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Old 05-28-2013, 03:37 PM   #1 (permalink)
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When do FSR begin their rotation?

After spending some time on several FSR related forums I have yet to have the above mentioned question asked. Really, when do FSR's begin their rotation?

I fully expect some of the true paintball snipers to chime in and offer their two cents on the subject. Logic dictates that a super tight inner diameter would effectively eliminate any voluntary rotation until after the round leaves the barrel a'la Lapco's tight 68.3 FSR barrel. This theory of course goes out the window with a forced rotation barrel such as the HH series. It would stand to reason that an under bored rifled barrel might force the rotation to match the barrels spin not the FSR fins.

So now let's think about medium to over bored ID's and the point of my experiment.

For months I have been pestering Bill to create rifled shells. I even went so far as to contact HH in attempt to introduce CCM and HH for my own selfish reason of acquiring a rifled shell. Unfortunatly, the good folks at HH, are very busy and as far as I know they never followed through.

Still wanting to venture down this avenue, I decided I would do my best to determine when the rotation starts in order to better understand the charictoristics of the FSR fin. When viewed it appears as if the equator of the FSR is larger than the fin, thus causing people to believe the fins do not make contact with the ID, makes sense.

However after conducting a very rudimentary test I have a difference of opinion. I believe that although the equators OD is larger, the immediate force of the gas used to propel the round comes out so fast and explosive that the fin actually expands, similar to an umbrella opening.

Parameters:

CCM SR-1
CCM fluted stock smooth bore barrel.
FSR rounds
Baby powder attempted two applications.

Application 1) FSR placed in baggy, powder mixed in and shaken until coated.

Result: Failure, resaon not enough residue to see any markings.

Application 2) Pour powder directly down the muzzle.

Result: Success on two fronts. Success 1, striations left in both the CCM shell and barrel. These markings helped me to resolve the age old question of when does the FSR begin rotation.



You be the judge, do you see any unnatural diagonal markings in the shell? Note shells were loaded with round at the base of the shell not up front like a bullet.



Although difficult to detect, by now you have noticed diagonal markings on the ID of both the CCM SR-1 shell and 68.6 oversized barrel.

As promised, there was a second result of pouring the powder directly down the barrel. Something that might peak a would be snipers interest. The sound signature was significantly reduced, maybe even better tan an after market silencer. Not to mention the poof of powder really added some realism to the whole test.

Conclusion: Does it really matter? The closest I have ever come to understanding physics was watching EggHead destroy FoggHorn LeggHorn on the Looney Tunes, so forgive my ignorance. I believe it does matter, I believe this pre-rotation helps to stabilize the round prior to it exiting the sizer and barrel. Instead of the round struggling to get the roatation started while in flight, the round is stabilized by pre rotation especially where over bored and rifled barrels alike and cuts through the wind.

Until I have access to slo-mo video with clear barrels I will have to perform ghetto tests like this one.

Ok folks disprove my finding, Ready go!
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Old 05-28-2013, 03:44 PM   #2 (permalink)
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The Lapco rifled barrel starts with the round against the grooves in the barrel so I imagine that barrel will also force the round to spin as soon as it starts moving forward ( It does rotate when pushed through with a stick.)

I too have theorized that the skirt opens up a bit when it is shot. If this is the case it should open more on a tighter bore barrel since the resistance to forward motion is greater. Unfortunately I have not done any testing to confirm or dismiss this yet.
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Old 05-28-2013, 03:48 PM   #3 (permalink)
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Quote:
Originally Posted by The Flounder View Post
The Lapco rifled barrel starts with the round against the grooves in the barrel so I imagine that barrel will also force the round to spin as soon as it starts moving forward ( It does rotate when pushed through with a stick.)

I too have theorized that the skirt opens up a bit when it is shot. If this is the case it should open more on a tighter bore barrel since the resistance to forward motion is greater. Unfortunately I have not done any testing to confirm or dismiss this yet.

Neat-o, so the Lapco IS rifled? Same angle as the fins? Under bore might cause the umbrella effect unless it's so tight there is no room for expansion. I am interested in the round spins when pushed through comment, that is cool.

I know Bill wants to stay away from barrels, I was trying to come up with an idea to support rifled shells. He never said he wasn't going to make shells
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Old 05-28-2013, 03:57 PM   #4 (permalink)
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Neat-o, so the Lapco IS rifled? Same angle as the fins?
It depends on the LAPCO bbl, they have both rifled and non-rifled FSR barrels as well as different barrel IDs.
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Old 05-28-2013, 04:10 PM   #5 (permalink)
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Mine is the one they released at PBE this year. It is a .683 rifled cocker threaded with a small counter bore to allow the FSR into the barrel before the rifling begins. The twist is in the right direction for FSR rounds but not the same twist rate.

They told me it was intended to be used with the Empire Tracer. I have found it works very nicely on the SR1. If you would like to borrow it for some testing drop me a PM and we can make something happen.
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Old 05-28-2013, 04:44 PM   #6 (permalink)
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Here are my thoughts on smoothbore FS barrel behavior:
  • High speed video that punkworks collected of rounds exiting a smoothbore barrel, shows them rotating very slowly.
  • Tom Kaye observed that FS Rounds took about 20+ ft after the muzzle for them to spin up to proper, beneficial RPMs.
  • I think it's entirely possible for a round to start spinning in a smoothbore barrel, to some extent but, not necessarily to the point where it matters.
  • Given how hard and brittle this material is, I'd be surprised if the skirts expanded enough to uniformly touch the bore. The forces involved here may be why some rounds with a cracked (but whole) skirt may have catestrophic fin failure. Also, the skirt is starting off canted inwards and, the ribs would act to reinforce the skirt.
  • Given that the widest part of the round is the equator, it is entirely possible for the rounds to tilt, by a very slight amount, causing the fins at least on one side, to interact.

As for the Rifled Barrels (LAPCO/Tiberius and Hammerhead in particular, other similar barrels in general- assuming proper twist direction and bore sizes) here's what I think:
  • Tom Kaye was doubtful that a First Strike Round could be pre-spun in the barrel (due to his previous experiences).
  • Simon "Manike" collected high speed video of FS rounds leaving a LAPCO/Tibierus rifled barrel and, they do in fact leave at a noticibly higher RPM.
  • The twist rate of the LAPCO/Tiberius and Hammerhead barrels are based on the optimal twist rate for a projectile of our size and weight (i.e. paintball at or under 300FPS) and not on the twist rate of the skirt.
  • The twist rate of the skirt probably accounts for air slipping over the fins and not transferring their full force to the rotation.
  • Rifled Barrels tested so far (long and short lapco/tiberius and long Hammerhead) do have a positive influence on accuracy. As for range, chrono testing will need to be done.

My question for your DSA: are the diagonal marks uniformly spread around the I.D. of the sizer?

And for clarity:

LAPCO Produces Rifled .683 Barrels for the Tiberius Arms T8.1 and T9.1, they appeard to be a joint venture as the barrels feature LAPCO and Tiberius Branding. LAPCO just released AC threaded Rifled Barrels in .683 at PB extravaganza.
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Old 05-28-2013, 05:42 PM   #7 (permalink)
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Really enjoyed this discussion. DSA attempts are valiant. I wondered if any one has flourescent liquid and a black light. dip the First strike in the liquid (just the fins), fire the round quickly, use the light, and then quickly rinse the barrel. IMO over bore the FS is better than underboring!
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Old 05-28-2013, 05:45 PM   #8 (permalink)
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My theory is that in larger smoothbore barrels, the air pressure from the rear of the round can actually spin the FS backwards until it leaves the barrel and the air pressure of it going forward thru air causes it to spin in the correct direction. The tighter rifled barrels help prevent this causing the round to come out stabilized rather than having to reverse it's spin which is why smoothbores take about 20' to stabilize. I have not done any testing, but in the slow motion video, the air is being blown across the tip of the round, not from the fin end. First Strike tube test 2 - YouTube
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Old 05-28-2013, 10:53 PM   #9 (permalink)
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UV I think you are onto something regarding the possibility of the round tilting in the barrel. In fact it is possible that it bangs its way down the barrel catching a fin here or there leaving marks. I say this because the markings are not universal but rather like a fin-spin mark. However in the same breath I wonder if the fact that the round tilts helps to cause the rounds fin to dig in ever so slightly to involk the spin.

Does that make sense?

Tilt is bad, but tilt cause fin to catch, thus causing round to spin, thus tilt is good?

I say, I say boy, I actually had aFoghorn Leghorn/ Egg Head moment.


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My theory is that in larger smoothbore barrels, the air pressure from the rear of the round can actually spin the FS backwards until it leaves the barrel and the air pressure of it going forward thru air causes it to spin in the correct direction. The tighter rifled barrels help prevent this causing the round to come out stabilized rather than having to reverse it's spin which is why smoothbores take about 20' to stabilize. I have not done any testing, but in the slow motion video, the air is being blown across the tip of the round, not from the fin end. First Strike tube test 2 - YouTube
That is a cool theory. I noticed when I poured the powder in on the second test I heard a noticeable spin, similar to the zip sound one hears when placing a razor blade between an HE round and the fuse. I suspect I heard the zip because the powder brought down the decibel level. It was wayyy quiet. This video proves one point, regardless of point of exit, wind will cause spin.


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Originally Posted by Chicago View Post
Really enjoyed this discussion. DSA attempts are valiant. I wondered if any one has flourescent liquid and a black light. dip the First strike in the liquid (just the fins), fire the round quickly, use the light, and then quickly rinse the barrel. IMO over bore the FS is better than underboring!
Yes very cool indeed, tell me do you think wax might yield the same results? You got me thinking, time for another ghetto test....

Parameters:

SR-1

68.5 Shell

FSR

Wax Paper

Soft melted candle wax

Test, pour candle wax on wax paper. Allow to dry softly. Roll FSR over warm surface.

Record results....
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Old 05-29-2013, 12:16 AM   #10 (permalink)
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Originally Posted by DSA View Post
UV I think you are onto something regarding the possibility of the round tilting in the barrel. In fact it is possible that it bangs its way down the barrel catching a fin here or there leaving marks. I say this because the markings are not universal but rather like a fin-spin mark. However in the same breath I wonder if the fact that the round tilts helps to cause the rounds fin to dig in ever so slightly to involk the spin.

Does that make sense?

Tilt is bad, but tilt cause fin to catch, thus causing round to spin, thus tilt is good?

I say, I say boy, I actually had aFoghorn Leghorn/ Egg Head moment.




That is a cool theory. I noticed when I poured the powder in on the second test I heard a noticeable spin, similar to the zip sound one hears when placing a razor blade between an HE round and the fuse. I suspect I heard the zip because the powder brought down the decibel level. It was wayyy quiet. This video proves one point, regardless of point of exit, wind will cause spin.




Yes very cool indeed, tell me do you think wax might yield the same results? You got me thinking, time for another ghetto test....

Parameters:

SR-1

68.5 Shell

FSR

Wax Paper

Soft melted candle wax

Test, pour candle wax on wax paper. Allow to dry softly. Roll FSR over warm surface.

Record results....

For god sake Jim, your going to kill us all.
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