Different types of rifling

by B.B. Pelletier

This will be limited to the common types of rifling found in modern airguns. I can’t possibly cover all the types of rifling in this posting – or even in this entire blog! There are several books written on this subject, so if you are interested in pursuing the subject further, I recommend you do a search in the used book stores online. I’m doing this post because several people have asked why it’s okay to shoot both BBs and pellets in some guns but not in others.

Lands and grooves
Lands and grooves are a common type of rifling. The lands are square-cornered ridges that raise up from the grooves. They are cut in a gentle spiral, so they impart a spin to the projectile. The twist rate is how many inches of bore it takes for the projectile to make one complete rotation, so one turn in 10 inches of twist (1:10) means the rifling (and anything that passes through it) rotates once every ten inches. A one-in-sixteen twist rate (1:16) that is standard for .22 long rifle is also very common in airguns of all calibers. Because the diabolo shape also helps stabilize the pellet, it doesn’t rely entirely on the rifling, so the twist rate isn’t as critical.

Some big bore air rifles have traditional land-and-groove rifling, which makes loading difficult if you try to seat the bullet into the bore (because the lands are taller and offer greater resistance). Makers compensate for that by tapering the lands at the breech.


Traditional land-and-groove rifling looks like this in cross section.

Microgroove lands and grooves
Microgroove is a trade name of Marlin. It was trademarked in the early 1950s, but the type of rifling has been known since at least the late 19th century. If he didn’t invent the idea, Harry Pope perfected it. Microgroove rifling refers to the conventional land-and-groove pattern where the height of the lands is lower, and the width is narrower. While this isn’t all that Pope created, it is an important part. Shallower, thinner rifling means less deformation of the bullet/pellet, which improves accuracy.

Airguns are perfect for microgrooves, because they also offer less resistance when the pellet is engraved by the rifling and help seal the bore better because there is less depth and width to seal. The simplest kind of microgroove rifling is just shallower and thinner lands of the land-and-groove type. Twelve lands are common, but sometimes six are used, especially in .22 caliber. Where normal rifling lands are 0.005″ high, microgrooves might only be 0.0015″ high.

Polygonal rifling
Barrels that shoot both BBs and pellets often have polygonal rifling. This is an old type that dates back to the 19th century, but it is also used by some very modern makers of firearms. Instead of the bore being perfectly round, it is a polygon. It still twists just like the other kinds of rifling, only the entire polygonal shape twists.


This drawing is exaggerated to better show the concept of polygonal rifling.

While the BB is still loose in any barrel that also accommodates a .177 pellet, the air blowby does no real harm. There are no lands to damage in polygonal rifling. However, accuracy is generally not as good as in a dedicated microgrooved barrel shooting lead pellets only. The dual ammunition is a good sales point in lower-priced airguns, and the much lighter steel BBs fly faster regardless of the amount of air that blows by. To compare this type of rifling to what is possible with a BB in a smoothbore barrel, Daisy’s Avanti Cyampion 499 will group 10 shots in 0.20″ at 16 feet, while a polygonal barrel might group BBs in one inch or larger at the same range.

For this reason, I call all such dual ammunition barrels a compromise. Like the .357 Magnum revolvers that also have cylinders for 9MM, neither one will be as accurate as a gun that is dedicated to just one type.

28 thoughts on “Different types of rifling

  1. B.B.

    I had a question on this subject. When you talk about a 1:16 twist rate, why do they make it spin this much? If they made it spin say, 1:2, would that be making the bullet spin so fast that it would throw it off course? Again, if it was less of a spin rate, would this make it not spin enough to stabalize it? Just curious.
    Thanks,

    lama


  2. lama,

    It has to do with what stabilizes the projectile in flight. 1:16 stabilizes a 40-grain bullet at around 1,000 f.p.s.

    When a football is thrown, it is spun to stabilize it. The “spiral pass”?

    If this is an interesting subject for you, you should do some reading on it. For example, why were all rifles made by the Hawken brothers rifled with a 1:48 twist rate? Answer – that was the only rate they could rifle them! They were limited by their machinery.

    When the U.S. first fielded the M-16, it went into battle with a 1:12 twist rate. You couldn’t hit a barn with it past 300 yards. Today we have 1:9 and 1:8 rates for the same rifle. It’s still not a great shooter, but it’s a heck of a long way from the dog it once was.

    Twist rates are both a science and an art. They have to be worked out with formulae and then rigorously tested. Want to know the best, most-tested bullet, twist rate probably of all time? The .458 405-grain bullet for the .45 Government (45/70). Thery tested it to distraction, because in those days they were concerned with long-range accuracy. They actually wanted to go with a .50 caliber at first, but the .45 out-performed it at distance.

    B.B.


  3. B.B.
    I think in an old post, you mentioned something about you didn’t like the M-16 because you used it in the army, and you liked the M-14 because you used it in the army also. Can you explain what you meant by that? Was it due to accuracy reasons?

    Thanks


  4. B.B. what should i do if im having trouble keeping the mount screws tight on my air rifle? is their any way to solve this problem or should i look for a different set of mounts?



  5. M16,

    Accuracy and killing power. Our Army is going back to the M14 in the middle east because their M4 carbine that looks so neat isn’t doing the job they need. Same thing with the 9mm handgun. It’s too puny for combat, and the Army is looking to go back to a .45 ACP.

    We have done this before. In the Phillipines at the turn of the 20th century we discovered the .38 Colt was insufficient for combat. .45 Colt revolvers were issed to take up the slack and the Army went into lengthy testing that resulted in the M1911 Colt pistol.

    The Brits did the same thing in WWII when they replaced the .455 Webley with a .380. It was underpowered and insufficient for real combat.

    In peacetime the bean counters always go for the lightweight underpowered guns, then they load a soldier down with 100 pounds of crap equipment. Just follow a soldier after he’s been in combat for two weeks and he will have what works on him. The rest of the crap will be abandoned.

    B.B.

    B.B.


  6. thanks for the advice B.B., ill try that. if i own a patriot would you recommend searching online for the locktite in heavy strenth, or should i just buy the medium strenght that pyramyd offers?


  7. B.B is right, rifling has been tested quite thouroghly by many organizations, but since we keep developing more and better ammunition, we still have more to learn. And to help with your question Mr. Lama, a very fast rifling in an air rifle merely leads to partial destruction of the skirt, which of course where most of the accuracy of the pellet comes from. In firearms it leads to desruction of the bullet almost at the muzzle, but air rifles do not acheive the same velocity so mangling the skirt is all we have to worry about. Gain-twist rifling can get a very fast spin in a short barrel without extreme deformation and could get an extreme spin rate in an air rifle barrel, but I doubt it would contribute anything as the spin woud do less to accuracy than the shape of the skirt because of the size of the pellet, shape, I could go on.
    As always, an impressive blog, B.B., thanks.

    Mr. Watch


  8. bb, i remember reading about your experiences with the 631. i remember that gun having microgrooves (i would presume, from the _tiny_lands and grooves)
    the diana a own now has much deeper rifling. it seems like the grooves are very small while the lands are very large. is his an attempt to minimize deformation? and, after retriving pellets i’ve shot, it looks like the deformation is minimal. in two identical guns, with identical quality barrels, which would have the accuracy advantage, the microgroove barrel, or the land and groove? it cant be much, the rifling only leaves a few marks on the skirt!


  9. TOO RIGHT BB!
    YOUR OBSERVATIONS
    ON THE NATURE OF MILITARY ARMS
    HOLD MUCH TRUTH.THE MENTALITY OF
    “IF LARGE WORKS WELL”, “SMALLER
    WILL WORK BETTER” HAS BEEN REPEATED
    OVER AND OVER. INPUT FROM THE INDIVIDUAL IN THE THE FIELD HAS ALWAYS BEEN UNDERRATED, IF NOT ENTIRLY IGNORED. THE POOR MEN WHO
    WERE FORCED TO SURRENDER THEIR M-14′S IN THE ‘NAM IN 1965 KNEW IT
    AND ANYONE WHO HAS BEEN EQUIPPED WITH VIRTUALLY -ANY- 7.62X51 NATO
    [.308 WINCHESTER,ALMOST,SLIGHT DIF-
    FERENCES IN CASE DIMENSIONS]RIFLE
    SINCE HOLDS ONTO IT LIKE HIS LIFE DEPENDS ON IT…DUH!!! THIS COUNTRY
    HAD THE TWO BEST PERSONAL FIREARMS DEVELOPED AS OF 1964. THE 1911AI IN .45 ACP AND THE M-14 IN 7.62X51 NATO {SEMI-AUTO -ONLY-]. LET US ALL HOPE FERVENTLY, SANS RESERVATION,
    THAT WE RETURN TO THEM WITH VERY FEW ALTERATIONS. FOR THE COUNTRY
    AND THE PEOPLE WHO SERVE IN THE WAR.
    -FLINTLOCK-




  10. diana,

    Lands and grooves and microgrooved rifling are the same. The microgroove is just shallower. The Diana is probably microgroove too, but it may be a half-thousandth deeper.

    It’s impossible to predict accurcy from the rifling style, so I really can’t comment on your question.

    B.B.


  11. BB,
    ABOUT THAT GUY WHO USE SCOPE ON MULTI PUMP PNEUMATIC, WHERE DO U THINK U SHOULD HOLD UR RIFLE WHEN PUMPING WHILE USING A SCOPE?
    WHEN I’M PUMPING MY BENJAMIN, I USED FIST TO FIST, MEANING I HOLD THE RIFLE AT THE BARREL ABOVE THE BACK STOCK WHEN PUMPING. CAN DOING THAT DAMAGE OR BEND MY GUN BARREL?

    HAQUE


  12. O,
    AND IS THERE A SCOPE U CAN RECOMEND THAT IS SHORT ENOUGH FOR A PUMP PNEUMATIC TO LEAVE ROOM FOR HOLDING WHILE PUMPING IT?
    WHAT IS THE DISADVANTAGES OF USING A SHORT SCOPE COMPARE TO A LONGER ONE?

    HAQUE


  13. Haque,

    Your method of pumping is common. Many shooters do the same. It shouldn’t bend the barrel.

    There may be a new scout scope coming that will allow you to mount it on the barrel and still have the correct eye reliefe.

    B.B.


  14. BB,
    I have a question that is perhaps off the current discussion….How do you determine the energy in a pellet vs distance(.177 vs .22) is there a rule of thumb or rough calculation ? I’m interested in selecting between the TX200 (.177 based on your review), RWS 350 (.22), RWS48 (.22), RWS54 (.22), HW97 (.177 but is only carbine available ?)

    I’m interested in long range accuracy, ease of shooting and noise (not really familiar with higher power airguns compared to 22 rimfires). I’m not interested in the power necessary to take racoons or crows.


  15. By all means, get the TX200 in .177. It is worlds more refined than the others and much quieter.

    As for long-range accuracy, it can beat all the others by a small amount at 50 yards.

    B.B.


  16. BB,
    Oh, I forgot to ask an additional question….if you say TX200, then the question would be is it a crime to save the extra money and go with the beech stock rather than the walnut ?

    Thanks



  17. BB,

    Back to the energy question…With the TX200 in .177 do you know the approximate energy it would have at 50 yds ? Also, I have a Bushnell Sportsman 3-9x32mm Scope w/Adjustable Objective I used to use on 22 rimfire, would this work or get damaged on a springer like the TX200 ?

    Thanks for the advice.


  18. Starting at 14-15 foot-pounds it would have 8-9 foot-pounds at 450 yards. It all depends on the ballistic coeffcient of the pellet.

    B.B.


  19. BB,

    Thanks for the info. This blog and your reviews really helped me.

    Yep, I knew the exact number would depend on the specifics of the pellet, but was just looking for a ballpark figure since I was unsure how fast it lost energy further out. That sounds like it would likely be sufficient for small rodents if the need would ever arise. But I know I’m not a good enough shot to hit one at 450 yds !!! Thanks again will be ordering later today.

    The PyramidAir site has the muzzle velocity calculator somewhat buried so I took their formula’s and plugged into Excel spreadsheet to give myself a little education on the various guns and pellets available in my decision making process. Per your review of the TX200.

    Thanks again



  20. my friend left my gun cocked and loaded for several days without my knowledge. i didnt realize this until maybe 5 or 6 days later when i shot my gun again. it seems weaker. do you think my main spring was significantly weakened by this? and is there anything i can do?


  21. It may indeed have made it weaker, but for a week, I wouldn’t look to see a drop of more than 60-90fps.

    I do know that some people leave their Magnum powered springer cocked over night to help reduce some twang, and make it more controlable for accuracy.

    The only real way to tell is to chrongraph it.

    TS




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