|
|
Post by snyper on Nov 26, 2008 8:04:45 GMT 8
HOW BARREL LENGHT AFFECTS VELOCITY IN A PNEUMATIC AIRGUN
by
B.B. Pelletier I didn't intend for this to become a series, but the comments to the first post about CO2 guns requested this post. Okay, I offered it at the end of that first post, so I guess I wanted to do this one, as well. I was really surprised by the results of that CO2 barrel length report - they weren't what I expected at all. When I thought about it, the reason I said that I thought a 24" barrel on the Crosman 2250 would increase velocity by 100 f.p.s. is because most of my experience has been with air, where there really is a dramatic difference like that! Today, I will make the case that increasing barrel length in a pneumatic gun readily increases velocity. Airguns of the past had longer barrels!My first piece of evidence comes from the past. All the big bore airguns of old had long barrels, and the reason they did was for velocity. Those old guns (and I am including the few rifles among the guns) operated on air pressures of 500 to perhaps as much as 900 psi, though I suspect that last pressure to be a bit high. Most of them were comfortable with 600-700 psi. We know this for a fact because Dennis Quackenbush and Tom Gaylord did a study of vintage pump designs and determined their limits. They demonstrated that a single-stage hand pump can generate up to 1,275 psi if the person doing the pumping is heavy enough and the pump piston is small enough. They also found a practical limit for the old pumps, which actually delivered around 800 psi, give or take. Their study is published in Airgun Revue 4. The ONLY way to generate higher velocity with pressures that low is with a longer barrel. Indeed, when we measure the length of vintage big bore airguns, they have barrels that range in lengths from 28 to 33 inches. There are guns with longer barrels, but there aren't many with shorter barrels (except for handguns and guns made for children). The locks on the old guns held the valves open much longer than contemporary airgun valves. An examination of the vintage valves reveals huge air passageways! Everything was designed to move large volumes of air. It takes a long barrel to take advantage of that. If you're interested in how these old guns operate, check out the DVD Antique Bigbore Airguns - From Novelty to Necessity. A more elegant proofProof No. 2 is a remarkable air rifle that has stunned the world! The USFT rifle produced by Mac-1 Airgun delivers 55 shots of a 10.6-grain Beeman Kodiak pellet traveling at 900 f.p.s., and it does it on a starting air pressure of just 1600 psi! When the string is completed, the gun will still have 1100-1200 psi remaining, so all that work is done on as little as 400 psi of air. The air reservoir of the rifle is HUGE! Although the air PRESSURE is relatively low, the VOLUME is very great. Obviously, when a given volume of air is made smaller without air loss, the pressure increases. The USFT rifle reverses what most modern PCPs do. It uses a larger reservoir to lower the pressure of the air. Same amount of air - bigger volume. The ONLY way to use this lower-pressure air effectively is with a longer barrel. When the pellet leaves the barrel, the push provided by the air stops. The USFT rifle uses a 25" Weihrauch barrel, which is the longest one they make. If they offered a 28" barrel, I have no doubt it would be incorporated into the USFT - not to increase the velocity, but to lower the air pressure needed to achieve 900 f.p.s. By the way, this rifle starts at $1,650 and goes up rapidly past $2,000 (and Mac-1 is backordered for several months from the demand). Top competitors are switching over to this purpose-built field target rifle, and they all agree that 900 f.p.s. is the ideal velocity, when accuracy is on the line. This gun just took four of the top five places at the U.S. Nationals, including first place. The final proofThe final proof is so positive that there is no way to refute it. The .22 caliber AirForce Talon SS gets 820-850 f.p.s. muzzle velocity with a Crosman Premier pellet. It has a 12" Lothar Walther barrel. When you substitute a 24" Lothar Walther .22 caliber barrel, that SAME GUN jumps to 1,000 f.p.s or a little more. That's pretty amazing, but it doesn't end there. Because the Premier is going too fast for good accuracy in the longer barrel, loading a 20.5-grain Beeman Kodiak will slow down the speed to 920-950 f.p.s., but the ENERGY increases from about 32 to over 40 foot-pounds. And, a 28-grain Eun Jin will take the energy up to 45 foot-pounds with a velocity of 850 f.p.s.! The basic rifle with its shorter barrel was getting about 23 foot pounds from the Premier! You cannot keep extending the barrel forever. There is a turnaround at some point, and it will relate to the caliber of the pellet. A smaller pellet equals a shorter optimum barrel length. But air being so much thinner than CO2, this turnaround point will be much farther from the breech than what we saw in the CO2 test. To the best of my knowledge, this has never been thoroughly tested. If it has, I don't know where to find the results. This Article is qouted from Pyramid Air blog |
|
|
|
Post by snyper on Nov 26, 2008 8:14:56 GMT 8
HOW BARREL LENGTH AFFECTS VELOCITY IN A CO2 RIFLE
by
B.B. Pelletier 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 gunThe 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 testThe 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. This Article is qouted from Pyramid Air blog |
|
|
|
Post by hunterx on Apr 5, 2009 19:42:51 GMT 8
hi bro's i have a question in co2 ag barrel length..do you think the 24" long barrel will outshoot the short one which is 17" in terms of distance.kasi i noticed many hunters use longer barrel in hunt. in above post by snyper,the longer barrel has low in velocity which means hindi sya aabot long distance compare to shorter one's??tama ba mga bro?pls enlighten me on this one.tiy  |
|
|
|
Post by snyper on Apr 5, 2009 21:14:32 GMT 8
Bro based on the article on CO2, the most ideal barrel length for CO2 is about 19". But to answer to question. If you make an experiment of placing the barrel (gun) at a 45 degree angle, with the muzzle of both guns (with the 24" and 17" barrel) at the same level, then shoot a pellet with the same weight and FPS. Both pellets will land at the same distance.
If you move the barrel and align them at the breech, the distance of the impact point will have a very small difference, say about 4"-7". I think mathematics can actually be used to explain that, which I am no good at. hahahaha!
Hope that enlightens you. Cheers!
|
|
|
|
Post by hunterx on Apr 5, 2009 21:31:27 GMT 8
ty for explaining bro...hehehe |
|
|
|
Post by heightaddict on Apr 7, 2009 12:15:53 GMT 8
hunterx
with regards to co2, barrel length is important.
its how much co2 your dumping, the longer the better. the longer the barrel, the more you get (power) from expanding gas (co2).
question: would you want to carry a 30" barrel rifle? or would you rather have a 19" or 20" barrel rifle?
in that case, mods are important. its like getting the best out of your rifle. too short the barrel, you don't get enuf power from your co2, too long, friction come in and muzzle velocity goes down.
you can only measure speed or muzzle velocity using a chrono...you will find answers that way.
hope this helps
|
|
cobra
Full Member
Posts: 105
|
Post by cobra on Apr 8, 2009 21:00:12 GMT 8
Bro. Heightaddict,
Anybody you know makes 30" barrels? If there is, maybe we can do the theory into practice.
But the cost of a 30" barrel is expensive to manufacture just to increase the velocity of the pellet to an additional 300fps, I would prefer the 19" or 20" barrel that gets the velocity to more or less to 600fps.
|
|
|
|
Post by snyper on Apr 8, 2009 22:51:12 GMT 8
bro cobra, my good old armscor averages about 650FPS with its 19" barrel. If 600 is your target FPS then that is very easy to do.
Just my two cents. Cheers!
|
|
cobra
Full Member
Posts: 105
|
Post by cobra on Apr 9, 2009 1:15:59 GMT 8
Bro. Snyper
This also depends on the weight of the pellet since the power we get is based on the mass of the pellet times the average velocity.
Let's say the CO2 can produces a constant power so any change in the mass of the pellet will decrease the velocity if the mass is heavy or velocity is higher when you use a lighter pellet. So if you also test the air gun during the cold weather. So many variables are there such as temperature of the test area, the weight of the pellet, the coefficient of friction of the barrel against the pellet, volume of CO2 release, pressure of the CO2, air resistance, and ideal rifling twist
It is only a theory if I would prefer an airgun with a 600FPS in 19" or 20" than a 30" barrel where the volume and pressure of CO2 needs to be tested to give the maximum velocity.
This is what I want to say
|
|
|
|
Post by hunterx on Apr 9, 2009 18:29:14 GMT 8
bro height
tnx for ur advice. I will try the soft chrono i found in another thread. ty
|
|
|
|
Post by heightaddict on Apr 13, 2009 9:34:51 GMT 8
Bro. Heightaddict, Anybody you know makes 30" barrels? If there is, maybe we can do the theory into practice. But the cost of a 30" barrel is expensive to manufacture just to increase the velocity of the pellet to an additional 300fps, I would prefer the 19" or 20" barrel that gets the velocity to more or less to 600fps. its been practiced way back. early airgunners thought longer barrels will outshoot the shorter versions. that is why old airguns like the footpumps have long barrels. cebu have 24" barrels, ive seen 30" barrels in iloilo and of course some pictures of long barrels from laguna to pampangga. my old co2 bulpup clocked 740fps, the highest i got is 770fps. with a 19" cebu steel barrel. sold it for 12k....got me a pcp photobucket not working...will post the pics later  |
|
|
|
Post by BroJames on Jul 7, 2009 14:43:04 GMT 8
hi bro's i have a question in co2 ag barrel length..do you think the 24" long barrel will outshoot the short one which is 17" in terms of distance.kasi i noticed many hunters use longer barrel in hunt. in above post by snyper,the longer barrel has low in velocity which means hindi sya aabot long distance compare to shorter one's??tama ba mga bro?pls enlighten me on this one.tiy My belief is that it depends on the valve opening and how long it stays open. hunterx with regards to co2, barrel length is important. its how much co2 your dumping, the longer the better. the longer the barrel, the more you get (power) from expanding gas (co2). question: would you want to carry a 30" barrel rifle? or would you rather have a 19" or 20" barrel rifle? in that case, mods are important. its like getting the best out of your rifle. too short the barrel, you don't get enuf power from your co2, too long, friction come in and muzzle velocity goes down. you can only measure speed or muzzle velocity using a chrono...you will find answers that way. hope this helps Yes, that is what is impressed upon me by experts but I am not sure how much of that holds water. That in CO2 airguns, barrel length is important. I think it is because CO2 and the gas used in airsoft are refrigerants and somewhere in the conversion from liquid to gas, there is always some extra air or gas for a longer barrel to take advantage of. Of course, the valve also plays an important role. It was also impressed upon me (by experts) that in PCP airguns barrel length is not as important (or by not much). I am thinking that is because PCP is compressed air where it simply expands when released though the valve. PCP valve must be (or is) more efficient and longer barrels have not much extra air to take advantage of. I came from an airsoft background where longer barrels must be accompanied by longer cylinders (based on ports or openings on the side). The more popular airsoft guns are essentially spring-pistons where the spring is either pulled by battery-operated gears or by hand. In either case, they use air as powerplant. In gas guns this also appears true as I used to own a Kuan Ju Mark 2 carbine with extended barrel. In the case of this carbine, we have to increase the size of the valve openings (we call it a high-flow valve). If tank pressure is increased (the use of stronger gas), a stronger hammer spring is also necessary to push the valve open - and stay open longer. In some cases, the valve spring must also be stronger. Here, we see a lot of balancing required. Gas guns have refrigerants as powerplant and CO2 is also a refrigerant. In fact, an increasing number of airsoft gas guns in the market today have CO2 versions. My theory is that those who suggested that CO2 airguns does not benefit from longer barrels may have based their assumptions on their observation of non-optimized CO2 airguns. I have observed that Armscor airguns firing more than 20 shots on a single fill while some custom CO2 airguns can manage only 7-9 shots. Both having the same velocity. Conversely, those who suggested that PCPs does not benefit from longer barrels may have based it on their observation or the observation of others who conducted tests on airguns optimized for a particular barrel length. In airsoft, we call this air volume balancing. However, precompressed air (PCP) may be a different matter (from air pushed out by a piston). Maybe someone can elaborate on this. In the case of the crosman airgun it seems that crosman, having a ready "the barrel on the 2250 was optimum for that airgun.
" answer, are quire sure that their airgun is optimized for 24" barrels. In the case of the Quackenbush XL, Dennis Quackenbush and his father, were known for producing expensive reproductions and mostly caliber .30-.50 big bore airguns. It is likely that the XL was optimized for 20" barrels although the 18-19" seems better. But then, they may be just regular production variance. Bro. Heightaddict, Anybody you know makes 30" barrels? If there is, maybe we can do the theory into practice. But the cost of a 30" barrel is expensive to manufacture just to increase the velocity of the pellet to an additional 300fps, I would prefer the 19" or 20" barrel that gets the velocity to more or less to 600fps. Sir cobra, I believe I read somewhere that you also do some machining? Based on airsoft prices, a custom barrel measuring 15" is about P1500. A 17" around P1600. Butthe price of a 19" jumps to P2600. My wild guess is that a 30" barrel, if it can be customized locally, will cost something like P5,000-8,000. So yes, it can be expensive. 600FPS is actually powerful enough for most uses. But if I can get 900FPS with a longer P3,000-5,000 barrel alone it may be worth it. But that's gonna be a long f feet or so rifle. If you would like to conduct such or other tests, naybe we can try something out. bro cobra, my good old armscor averages about 650FPS with its 19" barrel. If 600 is your target FPS then that is very easy to do. Just my two cents. Cheers! Sir snyper, is that a .177? Bro. Snyper This also depends on the weight of the pellet since the power we get is based on the mass of the pellet times the average velocity. Let's say the CO2 can produces a constant power so any change in the mass of the pellet will decrease the velocity if the mass is heavy or velocity is higher when you use a lighter pellet. So if you also test the air gun during the cold weather. So many variables are there such as temperature of the test area, the weight of the pellet, the coefficient of friction of the barrel against the pellet, volume of CO2 release, pressure of the CO2, air resistance, and ideal rifling twist It is only a theory if I would prefer an airgun with a 600FPS in 19" or 20" than a 30" barrel where the volume and pressure of CO2 needs to be tested to give the maximum velocity. This is what I want to say I believe armscors, is limited by law, to 550FPS stock although there are people who "powerize" them for P1-2,000 (I think). Bro. Heightaddict, Anybody you know makes 30" barrels? If there is, maybe we can do the theory into practice. But the cost of a 30" barrel is expensive to manufacture just to increase the velocity of the pellet to an additional 300fps, I would prefer the 19" or 20" barrel that gets the velocity to more or less to 600fps. its been practiced way back. early airgunners thought longer barrels will outshoot the shorter versions. that is why old airguns like the footpumps have long barrels. cebu have 24" barrels, ive seen 30" barrels in iloilo and of course some pictures of long barrels from laguna to pampangga. my old co2 bulpup clocked 740fps, the highest i got is 770fps. with a 19" cebu steel barrel. sold it for 12k....got me a pcp x x x I have customers from the bicol area who have been hunters since childhood and they can really pump the footpump airgun. They were looking for 24" barrel footpumps and claimed that, from their personal experience, these (now hard to find) longer barreled airguns are indeed more powerful and has more range. Can you get closeup pictures of these long rifles? Eto na naman ako. Are there 24-30" footpumps still for sale? I am interested. |
|
|
|
Post by snyper on Feb 5, 2010 11:03:37 GMT 8
Stumbled on this one from the yellow forums: The Thread was titled What is the most efficient barrel length[/b] This is what Tim Mcmurray has to say: Original thread can be found here LINK |
|
cobra
Full Member
Posts: 105
|
Post by cobra on Feb 9, 2010 1:46:35 GMT 8
To finally put to light the most efficient barrel length we have to control the following:
1. the barrels should come from same manufacturer and materials.
2. temperatue at the time of the test should be same for the different barrel length
3. the air pressure should be the same at the time of the test
4. pellet weight should be the same
5. same air volume of the test
6. release valve hole is same
I think these parameters affect the results of the test.
I would like clarify that maximum velocity you can get from the different AG manufacturers was based on their experiences and own tests not from laboratory controlled experiments.
|
|
