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Air Gun Home Forum Index » Pellets/Ammo » High Velocity Pellets lose accuracy Goto page Previous  1, 2, 3, 4
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PostPosted: Sun Aug 15, 2010 8:38 pm Reply with quote
xanderman
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As per my last post, it is NOT over powering the bullet so that it "can't handle it", it is a matter of ballistics, air flow and supersonic stability as some others have mentioned.
The skirt is neccessary to maximize the efficiency, to catch the most air possible and prevent blow-by.
With a standard boat tail bullet there will be substantial power loss, either with blow by or with increased friction to prevent it, coupled with increased mass of the projectile the working speeds will be subsonic without doubt, unless...
Increasing barrel length while maintaining the clearances, allow a bit of blow by and keep friction down a bit, but the bullet will be in the barrel a bit longer and accelerated for a greater distance/time.
The problem with air guns is a lot of the energy is spent after the bullet already leaves, compressed air continues to escape witohut effect on ballistics, utilize this wasted energy by the longer barrel and it will compensate for the decreased efficiency with the missing skirt.
It will also be possible to use more powerful power plants, because it is presently limited by the time the pellet is in the barrel, longer stroke is ineffective! Shorter stroke is an attempt to compensate by more power faster, use it up before it is wasted on an empty barrel.
I'll try to build one this year and post specs here if anyone is interested.

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PostPosted: Sun Aug 15, 2010 8:52 pm Reply with quote
rsterne
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You seem to be talking about Springers because you are using the term "stroke".... If you read up on Springers, you will find that nearly all the velocity is attained in the first foot or so of barrel.... Longer barrels seldom give much, if any, additional velocity.... and in fact may be slower....

PCPs are a totally different animal.... and that is why they tend to be loud.... In virtually all of the high-powered PCPs, the longer the barrel the higher the velocity with a given pellet.... and this is especially true with the lighter pellets.... If you run across a "quiet" PCP (unshrouded) you will find that it is likely running high pressure and limited FPE.... The pellet is being propelled by a very short, sharp pulse of air (much like a springer).... and hence little air is being wasted....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
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.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Sun Aug 15, 2010 9:22 pm Reply with quote
xanderman
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rsterne wrote:
You seem to be talking about Springers because you are using the term "stroke".... If you read up on Springers, you will find that nearly all the velocity is attained in the first foot or so of barrel.... Longer barrels seldom give much, if any, additional velocity.... and in fact may be slower....

PCPs are a totally different animal.... and that is why they tend to be loud.... In virtually all of the high-powered PCPs, the longer the barrel the higher the velocity with a given pellet.... and this is especially true with the lighter pellets.... If you run across a "quiet" PCP (unshrouded) you will find that it is likely running high pressure and limited FPE.... The pellet is being propelled by a very short, sharp pulse of air (much like a springer).... and hence little air is being wasted....

Bob

Of course that could be changed by using a longer stroke in a springer which would continue to compress air to drive a bullet through a longer barrel, along with a slightly larger port to allow more air through and less compression, an earlier start so there is continuous acceleration throughout the barrel.

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PostPosted: Sun Aug 15, 2010 9:31 pm Reply with quote
rsterne
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I guess if you build it, we will see.... I suppose it's possible that current Springer design is flawed.... and that it is easy to get more power.... Rolling Eyes

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Sun Aug 15, 2010 11:27 pm Reply with quote
xanderman
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Maybe not flawed, exactly, but differing goals. They have to market to the general populace, so they have to make ammunition readily available, they couldn't market a rifle which will not fire standard ammunition and a rifle tuned to fire a 55 grain bullet is not going to last long when someone tries to put a 5.4 grain PBA pellet in it, talk aboutt he piston slamming hard!
Also, having a long stroke will have some interesting problems, like either a ridiculously long cocking levers and travel, or extremely high effort. Luckily I'm 270lbs with very good upper body strength, I plan on putting the cocking effort near 150lbs.
The biggest problem I'm going to run into is finding a long barrel, since I don't have a lathe...
I've only had a pellet rifle for a few weeks, so all my experience is coming from throwing javelin, shot-put and discus, as well as some physics, but the same sort of principles apply, the longer the force is applied the faster trhe projectile is going to go, flexibility is just as important as strength in throwing, as travel is just as important as the tension in a spring or the duration of an impulse to the pressure.
Since I've had my rifle I've cut the butt stock shorter, made a barrel sleeve/silencer to strengthen the barrel and lengthen it, and added a secondary spring with opposite twist inside the main spring and some modifications to the spring guides.
The most difficult part was drilling a barrel 18 inches long, had to actually make my own drill bit, welding and grinding to make a .480" bit 24" long including tang, if that's what it's called on a drill bit?
I've gained 250fps to make it supersonic with 11 grain pellets, more if there is any dieseling. It is terribly inaccurate but I don't mind playing with it since it was inaccurate and more importantly inconsistent before any modifications. (not user error, I competed in the national rifle competitions several times)

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PostPosted: Mon Aug 16, 2010 9:48 am Reply with quote
fritz
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Dead Horse

You're going to have to fire this creation from a bench vise. Really, having a barrel that long with an incredibly piston stroke will make it take ages for the pellet to leave the barrel. Due to the nature of springers and their hatred for sitting still, having the human involved in this would take much effort on your part to hold this behemoth still.

I wouldn't even consider a normal contour barrel, thicker the better. First because of the expected forces (150#) will likely bend a normal contour into spaghetti. Second, the extra weight will help absorb some energy during the firing cycle to slow down movements (aiding accuracy).

You may just be the reason a spinger in inaccurate. The shooter affects POI far more with his hold than he would using a HPA/CO2/PB. This is because of the firing cycle of springers. Google "artillery hold" for more information.

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testing pellets 
PostPosted: Mon Apr 25, 2011 1:30 am Reply with quote
KenMoran
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Try this for pellet testing,

Observing all safety precautions

Wait till late afternoon when the sky in light blueish, sun in your back.

Fire pellets a bit above the horizon and watch their flight.

Even through a scope you can see the pellet path, this can give a quick indication of whats going on with them.

I was having trouble with a .22 rimfire and Fiocchi low velocity rounds, the above test showed they were corkscrewing out of the barrel like crazy. I dont know if it is the gun or the projectile but they are very short in length, bought no more of them.
Longer projectiles didnt do it though.

Just a thought for you!

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PostPosted: Thu Oct 13, 2011 3:08 pm Reply with quote
viper2788
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AirGunEric wrote:
I think part of the problem with the "high velocity" pellets is that they are designed to try and eke out greater velocities than a "standard" pellet shot from the same gun (i.e. same power)- not shoot better from a gun designed for higher output/velocities. As noted in the article Westonhill linked- anything around the sound barrier requires the entire design of a diabolo pellet to be ignored and a "bullet" used. Problem of course is that a gun that will shoot a 10gr diabolo at 1100fps will only shoot a much heavier 30gr lead bullet at 400fps- doing all sorts of funky things with its trajectory and range.

The problem here seems to be quite simple- manufacturers are just starting to go too far in the "numbers" game. The bigger the number, the more guns/pellets/whatever they will sell- so now we have "high velocity pellets" for lower-powered airguns and "high velocity airguns" that can't shoot projectiles that would be appropriate at those speeds. Maybe if someone designs a 10gr bullet, that would satisfy the requirement- but with lead that may not be possible- once you fill in the skirt and waist to make a proper bullet-shape, its weight is going to go up significantly.


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High Velocity Pellets lose accuracy 
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