Hey guys, I have been otherwise occupied for some time and just now getten back to my AG's. Got a question that maybe has been answered many times but I'll start a fresh thread here. At what length does the length of a barrel become a drag on the pellet in a Co2 gun. I can see that much is wadted on a short barrel and volocities are higher with a longer barrel, But there is a point that the psi's are dropping. ???
This is a decent resource that addresses your specific question.
http://www.pyramydair.com/blog/2007/07/how-barrel-length-affects-velocity-in.html (http://www.pyramydair.com/blog/2007/07/how-barrel-length-affects-velocity-in.html)
I wonder if 18" is best why Crosman makes 24" barrels. Seems if you have enough power the longer the better.
Makes me wonder.... ???
Do some searching around here on the board, several of us had done some testing with various lengths.
Quote from: BillK on June 16, 2014, 08:44:37 PM
I wonder if 18" is best why Crosman makes 24" barrels. Seems if you have enough power the longer the better.
Makes me wonder.... ???
Going to guess that after 18", there is no more additional expanding pressure from the initial blast of CO2 out of the valve, and the final 6" of barrel length adds drag to a non-accelerating pellet.
Quote from: breakfastchef on June 16, 2014, 11:04:24 PM
Going to guess that after 18", there is no more additional expanding pressure from the initial blast of CO2 out of the valve, and the final 6" of barrel length adds drag to a non-accelerating pellet.
well said ... :-*
Purrty-much... the gas expansion has a finite level (barrel length) given the small volume of co2 available.
Perhaps .22 is different from .177 . Back in Nov. 2013 Airriflenut was changing/checking barrels on his .177. The 24" shot 703fps while the 18" shot 677fps.
I guess I'll have to put an 18" barrel on my 2260 and see what the difference is.
Seems if the valve is low power than a longer barrel would/could slow down a pellet from the added friction of the longer barrel. So, is a 2240 valve powerful enough for a 24" barrel?
This is getting above my ability to conceptionalize.
. :-[
The best I ever got out shooting CO2 was a 724fps average out of a 24" .22 barrel shooting 14.3gr. pellets. The rifle was bulk fed using a 9oz. bottle and an Archer tank block mounted with 4 screws. The valve was a gas hog and I got just 6 shots out of a 12 gram cartridge. Using a shorter barrel it couldn't break 700fps. No I didn't get a hundred of shots either. Not to efficient build. The CO2 usage was too high for the fps I got. I think I used a lot of the parts for my 1st Disco build!
Glen
Tinker I believe that those are the key words bulk fed or hpa.I think (my own opinion here)having not done any testing that a higher volume power supply would enhance the longer length barrel rather than hinder it.And with a 12 gram power supply you get so much power behind the pellet then that is it.
Perhaps the longer 24" barrel is for the sake of accuracy, if not additional power. Though I can't imagine there being much of an appreciable difference for either. With the 24" being simply too long and unwieldy for such a small platform, I would never get one anyway.
Yes the key was bulk fed Tom. Even with the 24" barrel she spewed CO2 out the barrel just like a stock 2240 with a fresh cartridge with every shot!
Thanks for the input guys. I kinda had the feeling that at some point, longer barrel lengths would be a drag cause the UMFF is gone.
i was just saying what I was thinking like I said it was my opinion an untested one at that.
Tinker noted the key fundamentals with co2. It's a fine line between optimum velocity and shot count, especially with co2. With a nominal pressure of 830 psi regardless of volume, the amount of gas used per shot starts to become "waste" as a function of "filling" the longer barrel for each shot.
On barrel length vs. accuracy, many of the best quality airguns have 12" and 14" barrels and are one-hole shooters, (HW, FX, Air Force etc).
i read somewhere that 3" of barrel is all that is needed to achieve enough spin for accuracy
ped
Quote from: ped on June 19, 2014, 11:43:31 AM
i read somewhere that 3" of barrel is all that is needed to achieve enough spin for accuracy
ped
Well... don't know what the right number is but, FX air rifles have the Smooth Twist barrel which is just that, 10 inches of smooth bore and the last few inches rifled.
Freddy Axelson (FX) is a clever guy so I'm guessing it works?
As I've said on more than one occasion, I'm neither a firearms engineer nor an air gun expert but these forums (be it good or bad) allow any member to state their opinion as long as it's done in a civil manner.
As stated by many of the replies so far, barrel length is only one of several factors that contribute to pellet velocity. Pellet weight is certainly a factor, as is valve output and whether you're on the first shot of a CO2 cart or near the last.
RE: barrel length, friction is definitely a factor. Assuming the same condition of the bore, the effect of barrel friction on a pellet is less with a shorter barrel than with a longer barrel (That's probably pretty obvious to most folks). However, I don't think that friction becomes a major factor until the barrel length becomes excessive. In between the extremes of too short and too long, the barrel's length has it's effect on velocity by allowing the expanding gas from the CO2 cart to continue to accelerate the pellet until it exits the muzzle.
RE: pellet weight, basic physics (Newton's 2nd Law of Motion F=ma) tells us that, with other factors being equal, when the same force (F) i.e. CO2 valve output, is applied to a lighter pellet (m), the acceleration (a) will be greater.
RE: valve output. For many of us this will be a constant as no attempt will be made to "mod" the valve to increase it's output. Many, of course, will apply a great number of mods to increase valve output. Lighter internal springs, heavier hammer springs, porting and polishing the gas pathway are among the most common.
RE: CO2 cartridges, they are, for the most part, a constant also. The CO2 under pressure (~800 psi) in the cartridges exists as a liquid. This allows the output pressure to remain constant until the CO2 liquid is depleted. This, of course, makes CO2 a perfect gas for this purpose. Gases that liquefy at much higher pressures (and / or lower temps) like air, oxygen and nitrogen are not suitable in this situation (i.e. gas filled cartridges).
Anyway, back to the barrel length issue. Assuming standard CO2 power source, optimum barrel length would be that where the valve output is no longer accelerating the pellet at the point that it leaves the barrel. Easy to say, not so easy figure out. Especially if a variety of different weight pellets are used. Basically, it's a trial and error process. Fortunately, most of the leg work has already been done! Most of the searching that I did indicated that for the 2240 basic air gun, an 18" would be an "optimum" length. That is what I have on my 2240 .177cal hybrid. I've yet to run it over my chrony so hard data is yet to come.
Opinions are worth what you pay for them and since this is a free forum, let the reader beware ;). I'm just sayin'.
Flex
Six mo. ago I got a 2250XE w/24" barrel. It was a good barrel @ 5 meters or so but at 20 meters it was all over the place. So I changed it for an 18". I prefer that length anyway. The 18" is dead on at 100'. This isn't about accuracy, just letting you know why the change.
I also got one of Davios med. hot, not full blown boss type valves.
With the PA turned all the way in the 24" shot a high of 653fps w/CPHP. 10 shot avg. 649fps.
Did the same after changing barrels, 18" " " " " 590fps " " " " " 582fps.
Your results may vary.
2250XE w/18" barrel
(http://i129.photobucket.com/albums/p212/wwk1a/2250XE/100_06101.jpg)
BillK mentioned my earlier test in .177 bulk-feed from a 12 ounce CO2 GMT with an 18" and 24" barrel. There seas a velocity drop with the 18" barrel, I don't have my chrony data handy but there was a velocity drop.
I've just built a new gun on the Disco tube and wanted to compare the 18" and 24" on bulk-fill. I lost almost 100 fps with the shorter barrel. 24" average 843, 18" average756.