increasing shroud volume
Has anyone ever machined down the diameter of the lothar barrels from factory? The reason i ask is i have pulled the barrel out of my standard .22 condor and was quite taken by how heavy the barrel actualy was. We have much much lower pressures than a powder burner, just curious why we need such meaty barrels? Would it be possible to turn down the barrel to a smaller diameter say standard is 16mm so the wall thickness of a standard barrel is around 5 mm, could that be reduced to 3mm or less?
The idea being 1) it would make for a lighter gun overall, and 2) would allow more volume in the shroud frame area. Any thoughts?
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Hi guys , and thanks for the messages. I must apologize for the delay in getting back to you guys. I have actualy done some work on the Condor. Ive machined down an 18″ .177 barrel i had to 10mm. Ive machined a combination barrel bush shroud that holds the shroud in place around the barrel. The front barrel cone thing then holds the shroud straight.. ( I hope) ! I havent finished the project yet, as i still need to machine an end cap for the shroud. The shroud continues past the barrel a further 6″ inches or so. I wont really know what effect turning down the barrel will have on accuracy till i shoot it.
But further to the points you guys have raised about frequency of barrels, i dont mean any offence, but i am sure frequency or the vibration on the barrel comes from the massive amount of pressure when a powder burner is fired. This is somewhere in the vicinity of 30,000 psi not 3000 psi. Also what accures when a rifle or shotgun is fired, is the pressure behind the bullet or shot charge expands the barrel quite significantly. Especially in a shotgun a ripple or bulge travels down the length of the barrel and i that is what causes the harmonic frequency or vibration in a barrel. The harmonics or vibration are not a bad thing as all powder barrels do it, but if a barrel vibrates a certian way ie to the left then as long is it continues to vibrate at the same pitch or frequency, then it theoretically should shoot in the same place.
Of course i take into account everything you guys have said, and i hope this damm works, cause it looks pretty damm good if i do say so myself ! And more importantly it could pass off as the barrell ! I have promised photo’s and as soon as i get the time to strip it down and take some pics i will, just been pretty hectic at work for a few weeks. Ill post again as soon as possible.
Another good example of barrel frequency and accuracy is the Mini-14, they are just not tack drivers. But when Ruger added a heavier barrel and a muzzle weight that was adjustable, the same old action suddenly became a target gun. Usually, the more mass you add to a barrel, the slower the flex and oscillation, and the more time a pellet/bullet has to exit smoothly on it’s way. The other issue is predicting the effect. The fewer the points of movement, the less random the product. Then add increasing velocity and friction, and optimal pellet/bullet to barrel contact, and muzzle crown angles and uniformity, and on and on.
My Talon is a tack driver and messing with it will likely change that to a semi-tack driver…. 🙄
Thanks Scott.
muzza, no offense taken. If you find a way to make it work, more power to you. However, your comments make it clear you probably have a couple things you may want to look in to. First of all, you are mixing apples and oranges. FLEX is not the same thing as OSCILLATION or resonant frequency. Flex simply is how stiff something is when you push against it, or “loading” it by applying pressure on one side of it and seeing how far it moves without breaking or permanently deforming. Oscillation is the thing moving on its own after a shock is applied to it, picture a tuning fork. You bang it against something to get it going; then it rapidly wobbles to and fro. The frequency, or how fast it wobbles, is its resonant frequency.
all things vibrate, some are just faster or slower than others. Things that greatlly affect oscillation frequency are stiffness and mass. By machining a barrel down, you are changing both. by changing where it touches, or anchors, to the chassis you are also changing frequency. And yes, airgun barrels do oscillate, just like powder guns.
I guess the easiest way to learn the hard way is by watching a slow mo video of the AK47. It was quite an eye opener for me. When the US got its hands on some of the first models and ran tests on it, the GIs complained that they couldn’t hit shit with it because the damn things were so flimsy, they were flexing all over the place. Now, you may think that metal is stiff and strong and how the hell could it flex enough to move a bullet impact?
http://ammosmith.com/forum/rifle-reloading/barrel-flex-in-an-ak-47-slo-mo/
(the video near the bottom of this page)
What is happening is that all of these things happen within a time frame that has little to do with the vast majority of human experience. what this means is, you can’t detect these types of events directly. You can only see them using machines to slow the event down to where you can see them. And when you do, they are an eye opener. But you CAN observe the effects, i.e., changes in accuracy, directly without machines and use that as a defacto alternate gauge of oscillation freq and/or stiffness. The thing to take away from this is, just because you can’t see them, doesn’t mean you can ignore them. Understanding them helps, especially with tryiing to solve the problems they create.
For instance, I’ve read that simply attaching a weight, such as a suppressor, to the end of the AK47 barrel will improve its accuracy TREMENDOUSLY, make it shoot about as accurately as an AR15. I have no first hand experience with this, but the author of the article is someone I greatly respect, so I have no reason to doubt any of it. It also makes sense, from a physics point of view, since you are increasing the mass of the barrel at its very end, where the addition of mass has the greatest effect on oscillation frequency, the farthest out from the anchor point, or moment arm.
Again, good luck on your project. I hope it panned out well for you.
aloha,
walt
Like Samsterii said.
I’m used to have one in the Condor, with just 5 front chambers made from cork (including the washers)Not heavy at all…..Extremely quiet…just can hear the sound of the hammer.
Greetings from Argentina
Juan Martin
A 20mm shroud will need volume length-wise and some pretty aggressive air diversion (creating massive turbulance) but it will work better than nothing at all. I noticed that lots of washers in the shroud is popular with little spaces inbetween them. That adds a lot of weight and I don’t think it helps that much. I saw a pic online of the Marauder shroud and it only has like four air chambers, narrow but long. And no fancy formed discs etc. They say it’s quiet…. Sounds like you are making something similar.
listen to Walt…. he knows his shit!
I think this is how most questions get answered here. Someone trys it and sees how it works and passes it along. Then someone comes up with abetter idea and tests that. I find that cool as hell! Thats how we ended up with pellet guns that shoot 100 yards! (accurately)
Pushing the limits teaches us the real limit, not the calculated limit.
No one is dying here may turn a barrel too far and looses accuracy.
Lesson learne how far we can and cannot turn them down. 💡
Hi Guys, thanks for the posts. I have been busy playing around with a .177 barrel i had made from an old Gamo break barrel. The results are encouraging. No Offence Walt but we are talking about an air rifle, not a powder burner. There is no explosion and subsequent barrel bulge upon firing an air rifle. I may be wrong, please correct me if so, but i dont think flexing would be a problem. I have machined down a .177 barrel to 10mm, which gives it a little over 2.5mm wall thickness. The barrel is still incrediblely stiff and would require quite a knock to bend it. I have used a 20mm Aluminium tube as a shroud. I machined a barrel bushing that fits the 20mm tube and sits over the barrel. I will post some pics shortly. I havent had the time to do any accuracy tests, but will keep you guys informed of my progress. My only concern is that the 20mm shroud may not be enough to queiten the report. I guess there is only one way to find out !
I noticed the Talon is not balanced at all and the tank end is heavy. Lightening the barrel more would not benefit you much at all. A long Condor barrel turned down in the rear might be a thought but I wouldn’t do it.
i would be worried about the barrel flex and possible loss of accuracy
stresses probably aren’t the issue. Harmonics is. When you reduce the thickness, you change the resonant freq of that barrel. There are equations to predict the resonant freq given the dimensions but I’ve always placed more stock in what a barrel does than what my computer model says it should do. Roundabout way of saying your best bet is to cut one and try it out.
Rule of thumb, the thicker and heavier, the slower the harmonic freq so the easier it is to control. But on a 24″ bbl I don’t feel comfortable reducing the diam by very much more than the existing .630″ On a .22 I could see going down to around .500″ but probably not that small on a .25
walt
Pcp air rifles suffer the opposite of warm barrels….
I agree there isn’t much heat compared to a powderburner, although the pellets ripping down the barrel under pressure and friction still creates enough heat to move point of impact a little. I shoot weekly smallbore matches and my cold shot is always off from the warm groups just enough, and my barrel is .920″.
It would be interesting to find out just how much heat is created by a pcp gun. And then there’s the cooling effect of the air released. Considering it’s cold air should neutralize the heat from friction some. Now I have no idea!
As for “floating barrel”, the Airforce models use the bushings and there’s contact with the shroud right? Then they aren’t floating. If you really wanted to get crazy, machine some bushings with O-ring grooves on the outer diameter so they absorb some harmonics and isolate the barrel from the shroud some. Might really help a thin barrel, but the heavy ones might not notice an improvement. The threaded bushing idea and hiding a longer shroud idea gets my gears turning!
The 12 inch barrels are thinner, if you can turn the 24’s down without stressing them, you could go to the same diamater as the 12″ers and use those bushings.
Heat is not a factor and air gun barrels are not as hard.
RC
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And a tuning fork is a powder burner? I wonder how it vibrates (thats simple speak for frequency oscillation). The AF guns are so light up front that tuning down a barrel is a little silly IMHO. I’d rather have one about .920″ on the last 4″ of barrel. I think the world shooting community is on one side vs the other in spades….. 🙄