Whiscombe rifles and barrel harmonics – Part 5More accuracy questions, plus a look at airgun power

by B.B. Pelletier

Part 1
Part 2
Part 3
Part 4

Well, the next big question everyone wants answered is this: Does high velocity put an end to all hopes for accuracy? Before I give you even more data to support the fact that it does, let me first clear up some confusion. I get comments from readers telling me that their .22/250 centerfire rifle that shoots 50-grain .22 caliber bullets at 3900 f.p.s. can group five shots in a half-inch at 100 yards. How can that not be considered accurate?

It is accurate, of course. But, the people asking the question were not aware that I was talking about diabolo pellets when I made that statement. Streamlined spitzer bullets handle hypersonic flight very well. Diabolo pellets do not. In fact, diabolos are made in such a way that they are not intended to be accurate above the speed of sound, or even in the transsonic region that exists above Mach 0.8.

Do we need better pellets?
This is where the newer airgunners often say, “Well, if diabolos aren’t accurate at supersonic speeds, let’s shoot solid bullets” without realizing that they are undermining all the potential accuracy an airgun has.

Airguns were never intended for hypersonic speeds. In fact, with the exception of a few extraordinary airguns owned by the government and used for test purposes (don’t lust after them, the barrels are 100 feet long in some cases!), only recently have airguns been able to achieve supersonic velocities. And, will all those who claim the speed of an airgun is limited by the speed of sound and who seek to “prove” it to me by directing me to this website or that chat forum PLEASE refrain from responding to this? I don’t mean to challenge you, but there are technical means of increasing the speed of airguns beyond what physical laws would seem to permit by changing their environment and thus changing the laws that apply.

I digress. The fact is, as a pellet approaches the transsonic region, a sonic pressure wave forms around the nose of the pellet. This wave generates turbulence that impacts on the skirt of the pellet, causing the pellet to vibrate and flutter as it flies. This causes increasing destabilization, the farther the pellet travels. At 10 yards you might not notice it much, but at 50 yards, it’s pretty obvious.

And here’s the proof
Immediately after shooting several tight groups like the ones I showed you yesterday and the day before, I removed the transfer port limiter to boost power. This was to test the Crosman Premier hollowpoint, but I also shot the Beeman Kodiaks at this power level. They went 929 f.p.s., which translates to 20.32 foot-pounds of energy. And they grouped poorly.


Boosting the velocity of Beeman Kodiaks from 813 f.p.s. to 929 f.p.s. resulted in this 1.589″ group – about one inch larger than it was at the slower speed! It is representative of what was possible at this power level.

Please understand that the HOTS was not tuned for this velocity, so I can’t say that the groups I got were the best you can get from this rifle and this pellet. But they were shot through the same barrel and by the same powerplant, and the same shooter on the same day at the same distance. So, the transsonic region is to be avoided, as well, if ultimate accuracy is your goal.

What is the transsonic region?
Read this two-part post. Then, read this post about the transsonic region. Those two postings should clear up the meaning of transsonic.

Another lesson – powerplant potential
The final lesson we’ll get from this session is the first step in learning about powerplant potential. The Whiscombe is set up as a .177 for these tests. So, the final thing I did was shoot several pellets to determine the maximum power potential of the powerplant for this caliber. You have read many times that light pellets generate more power than heavy pellets in spring-piston guns, and the reverse in CO2 and pneumatic guns. I fired several pellets to see what kind of power I’d get with the Whiscombe running wide open. The 7.9-grain Crosman Premier hollowpoints gave an average energy of 21.54 foot-pounds. Unfortunately, they were not very accurate at that power level. They really preferred to run at 14.63 foot-pounds.

Beeman Kodiaks were very accurate at 15.56 foot-pounds, but not nearly as accurate at their maximum of 20.32 foot-pounds. The old standby RWS Hobbys screamed out the muzzle at 1159 f.p.s. wide open and generated 23.57 foot-pounds. I didn’t bother to test them for accuracy because I know they cannot be driven that fast without scattering. Hobbys want to pull 10 foot-pounds and less in a springer. Only the gentler PCP or CO2 powerplants can drive them faster with accuracy.

Just to keep the heat on Gamo, I did test their Raptors. They scooted out the hole at the front at 1390 f.p.s., for 21.46 foot-pounds. Once again they did not live up to the promise of greater power than lead pellets and I know they can’t be accurate at that speed, either. Interestingly, they didn’t come close in velocity to the AirForce Condor, which punched them to 1486 f.p.s. I’m still waiting for someone with a 1600 f.p.s. Hunter Extreme to step forward.

What have we learned?
Well, I hope you now see a relationship between a pellet’s velocity and accuracy. If you do, you’re well on your way to shooting better. I hope you also see that the claims made by airgun manufacturers and carried forward by airgun stores are meaningless without accuracy figures to go with them. Sure, it’s neat to say a certain airgun gets 1000 f.p.s., but without any real accuracy, such a number is pretty worthless. Give me a rifle that shoots “only” 750 f.p.s. but can also nail its target every time. Close only counts in horseshoes and hand grenades.

38 thoughts on “Whiscombe rifles and barrel harmonics – Part 5More accuracy questions, plus a look at airgun power


  1. I tried that trigger adjustment but it just loosened the action. Is there any way to make the trigger better. It is supposed to be two stage but it’s more like a pull the toilet seat flusher. I am willing to polish sears and whatnot.

    Also, what should I do for my izh 46 before shooting it for the first time. I know that russian guns are usually packed in heavy grease.

    hb


  2. Hey B.B.,

    This series of articles has been very apropo. My “bro” in CA and I are about to send our Benjamin 392s to MAC1 for a steroid build, and our discussions of this have been fun, especially since a lot of what has come out of your blog the last couple of days has gone into our conversations. Pretty fun stuff to talk about when deciding on whether or not to tune (or steriod) an airgun.

    Anyway, not so much to stroke your ego, but I do appreciate your knowledge and authority on the subject of airguns. Do you think you could write up a detailed article about peep sites and how to use them? I just bought one for my 392, and they are indeed very accurate; I was quite impressed. But, I found that I couldn’t find much on the web about how to use them, which leaves me to believe that peep sites are a bit underrated in lieu of scopes. But I think they’re a great cost-effective alternative, especially at around the 25 yard range.

    Cheers,
    Steve
    Seattle, WA









  3. “Gamo trigger ”
    You can tighten the trigger adjustment screw , but you will still have a one stage trigger that is
    heavy and long.You can get a longer adjustment screw (I think 6mm) but from what
    I have read it won’t be safe and it will still be heavy.
    I’m going to get a trigger insert that is adjustable and light for about $8-$10 or
    for about $30 you can get a replacement trigger.
    Go here , then to the gamo forum ,and look for microgtx trigger insert.
    http://www.airguninfo.com/forum.shtml



  4. Mendoza,

    I haven’t tested Mendozas yet. We have mixed reports from our readers, the same as with most Chinese and Spanish air rifles.

    I can tell you that the Mendoza plant is undergoing a quality improvement program and that quality of the guns should be higher than ever.

    Maybe some owners will give you their assessments.

    B.B.


  5. I just got an email from JW. He said about $3000 for a JW 80 (1 .22 barrel) and an 18 month wait. I can live with that! It is good to know he is still at work. Ed Oldtimer



  6. Ya having a powerfull airgun is cool and all, but I get sick of the same crap, people trying to make an air rifle super powerfull.

    Seriously, unless you’re buying a .50 cal dragon slayer, or having a tuneup from places like big bore bobs(which sells 650 grain lead slugs for serious airgun hunters). Or unless you wanna spend 300 on a speacial purpose airgun.

    Airguns really weren’t intended to be FIREARMS AND THEY AREN’T!!! THEY ARE AIRGUNS, A DIFFERENT TYPE OF GUN!

    I mean ya there are some some serious air rifles the can be used for large game but those are special purpose guns and aren’t like your typical airgun.

    So if you really just care about raw power, plan on spending alot of money. Or njust go by a friggen firearm if your obsession is power.

    Thankfully B.B. you aren’t contaminated with airgun bias like most of blogs are, and I appreciate your honesty.



  7. I mentioned to you that JW told me that he would build me a JW80 for about $3000, 18 months build time. In a subsequent email to John he said he no longer builds .25 and that the real tack drivers are .177 at 1000 fps. I don’t like .177…traumatic experience when I was a child, maybe, but it seems to go against the whole trans sonic/super sonic balistic upset! estable@hotmail.com





  8. .177 caliber definately is not more accurate then .22, if anything .22 can be more accurate under certain cercumstances. Just because all competition guns are in .177 doesn’t mean anything, thats only because .22 is more expensive and .22 is intended more for hunting and longer range.

    I have been an avid airgun shooter for years and have not found .177 caliber to be more accurate than .22

    I personally like .22 alot better so maybe thats part of the reson I think .22 can actually be more accurate. Because as you mentioned B.B. pellets lose their purpose at super sonic speed

    and since making the caliber larger slows the velocity but increases over all power and is easier to load, I like .22 much better than .177, plus .22 has alot more over all options



  9. Dave,

    I found crosman premiers and beeman kodiaks to be the most accurate in both calibers, JSB pellets are known for their accuracy as well but Ive never used them so I don’t know any experience about the accuracy difference in both calibers.

    R.J.


  10. Dave,

    I have already answered the pellet velocity/accuracy question many times. Keep the velocity of a diabolo pellet under 900 f.p.s. for best velocity. Caliber doesn’t matter.

    At the lower limit, you simply get less range. For example, a 10-meter target rifle is very accurate at 10 meters, but not so accurate at 50 yards. The lower limit for consistent accuracy at that range is around 700 f.p.s., yet I shot a tight group of JSBs going about 500 f.p.s. with the Whiscombe. So go figure!

    B.B.


  11. lov-air rifles says why not increase the waist size of pellets for better acuracy in air rifles with higher velocities to increase flight stability. Every thing takes trial and error to get things right.


  12. All right, sat we found d fountain of money. What, in your opinion, is the best air rifle. Take into consideration the craftsmenship of builder, dedication to product, engineering expertise.



  13. BB,

    Is the 900fps the real world accurate velocity figure for one hole groups at 50 yards regardless of caliber? (with respect to diabolo lead pellets)

    What is the tolerance, 900 plus or minus someting value?

    Dave



  14. Dave,

    900 is the maximum velocity at which the best accuracy can be expected. Somethimes, though, accuracy does continue on past 1000 f.p.s. It’s not common, though, and I don’t ever figure on it.

    The best field target shooters in the world, which is to say the best airgun shooters in the world, stay under 900 f.p.s. But nothing is absolute.

    B.B.


  15. Dave,

    I have saved the posts with pictures. It depends on how you are saving them. If you are saving them as a web archive, your browser may require you to configure to same images. Explorer does that. But Safari saves them automatically.

    Check your browser’s settings.

    B.B.


  16. Did you see the new American Rifleman? Gamo had an advertisment for their 1250 which said “1000fps for lead pellets abs 1250 for Raptors”. Honesty in advertising or did the NRA say “not in our magazine”
    Ed



  17. I can’t understand the desire to hunt with .177cal pellets that many people seem to have. I’m an old hunter, used handguns for deer, rifles for elk ans antelope…and .22 cal pellets for sparrows to groundhogs. I’m not into it to see animals suffer. I’ve seen show where Gamo .177 air rifles were used on bobcats and Javelina..it is inexcusable.I just don’t understand where it comes from..a morbid fascination with death?
    Ed



  18. Hi BB,

    I own a .22 JW-80 that I purchased several years ago. It is an awesome work of engineering art!

    But I haven’t spent nearly enough time getting it to shoot as accurate as possible by adjusting the HOTS.

    When you were making HOTS adjustments, did you leave the muzzle-end of the HOTS off, leaving the threaded barrel weight exposed, turning the weight, and then shooting, without re-installing the HOTS muzzle-end until after all the shooting was done and the best accuracy achieved ?

    This would seem to take some of the tediousness out of the whole process, but I haven’t tried this method until after I read your blog and starting thinking about it.

    Also, my JW-80 did not come with any restrictors, so is it a simple process to make one’s own restrictors buy finding the appropriate threaded-hex set-screws and drilling holes ? What’s the thread size ?

    I really do need to spend more time with this wonderful rifle… Thanks!

    AirMojo


  19. AirMojo,

    I think I leave the cap off until finding the sweet spot. The cap is just light aluminum, and I figured it wouldn’;t affect the node too much.

    As for the size of the screw in the port, I don’t know. It’s about 1/8″ long – whatever that is in metric sizes, but I don’t have a metric thread gauge to tell.

    Wouldn’t Mac-1 know?

    Once you have them, yes, it is very easy to make the restrictors.

    B.B.


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