How barrel length affects velocity in a CO2 rifle

by B.B. Pelletier

Before we begin, Dr. Mirfee Ungier has answered a question about scope parallax and and the wearing of corrective eyewear. Here is her report.

Contacts always have you looking through the optical center of  the lens.  However, depending upon the glasses prescription, turning your head to view the target off the optical center of glasses will induce a variable amount of prism.  The stronger the glasses, the more prism might be induced.  Typically, someone with a correction under about 2.5 diopters will not have too much to worry about until they get into advanced competition.  People with higher degrees of refractive error would be better off in contact lenses. It should be noted that protective eyewear, i.e. safety glasses, are not an issue and should still be worn.

I thank Dr. Ungier for her explanation. I hope this clarifies the corrective eyewear situation for scope users.

Today’s test report comes at the request of reader Kyle, who wondered if there would be a velocity increase if he changed the 14.6-inch barrel in a Crosman 2250 to a 24-inch barrel. I said there would be at least a 100 f.p.s. increase, but Crosman said no. They said the barrel on the 2250 was optimum for that airgun.

I told Kyle that Crosman knows their guns better than I do, but that I would look back at my airgun literature and see if I couldn’t come up with some test data for him that shows the relationship of barrel length to velocity. In the October 1994 issue of The Airgun Letter I found a test where Tom Gaylord had cut the barrel of a Quackenbush CO2 rifle and recorded the velocities as he went. I think this is exactly what Kyle is looking for.

The gun
The airgun Gaylord used is the Quackenbush XL, a rifle with a removable 7-ounce CO2 reservoir. It had a .22 caliber Crosman 2200 pneumatic barrel that was 20.125 inches at the start of testing.

The test
The rifle was shot at 76 degrees F with 80 percent humidity. The chronograph was an Oehler 35P and the muzzle of the gun was positioned 6 feet from the start screen. Ten shots were fired with each of two pellets at each barrel length. The shots were spaced 1.5 minutes apart, to allow the rifle’s temperature to recycle after each shot. When the barrel was cut, the muzzle was reamed with a tapered reamer to remove any burrs. Since this was just a test of velocity, no accuracy was tested, so crowning the muzzle didn’t matter. The test started with a full CO2 tank which was refilled when the barrel got to the 15-inch length. The reservoir had been perviously tested to give not less than 125 shots at consistent velocity.

Barrel- Hobby- Kodiak
20″ ——– 645 ——– 548
19″ ——– 689 ——– 564
18″——– 680 ——— 562
17″——— 681 ——— 555
16″——– 671——— 547
15″——– 641——— 541
14″——– 639——— 518
13″——– 637——— 512

When the barrel was cut to 12 inches, it was then shorter than the gas reservoir underneath and the velocity dropped like a stone. Gaylord thought the gas might have reflected off the reservoir at the muzzle and caused some interference, so he ended the test at that point.

Well, I’m glad I revisited these results, because I didn’t remember them as well as I thought. My prediction that increasing a 15-inch barrel to 24 inches would bump the velocity by 100 f.p.s. was clearly wrong.

Gaylord also wrote that he was surprised that the 20 inch barrel was slower than the 19 and he prevailed on Quackenbush to send a 24-inch barrel to test. To his surprise, the 24-inch barrel was the slowest of all, even though it emitted a huge cloud of CO2 with each shot.

The fact that the 20-inch barrel was slower than the 19-inch shows that you cannot keep increasing the length of a barrel and hope to get higher velocity with CO2. Also note that the barrel performed about as good at 16 inches as it did at 20, and 15 inches wasn’t far behind.

The valve/hammer/spring of every CO2 gun will give different results that are peculiar to that setup, and different barrels will also perform differently but this is the trend they will all exhibit. The point of optimum velocity will change as the setup changes, but the relationship will remain the same.

I have some thoughts about how barrel length affects velocity with pneumatics, too. Perhaps in a future post.

53 thoughts on “How barrel length affects velocity in a CO2 rifle



  1. BB – I spent some time with my new scope over the weekend and went to remount it so I could use a beefier shim. I was surprised that the scope had slipped back so the front ring was hitting the back of the objective (? – where the tube opens to the front of the scope). I reinstalled everything and rechecked tightness on the mounting rings and all seemed good. I used a piece of metal ducting to beef up the shim as well.

    What I did find was that the elevation adjustment seems to be a bit wonky. I used a laser sight level and when clicking the adjustment, it seems like there are some clicks that don’t move the elevation, like there are broken teeth in a gear mechanism. I’m assuming that is not normal – right?

    The other thing I found was you have to get a certain tension on that spring before the elevation actually changes. I tried to shim so I would be maybe 25% into the adjustment range at a short distance to give me room to adjust for further distances (spring at ~ 75% loose). Hope that was right!
    Ozark


  2. Wow! Very interesting and unexpected. The velocity sure dropped a lot with just that 1″ difference! Thanks for the article BB!

    .22 multi-shot


  3. Ozark,

    Yes, there does have to be some tension on the spring before the adjustments will move. How much varies from scope brand to scope brand, but they all need some tension.

    There is a new scope design that uses cams and not erector tube springs to move the tube. They say it has positive control throughout the entire adjustment range.

    As for the broken teeth – that’s just what it could be! I’d have to acutually see the scope to tell, but it sounds like you know what you’rte doing.

    What kind of scope is this?

    B.B.


  4. Effect of barrel length on velocity ….

    Increasing barrel length serves to increase the time the bullet is under pressure from the expanding propellant gases. The pressure is lowest as the bullet nears the end of the barrel.

    Increasing the barrel length also has another effect. The bullet experiences bore friction longer.

    Take these two points together and you can figure out most scenarios. For the Quackenbush XL, with the 20″ barrel the retarding frictional forces just manage to get the better of the expanding gas pressure. The 24″ would obviously slow down the pellet even more.

    There is an optimum barrel length at which the pellet speed will be highest. Go above that and the addt. friction will slow you down. Go below that and you wont utilise a significant amount of the gas pressure (which will be wasted as muzzle blast) and you’ll again be slower. And thats 19″ for the DAQ XL.

    Thank you for reading.


  5. B.B. great posts lately, very interesting. I was hoping to find out when we might see the next post on the Berretta CX-4 Storm. My son and I are quite interested in this rifle and are dying to find out your experience with accuracy.

    Thanks,

    LS & son


  6. B.B. I was reflecting on the question from the gentleman with the 2250 that triggered todays post and I suspect that the information he got from Crosman was pretty accurate. If memory serves the 2260 has a 20″ barrel and is only rated at 50 fps more than the 2250 and I have to assume that it’s valve has been optimized by Crosman to reach that speed. 2250 modification specialist such as Crooked Barn employ modified valves such as the Boss (B&A)and do not end up getting that much more speed while consuming a great deal more CO2 per shot. To be honest, I remain quite impressed with the efficiency/performance Crosman gets from there current valve/barrel combinations with products they have been producing for a while (like the 2260, 2250 ect.)Just because they are inexpensive does not mean they are not very well engineered.

    LS



  7. LoneShooter & son,

    I should get to the CX-4 accuracy this week. I’m just as interested as you two.

    I agree that Crosman does very good engineering. That’s been true for many decades. They have always employed good engineers and they let them run with the ball. The 2300 S&T pistols are proof of that.

    I think we can all learn a lot from them.

    B.B.



  8. i think the 2260 has a 24″ barrel. someone correct me if i’m wrong.
    bb i’m hoping you share your thoughts concerning barrel length and fps in regards to pneumatics “sooner than later” because i’m about to do a similar mod, and am wondering if its worthwhile.
    thanks




  9. ok i posted on Sunday about the Daisy 753 and now i have a hard choice to make. I have 3 ideas for air guns

    CROSMAN CHALLENGER 2000 by Crosman
    AVANTI 753 by Daisy
    IZH 46M Match pistol by IZH-Baikal

    i am 16 years old and i am looking for something that will last for a long time and i will not out grow and the quieter the better. can you please give your input on my choices and any other ideas my price goes to $360. i know all these are diffren but they all follow my ideas except i worry i might out grow the crosman. So can you please help.


  10. I vote for the Daisy 753, though the 853 is the better bargain. Both are identical except for the stock.

    I don’t recommend the IZH 46M because pistols are much harder to shoot than rifles.

    Both the 753 and the 46M are single-stroke pneumatics. Keep their pump cups oiled with Crosman Pellgunoil and they will last a very long time. I have seen 853s last over 20 years with hard club use. My 46 is 8 years old.

    I do not recommend the Crosman because it has a sporting barrel and isn’t that accurate. It actually has a better trigger than the Daisys, but only get it is you want a rifle to plink with – something to put a scope one. Get a Daisy if you really want to shoot targets.

    B.B.



  11. Hello B.B.,

    Very interesting blog today, as usual. I am really surprised there was so much difference between 20″ vs 19″ (an actual INCREASE in fps with one inch less).

    You don’t think there was any restriction or choking at the end of the original barrel, that would have slowed the pellets down with 20″ barrel? Or you don’t think the reaming of the cut barrel(s) lessened friction at the end, which wasn’t present with the original/20″ barrel?

    Thanks


  12. B.B.–Scott298-well this is about the 15th time I tried to get thru-my question was in several of the catalogs -cabela’s and hunting magazines they offer a multitude of scopes with all types of qualities. Now it’s my understanding that a scope made for a springer will work on centerfire,rimfire, and black powder. Wouldn’t these companies make more money if the specified which ones worked in these air guns, or is there just a limited number of companies making air gun scopes. It’s fustrating going over page after page and not finding any listing this qualification–thanks-Scott


  13. Hi BB,

    I’m curious how much more accurate with BBs my Crosman 760 is than my PPK/S pistol. I know that the 760′s longer sight radius and perhaps the blowback effect of the pistol are factors, but the accuracy difference of the two guns really surprises me. I shoot at 15′ indoors with both guns, and I use two pumps on the 760 (more pumps raises the point of impact but doesn’t seem to affect accuracy at that range).

    Is there any other factor I’m unaware of that causes such disparate results between the two guns?

    I absolutely LOVE the trigger pull and functioning of the PPK/S but it’s ‘accuracy’ is always a let-down…especially since one shot will go one place and subsequent shots will often go somewhere completely different (within roughly a 2″ area but often I’ll get some really strange flyers that open the spread to 5 or so inches).

    BTW, I’m an experienced airgun target shooter with pistol and rifle, and most of my indoor shooting is from a steady rest.

    Thanks,

    -Joe


  14. SquirrelKiller,

    I don’t know if there was any special influence that the 20-inch barrel might have had, but as I noted, the 24-inch went even slower. How much slower I don’t know.

    B.B.


  15. Scott298,

    I don’t know what problem you are having getting through to the blog, but your question is too good not to serve as a blog topic.

    What makes an airgun scope? Next week

    B.B.



  16. I have two questions that have probably already been answered, but I’d appreciate knowing “why?”

    1. Golf balls have dimples because the dimples improve their accuracy and the length of golfers’ drives. Why aren’t BBs dimpled for the same benefit?

    2. Accurate air soft guns have a rubber or plastic strip in the top of the muzzle ends of their barrels to give backspin to the pellets, allowing them to offset the pull of gravity with some degree of lift. Why aren’t BB guns similarly equipped?

    Thanks for this wonderful blog!

    fflincher


  17. fflincher,

    The simple answer ius neither thing has been tried.

    Except one of them has. Gary Barnes developed a way to score the ourside of a round ball uniformly with random scratches. He used a window screen to do it, so he called it screening the balls. Screened balls were always nor accurate than smooth balls. He did it to increase the ball’s diameter, which it also did, but screened balls were very accurate.

    As for the Hop Up, I doubt a rubber bumper would stand up to being hit by a BB repeated times. That’s probably why it hasn’t been done. If someone could figure a way to do it, it would probably work.

    B.B.


  18. Vaguely related to CO2 velocity and barrel length: The Drozd could use multiple valves and CO2 cylinders to avoid freezing up. There could be three separate bottles and valves and a 3 shot burst would consist of each going off in series.


  19. B.B.–Scott298-had to type my blog 4 times and hit the publish button at least 20 times-been job hunting-that,s not been going too well so I guess today why should be any better! Keep the faith-Scott


  20. BB – I intermittently have trouble posting as well. Most of the time, I’ve got to enter the “word verification” at least twice. On occasion, the “word verification” doesn’t even come up.

    As for hop-up on a steel BB, I suspect that there’s a few good reasons for the lack of it:

    1) It isn’t as necessary. Airsoft BB’s lose velocity FAST after they come out of the muzzle. Much faster than steel BB’s. As a result, they spend a lot more time in flight to the target (even with the same MV), and thus tend to drop faster.

    2) I doubt that backspin would be nearly as effective on a steel BB. The force of gravity acting on a steel BB is about 20x greater than that acting on a heavy .25gr airsoft BB, so the aerodynamic effects of the backspin will be far less effective. Also, the steel BB is smaller, which means there’s less of that effect to begin with.

    3) Franky, I’m not sure that hop-up really improves accuracy that much. In order to be consistent, the BB has to leave the barrel with the exact same rotational velocity each and every shot. This means that the coefficient of friction between the rubber and the BB has to be very consistent… and THAT’S dependent on a number of variables (lube in the barrel, surface finish of the BB, etc.). And since backspin is related to velocity, variations in velocity will cause larger than normal vertical variations in the BB’s flight path.

    Just my guesses, anyway.


  21. regarding your point #2, gravity works the same on all objects regardless of weight. at least, here on earth. aerodynamics are a separate issue.


  22. B.B.–Scott298–If you have to have one gun and you were going to youse it for target, plinking, and the occasional squirrel or crow and the gun has to be the tx200. and you would use only heavy pellets in .177 or a variety of pellets in .22 which would you opt for and why–now remember your only choice is the air arms. I would rea;;y appreciate your comments and knowledge–thanks Scott


  23. BB.

    I cant say all i have to say about the airwolf after only a day of shooting (tanks full). The dive shop filled it to 4500 but is was like 4300 after cooling (heat expantion / cold contraction). Moving on…

    What a tack driver! I was using kodiaks today and was only wanting to get it close because i was using a towel for a bench. Never went over a an inch for sure. I would say 1/2 inch was a normal group (just guessing). I will bench shoot it soon and we will see so i’ll stop her on accuracy for now.

    I hope kodiaks perform as well as JSB’s because i want that extra power. I think the kodiaks will be less accurate but a head shots a head shot and the squerrels know that. Im not bench shooting squerrels so the gun will be more accurate than me with any pellet.

    On to power! It shoots kodiaks at about 42 foot pounds. I only put like three shots into the chrony so i wont make any claims about its shot to shot spre. Out of curiosity i will try a eun jins. I have all these pellets so i can do it tomarrow. I have lots of free time as you can tell.

    MOST IMPORTANT…is it heavy in general, front heavy, or awkward to hold?

    Ok, its a bit heavy (in general) but is perfectly balenced with my big burris black diamond scope on it. If i put a compact scope on it would be front heavy. I shot it off-hand and it felt wonderful. The theoben is different but no better. The theoben is 3 pounds lighter for starters.

    I am almost 4,000$ and two months into this gun and finaly have its going. WORTH MORE THAN EVERY PENNY (so far but time will tell).

    Heres what compeled me to say that:

    I filled my condor today, put a kodiak in, pulled the trigger and click the hammer goes and makes makes some twang KU-cKung—cho screw up sound and doesent fire, thats the end of that. I am laghing as i write this. I liked it before that.

    Do I buy another condor? Naa. Fun while it lasted but its over (thats what she said lol jk).

    To sum it up- I LOVE MY AIRWOLF BUT thats what i said about my condor untill it broke.

    This was not very informing but its just a first imprestion. I will have a post on accuracy one on shot consistancy and much more. I cant compete with bb.

    -sumo


  24. Holy Smokes! I just was reading about that dragon slayer .50 cal on the blog – what the heck do you use it for? Elephants?? We talk about .177 and .22 for critters… but with 192 fpe, what kind of game is prey?


  25. Well, you can hunt coyotes and larger critters if you like, but who says you can’t just enjoy shooting at targets? Owning one of these mnodern pneumatic monsters is a treat, since they were exclusive for four centuries. It’s as though Ferraris were just marked down to $20K.

    B.B.


  26. Sumo,

    Well you have a new love! That’s great. Only don’t forget that your Condor has a lifetime warranty, so if you don’t like it anymore, at least you can get it fixed free so you can sell it.

    B.B.


  27. Scott,

    I would get the .177 for your uses, and don’t just shoot heavy pellets. Test a lot of good ones until you know the best one, then lay in a supply and don’t shoot another pellet.

    B.B.


  28. Sumo

    i have done much testing with my Condor and have come accross a number of pellets you may like to try:
    Piledrivers 30g, great BC, not very accurate Avg 70.59ft-lbs
    Eley Wasp Magnum 20g, VERY accuracte, best BC (.1074) Avg 66.35ft-lbs.
    Daystate High Impact, 40g VERY TIGHT FIT, accurate Avg 73.31ft-lbs
    Varminter HPs 39.5g VERY TIGHT FIT, accurate, Avg 73.91ft-lbs

    If you want power, these are the pellets. Eun Jin Avg 63.69ft-lbs, are accurate but their BC is much worse, meaning POI power is less than half the bad boys above

    I hope that helps



  29. I will send m y condor to be fix. I dont think i will sell it. I would fear it breaks again, then somone is mad at me. I have spent $1500 on that thing.

    I like the eun jins and kodiaks best.

    Well i have like 4000 psi in my tank. I think i will go start up the 707. By for now.

    -sumo


  30. Anonymous…

    The FORCE of gravity is not the same on all objects regardless of weight… in fact, the very definition of weight IS the force of gravity that acts on an object. If an object that weighs twice , it literally means that gravity is pulling on it twice as hard.

    A .25gr BB needs .25gr of aerodynamic lift in order to keep it in level flight. If a steel BB of the same dimensions and surface finish was shot with the same linear and rotational velocities (and thus generating the same amount of lift), it would be .25gr of lift vs. 5gr or weight.

    If you take a gun with hop-up optimised for .2gr BB’s and shoot .25′s in it, the BB’s will drop faster. If you shoot .12′s in it, they’ll actually sail upwards because lift is greater than weight.

    If aerodynamics were a separate issue from weight, any sized airplane would be able to lift any load.


  31. “It comes down to the fit of the BB in the barrel. The PPK/S has a wide bore to tolerate all BBs and still function. The 760 is tighter and it shows.”

    I didn’t realize that BBs came in such wide tolerances. Why don’t they then cause a problem in the 760s? Or is it just the European BBs that are (I assume) sometimes thicker? Or (duh–I just now noticed the ‘and still function’ part), does the PPK/S require less tolerance because the 760 doesn’t have that cute blowback feature?

    Y’know, BB guns seemed a whole lot simpler to use back when I was a kid.

    -Joe


  32. Joe,

    Yep, blowback is thwe reason. And it isn’t that the BBs don’t fit in the bores. It’s the need to get a thin plastic stick magazine to line up with the hole in the rear of the barrel, so the BB doesn’t hit the breech face.

    It’s an alignment issue, not a bore fit issue.

    B.B.



  33. I’ve a mess of questions; can you take the stock off the 2250B for storage in a cheap double-pistol case? When will the Benjamin AS392T become in stock? What is the effective varminting range of a Crosman 1377C tricked out with a stock, Reflex sight, and Kodiaks? Also, which is a better scope for a Crosman 2260, or if you can think of an similiar priced scope, please elaborate; CenterPoint 4x32mm Compact or Leapers Tactedge 4x40mm?

    Once again flip-flopping,

    14 in Fla

    P.S

    Price range is boosted to $200 max(figured I’d get that much by Christmas)



  34. Would I need to make a cover for the AirSource canister on a 2250XT? I’m considering it because of its sheer volume of CO2, but if the CO2 port/CO2 canister has a chance of bending or even breaking off entirely, I’d need to use sheet plastic, cut it into four pieces, and make an easy disassembly so I can replace the AirSource.

    At a three prong fork in the road,

    14 in Fla

    P.S, Should I use whatever I get with a scope instead of a Reflex sight? The range is the same, 30-40 yards. My vision is about 20/27 corrected. Without….well, I’ll say I can’t even see the vision test board letters, any of them.


  35. 14 in Fla,

    Not much chance of bending the AoirSource cartridge. Don’t cover it.

    Go for a scope that has a diopter adjustment. Ask if the specs don’t indicate it. Then adjust the scope and you should be okay.

    B.B.


  36. Can you point out scopes that have such an adjustment? Is a diopter adjustment simply a focusing eyepiece, or is it a specialty type of thing?

    14 in Fla



  37. Can you estimate how much power I’d lose with a 2260 or 2250(Powerlet) and a 2250XT(AirSource) in 59 degree weather? I’m trying to see if I can prevent pigeons flying around my house, pooping on various objects(happened one day, had to clean up…not anymore, after I acquire an airgun).

    14 in Fla



  38. I got a 2250 at crosman custom shop, and it has 24″ barrel. I wonder if the performance should be the same as 2260. Are the action parts of all 22xx actually the same? Another problem I am facing is valve lock. I have weaker shots from the beginning, but after a while it starts blasting off. Do you think it will break in? What would you suggest?


  39. The power should be similar, but perhaps not exactly the same.

    As for the weak first shots, that cannot be valve lock, because CO2 pressure never changes. It’s the same start to finish, except for temperature variations.

    What are the chronograph readings? Can you give me a string of shot velocities, so I can watch the velocity curve?

    B.B.


  40. Hi,this is very interesting.I have a crosman 22xx(2250)Ive just started getting into modding air guns.I dont have a 14.6″ barrel on my 22xx as i just converted it with a 2250 tube from a 2240.So im using the 2240 barrel on my 2250 as a mini mini carbine.Ive made a few modifications,i put a new power spring in it which is 50% stronger than the original.I also put an extended probe in it to push the pellet past the pellet port for better consistancy.I also got the crosman long steel breech.I can get 24 consistant power shots from a 12 gram co2 out of my 22xx with a 7.5″ barrel.I dont have a chronograph so i have no idea what velocity the gun is shooting at ,at the moment.Obviously the energy of the gun has increased with the modifications,im getting a stronger burst of co2 behind the pellet not on top of the pellet.I used to be able to get 40 shots out of a 12 gram co2 now i can only get 24.

    Is there any way i can judge how much more power im getting out of the gun without a chrony? I really want to know how much power im getting out of the gun now with the mods.It certainly sound more powerfull and i can just feel it,if this makes sence.


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