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PostPosted: Fri Mar 13, 2015 12:28 am 
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Joined: Sat Mar 16, 2013 5:15 am
Posts: 3406
Location: Edmonton
RC wrote:
How about this one....

Watched Star Wars last night and listened to Master Yoda. Just came back from the range and used a sub 500 fps break barrel, no sights, unsorted CP 7.9gr pellets and blind folded shooting at 100 yards.... 10 shot group! Scouts Honour... :butthead:

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Believable... if the Force was with you.


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PostPosted: Fri Mar 13, 2015 12:37 am 
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Location: Edmonton
calico wrote:
Hi guys,
Introduce my name is Ruddy, I'm from the other side of the planet, jakarta-INDONESIA.

The reason I post this questions are:
1. Nobody post this .177 with serious airgun and mod built for this long range.
2. There should be somebody taking this seriously with benchrest, long barrel, right pellet speed, selective pellet, etc. and I want to see it, don't you?
3. I use HW100 with Walther barrel 70 cm long without choke, JSB heavy pellet, 1000fps and never get the grouping I want, so far it's about 5 inch grouping at 100 yards.
I believe there will be alot to discuss how to modify the airgun to reach the smallest grouping.
Have not try to reduce to 850fps. Not yet.
4. .177 require no permit, higher than .177 does, I have no choice but us .177.
5. Getting the permit here is complicated, time, birocracy and money.
6. I believe Somebody should do better grouping than Ted holdover on youtube
https://www.youtube.com/watch?v=QFou_4VqLBY

If you can get grouping with in a dime, you should make a nice documentation like airgun you use, pellet brand, pellet speed, any modyfication you 've made, etc.
And please don't tell me you can shot that range without scope? At a dime grouping ???

In my country the law is odd.
Higher than .177 required permit, so .177 require no permit!
And I can use .177 2000fps or higher without breaking the law.
I hope there is somebody would like to share and discuss.

Btw, i can not believe a dime grouping ???
Proof it it's real by making a new documentation like video .
Are you saying better than ted holdover on youtube?
It's what I want to proof that somebody can do this actually.


You see, you're just not supporting your hypothesis with anything even possibly credible. Now, you're shooting .177 at 2000 fps. Didn't you know that .177 pellets hit sound barrier velocities at 1000-1300 fps and then fragalate into a lavender-scented powder at approximately 1560 fps?


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PostPosted: Fri Mar 13, 2015 5:36 am 
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Location: Central West River Nova Scotia
He didn't say he was shooting at 2000 fps. He said that by the laws of his country, he can legally shoot any speed with a .177 cal. 2000 fps was arbitrary to demonstrate the way the laws are set.
I have a 100 yd range and have an AT44 .177 and could not get better than a 5 inch group. however I have not had a completely windless day to seriously shoot and record at that range.
My .22 cal sumatra will hit a golf ball at 100 yds avg 1 out of 3 shots, with the other 2 shots only a pellet width away, so under 2 inches. but again. where I live there seems to always be a breeze during the day. Right before sun up and after sun set, the wind dies completely, but shooting in the diminished light at 100 yds is impractical.

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If I had only one wish, it would be to be able to "unsay" things.


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PostPosted: Fri Mar 13, 2015 11:59 am 
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Joined: Wed Jan 05, 2011 12:35 pm
Posts: 5791
Location: P.G. B.C.
Try for 900fps to 960fps with a 10.5gr. (HEAVIER) match pellets - that was a magic combination in my .177 PCP rifle - but - I never shot it at 100 yards - it did, however give me many groups at 25 yards, that were in the 0's and 1's. That is, it made 5-shot groups from .050" to .150" at 25 yards, the greatest distance at which I shot it.

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Daryl

Air Force Condor .25
Umarex Gauntlet .22
Air Force Talon .177
HW97 KT .177
HW98 .22
Brocock Concept .22
Artemis PP700S-A Reg. .22
Artemis PP800 Rebel Reg. .22


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PostPosted: Fri Mar 13, 2015 12:56 pm 
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I think this raises some really interesting questions. We know that PBs can shoot .17* accurately at high velocities - look at Daryl's targets on page1. Presumably it can be done because the bullet stays at supersonic speeds for the entire flight, and the design of the bullet is stable at those speeds. So, what's the lowest (supersonic) speed that accuracy is maintained at? What's the lightest bullet that it can be done with? Those two would tell us how much energy we'd need to be able to get into that regime (supersonic flight out to a 100 yd target), and then the question would be, is that possible to build in an air gun? Bob has managed, what, something over 500 fpe in large bores? It's hard to get that much power behind a .177, but I wonder what is achievable. Just ball parking it, if we wanted 1500 fps with say an 18 gr load, that works out to 90 ft/lbs at the target. It sounds difficult, but maybe possible? I'm imagining a very long barrel, with the TP outside the barrel so that the TP bore could be >= barrel bore without loading problems (something like the IZH46M layout), and high pressures. What else would factor in?

Jim

[Edit] I found this link recounting how Dennis Quackenbush built a rifle in .25 caliber and .375 caliber and used light weight delrin pellets, but still topped out under 1500 fps:
http://www.pyramydair.com/article/How_f ... ch_2009/59

Maybe there's some fundamental physics going on that makes it difficult to top that? Expansion of a gas wave front in the barrel at supersonic speeds maybe? Speed of sound increases with pressure, but during the shot barrel pressure falls rapidly.


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PostPosted: Fri Mar 13, 2015 2:03 pm 
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Posts: 2514
Location: Vancouver
Bob Sterne would no doubt have perfectly simple math to support an explanation of why a PCP isn't going to do what a powderburner will do. But my take on it without the math is that the pressures are about an order of magnitude lower with even the most powerful PCP. An exploding powder charge in something like a .17" HMR generates something in excess of 50,000psi at the muzzle. Obviously even with a 5,000psi PCP, you're still looking at a maximum pressure at the muzzle, on the first shot, of 5,000psi, that's if this magical, imaginary PCP were 100% efficient. And your second shot would be slower unless tethered to a very large tank. Add in the fact that the valve dump from a PCP primarily gets the pellet moving, with the expanding air volume dropping in pressure behind the pellet quite early in the travel down the bore, and you're probably looking at closer to 2,000psi or lower at the muzzle. There's no way that's going to push a pellet anywhere near as fast as a high powered rifle round.

But I suspect that using a custom boat-tail bullet instead of a pellet and firing that at over 1,500fps might prove stable enough out of a PCP, so long as it hit the target well above the speed of sound, so staying about 1,200fps at 100 metres. You'd also have to have a very stable barrel and the right rifling and twist rate and sufficient but not excessive (too much friction for a PCP when you go above ~24" or so) barrel length.

I wouldn't want the job of casting hundreds or thousands of precise bullets for such an application. Doesn't sound like fun, but there are no doubt guys who see it differently. So if I were going to shoot 100 metre competitions I'd probably build something with a 24" LW or FX Smoothtwist barrel and figure out the pressure and dump volume to get the heaviest JSB field target pellet moving at around 900fps. The trans-sonic instability problem is just too messy to flirt with so keeping it well under 1,000fps is better in case of very cold days when the speed of sound gets a lot closer to that velocity. And as PCP efficiency apparently drops dramatically when pushing past the mid-800's (from stuff I've read in various of rsterne's and other guys' comments), it seems a better idea to stay around 900fps or slightly lower.


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PostPosted: Fri Mar 13, 2015 2:21 pm 
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Location: Coalmont BC
There are a few things going on that make it extremely difficult to achieve supersonic velocities, particularly at the target, with an airgun....

Internally, while accelerating the pellet, you have to deal with the speed of sound in the compressed air, which although it does increase somewhat at very high pressures (at 4500 psi, it is ~ 1550 fps), when the airflow reaches Mach 1 (at that temperature and pressure) you reach a mass flow limit, beyond which you can't cram more air down the pipe.... In addition, the air molecules themselves have an average velocity of about 1650 fps, which imposes somewhat of another limit.... So, unless you change over to Helium, which has a higher speed of sound, and higher molecular velocities, those limits impose huge inefficiencies before they are even reached.... You can push the velocities supersonic with a PCP, but only at the cost of HUGE air use.... In addition, as you increase the Sectional Density (weight) of a bullet, you need to increase the pressure and/or barrel length to achieve those high velocities....

Externally, any object approaching the speed of sound sees a huge increase in drag, which even has a name, the "Drag Discontinuity Mach Number".... It occurs, depending on the shape of the object, between Mach 0.6-0.9, and the drag increases by a factor of three to five times between subsonic velocities and supersonic velocities.... If you launch a diabolo pellet at 1300 fps, it has so much drag it drops below the speed of sound in about the first 10 yards.... Yes, by changing to a much heavier and better streamlined bullet you can delay that velocity decay, but then you need a lot more energy to accelerate that heavier projectile supersonic in the first place.... meaning more pressure and/or barrel length.... Even a .22LR high velocity bullet, starting at about 1250 fps, drops subsonic by about 75 yards downrange....

The combination of these factors means that for airguns to have any reasonable efficiency you have to keep the velocity below the point where drag skyrockets (typically in the mid 900s)....

Bob

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