What determines the minum length of rifling needed to stabilize a 7.0 grain diabolo wad-cutter for precision & accuracy at 20 yards?
Length of rifling?
- Thread starter Troy Bakel
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Taken literally, your question reads a little bit like "what determines the number 5?"
The minimum length is whatever it is. Are you asking about the physics it takes to estimate that length?
There's a tonne of variables that go into it, like how tight the barrel fits the pellet, the type of rifling, twist rate, when the rifling starts, etc etc.
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Yes!
Exactly!
I have the equation that is actuality used to determine the required twist rate that includes all the variables for this pellet.
I have the internal ballistics curves to tune the rifle to efficiently launch this pellet.
What I don't have is an equation with all the variables that determine the minimum / optimal length of rifling required.
Do you know of such equation?
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A di
Refere to postings from @Ballisticboy.
I already have the twist rate required what I don't have is the optimal length of twist, is it 10 mm or 700 mm or something in between.
A diabolo pellet does not need spin to stabilize it, it will aerodynamically stabilize Itself. It needs spin (gyroscopic force) to lower the dispersion and make it more accurate and precise at a given distance.
Refere to postings from @Ballisticboy.
I already have the twist rate required what I don't have is the optimal length of twist, is it 10 mm or 700 mm or something in between.
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Not sure what your after,but there ,is no formula that gonna predict accuracy ,impact or if it’s in this zone of math ,it’s got to be right.. Especially with the mechanics of springers and the tuning. PCP might be more predictable.
As for correcting it self.
. Shoot on backwards. diablo Don’t mean they are cats. Smooth bore would be uselessUpvote 0
Stabilizing a diabolo has nothing to do with correcting its trajectory.Not sure what your after,but there ,is no formula that gonna predict accuracy ,impact or if it’s in this zone of math ,it’s got to be right.. Especially with the mechanics of springers and the tuning. PCP might be more predictable.
As for correcting it self.
Please refer to postings by @Ballisticboy .
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On the FX Royale platform, once a favorite & well represented gun at most competitions, only the last 3.5 or 4" are rifled. Original Smooth Twist barrels. Incredibly accurate pellet shooters!
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I think that your statement is completely true for round nose pellets. Wadcutters probably benefit from some spin because they have less mass at the front, and the air flow over the flat nose is less "friendly".
Even so, pellets benefit from some spin, to even out the effects of anomalies in the pellet, or nicks from shipping. A bit like drilling a barrel on a lathe helps make the hole travel true down the center; as proposed to spinning only the drill while holding the blank still. Ditto for the fletching on arrows being set at a slight angle to slowly spin it. It is to average out anomalies in flight, that would tend to cause the arrow to veer off to one side.
Too much spin with pellets is a bad thing, hence why the slow effective spin rate of the original FX smooth twist barrels worked well for long range shooting:
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I’m not aware of such equation. Nor have I seen it discussed. As mentioned above, there have been barrels with minimal length of rifling at the end of the barrel and they did ok.
In MOST cases, however, the rifling length is equal to the barrel length. The barrel length is determined by your internal ballistics needs to achieve a desired velocity. Meaning, 1” of rifling may be sufficient for spin but not for the velocity needed.
If you are thinking that it might be ‘slipping’ and needs time to ‘spin up’, that SHOULDN’T be the case. That would only indicate an ill fitting pellet.
Dave
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IZH used hammer forged Baikal barrels. The forging process for a barrel used in the Olympics and world competitions has 7 steps.
The most critical deminsion is the pellet to chamber fit. Pellets were custom made for each barrel used in world and Olympic competitions. The differential pressure developed across the pellet in the chamber when fired determines the acceleration rate and consistency of that rate.
The next critical dimension is the chamber to rifling transition point and finally the rifling itself which land to land was the same inside diameter as the maximum outside diameter of the pellet head and skirt of the custom pellet and the lands had rounded edges.
The length of rifling was 2% longer than the total distance required for the pellet to reach the desired velocity.
The next critical dimension of course is the rifling to bloop tube transition which is basically an internal crown. Bloop tube length was based on maximum site radius allowed by rules.
The rifle barrel ended up being nearly identical in internal dimensions as the pistol barrel but with a bloop tube.
Twist rates varied from 1:30" to 1:60".
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“The length of rifling was 2% longer than the total distance required for the pellet to reach the desired velocity.“
If I’m understanding correctly, if it takes 16.000” of barrel to achieve desired velocity, one would need to add 0.320” of barrel to have the proper length of rifling. ?
Dave
If I’m understanding correctly, if it takes 16.000” of barrel to achieve desired velocity, one would need to add 0.320” of barrel to have the proper length of rifling. ?
Dave
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These single stroke pneumatics are less than 6 joules muzzle energy with velocities less than 600 ft/sec. 16 inches of rifling is just drag after the pellet reaches 450 ft/sec in ~ 4 inches.
Olympic air pistols today do not have 16 inch barrels and their velocities are between 400 and 600 ft/sec.
Today's Olympic air rifles reach 835 fps.
Which is why I asked the question, do you really need nearly 3 times the rifling length to go from 596.4 fps (Olympic pistol) to 835 fps (Olympic rifle) a difference of only 238.6 fps.
The answer is no, it's just cheaper to rifle the entire barrel and batch test pellets to find those that are both accurate and precise for that barrel. That is why H&N offers 3 different diameters for their competition pellets and if you are good enough you can have your rifle tested and receive custom factory sorted MEISTERKLUGEN pellets that shoot the best from your rifle.
For non precision rifles that are required to shoot a variety of pellets and slugs at high plenum pressures and velocities I would go with the number 5.
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The 16” was only for an example to clarify if I understood correctly the rifling length relationship. Your response doesn’t clear that up any, only that we are only talking about Olympic guns apparently.
Dave
Dave
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I saw 5 pellet group testing results for both the Walther top level 10 meter air rifle and top level 10 meter pistol. Both were shot from a vice and both had the exact same group size at 10 meters. This led me to ask the question.
I knew a diabolo was self stabilizing and needs spin only to reduce dispersion.
I knew the 10 meter precision air rifle and pistol manufacturers are the only ones with major skin in the game in regards to off-hand precision airgun shooting.
So yes, I knew the answer would probably not come from AGN, I knew it would come from the 10 meter precision shooters.
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My question of my understanding the relationship has yet to be answered. That’s cool, I really don’t need a confirmation of the relationship as I’m not messing with Olympic style shooting.
Have fun with your project,
Dave
Have fun with your project,
Dave
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Some months ago I was told if an article tested accuracy of good barrels and changing lengths of said barrels. Their findings were that an accurate barrel and it's accompanying twist rate remain constant no matter the length, and length of barrel only effected speeds and not accuracy.
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