pressure won’t help much.

    So basically we start out at some pressure X and get a velocity Y. 2*X is not 2*Y but 1.5*Y, 4*X is not 4*Y but 1.8*Y, 500X is not 500Y but 2.9*Y. 1,000,00*X is not 1,000,000*Y but 2.99*Y.

    The numbers above are not meant to be real, but just point out what happens when you get to a point of diminishing return against an absolute limit.

    Herb

    PS – verification word is “PROVE” ?!?

  • Herb Says:

    BB,

    If you do another part on this gun, I’d be curious about a slightly different notion.

    I noted that with my Crosman G1 that its shoots 4 inches higher over 10 meters if I supported the barrel at the tip so that the weight of the rifle is pinching the breech closed.

    You should be able to measure distance between barrel and breach with automotive feeler gauges. Without seal at all, and with seal. Might give you some quantitative measurement on how thick seal needs to be.

    Herb

  • Anonymous Says:

    Herb,Jane,Matt61 et..al
    I wish you guys speak english like BB,Vince…so we simple gun nuts can enjoy the blog more. Thanks,
    Hank

  • Herb Says:

    RE: Pinching breech

    What i was trying to ask was foe chrony numbers with the breech “pinched.” If the breech is pinched, hen I would think that it would be sealed better.

    Herb

  • Anonymous Says:

    were is the breech seal on the oldest diana 27 air rifle

  • B.B. Pelletier Says:

    Where is the breech seal on the earliest Diana model 27. Is that what you are asking? Why? Do you have a 1910 Diana 27?

    If you do, break the barrel open and look. If the breech seal is not on the breech face, it is probably around the transfer port.

    B.B.

Leave a Reply


+ 3 = 4

Top-notch springer
Air Arms TX200 air rifle

When it comes to spring-piston air rifles, the Air Arms TX200 Mk III is a favorite of many airgunners, including airgun writer Tom Gaylord. His favorite caliber is .177. While the gun will initially impress you with its beauty and superior craftsmanship, you'll be even more impressed with the incredible accuracy! Tom claims this is "the most accurate spring gun below $3,000." Beech or walnut, left-hand or right-hand stock. Isn't it time you got yours?

All the fun, none of the hassles!
Uzi CO2 BB submachine gun

You've seen tons of movies with guys spraying bullets from their Uzi submachine guns and probably thought it would be a blast. Except for the cost of ammo! You can have all that fun with this Uzi BB submachine gun at just pennies a round. Throw shots downrange for hours on end with all the fun, none of the firearm hassles and a fraction of the cost.

Archives