Paintball Spin Physics - Getting to the final Answer

[Robotech]

Well wait a minute...I thought I saw somewhere on the FN303 information page that the rounds are spun to increase accuracy and distance???

The next question would be that if the barrel wasn't implementing the spin then what was? What was causing the rounds to behave the way they were? I mean, if it were just a matter of weight and no spin was involved then wouldn't a heavier paintball show the same accuracy as the FN303 rounds since we are seeing these results with the lighter rounds? These results would seem to lead to the conclusion that there are forces acting on the ball that are greater than the vortexes we see on a round ball thus pushing the lighter round further off course but not affecting the heavier round.

It sounds to me like there may be something else at work here. hmmmmmmmm.

[manike]

Well wait a minute...I thought I saw somewhere on the FN303 information page that the rounds are spun to increase accuracy and distance???

The next question would be that if the barrel wasn't implementing the spin then what was? What was causing the rounds to behave the way they were? I mean, if it were just a matter of weight and no spin was involved then wouldn't a heavier paintball show the same accuracy as the FN303 rounds since we are seeing these results with the lighter rounds? These results would seem to lead to the conclusion that there are forces acting on the ball that are greater than the vortexes we see on a round ball thus pushing the lighter round further off course but not affecting the heavier round.

It sounds to me like there may be something else at work here. hmmmmmmmm.

The rounds are spun because they have fins on them. If you search for Musikman's thread on his FN303 in Paintball talk you will see pictures of the rounds.

Heavier paintballs are more accurate. Same vortex force will have less effect on a heavier round. F=MA.

[Robotech]

Ahhhhh...I have seen the rounds and saw the fins but did not know they were there to impart the spin.

I also realize that a heavier round will be less resistant to the force the vortex applies to it thus being more accurate.

So does this mean that when the lighter weight round was spun using the same fins (again, assuming that the round we are talking about here is identical in shape and form as the FN303 rounds and the only difference is weight) that this spin is what caused its erratic behavior?

Not trying to sound stupid...just trying to get my head around why this design change in a similarly weighted paintball would make its accuracy WORSE than when it was perfectly round. I can understand its accuracy not being as good as a heavier round, but I would still think there would be an improvement in accuracy over a round ball of equal weight. I would have never thought it would actually get worse. (BTW, F=MA is that Force=Mass * Acceleration? If so I'm amazed something from my HS physics class actually took! LOL)

[justjoshin590]

if by lighter rounds do you mean the ones that manike made? if so then its my opinion that if they were simply setup so the front was heavier than the back, that it would still work

[Robotech]

Right. The FN303 rounds are 8 grams because they couldn't get the performance they wanted from lighter rounds. My question is was there any difference in performance and if so, how much? From what I'm reading here it sounded like they were worse but I don't know if these rounds were the exact same as the FN303 rounds but lighter or just "close proximities" to the FN303 rounds.

[manike]

Right. The FN303 rounds are 8 grams because they couldn't get the performance they wanted from lighter rounds. My question is was there any difference in performance and if so, how much? From what I'm reading here it sounded like they were worse but I don't know if these rounds were the exact same as the FN303 rounds but lighter or just "close proximities" to the FN303 rounds.

Are you questioning my ability to reverse engineer?



Only difference in these rounds is what they were made from and how they were weighted.

[Robotech]

Are you questioning my ability to reverse engineer?



Only difference in these rounds is what they were made from and how they were weighted.

Would never dream of it!

That's what I was afraid of though. That just blows my mind though that it made the accuracy worse than a regular paintball. I wonder why.

[manike]

Would never dream of it!

That's what I was afraid of though. That just blows my mind though that it made the accuracy worse than a regular paintball. I wonder why.

Possibly because without the weighted front the spin made them tumble.

At tumbling FN303 round is going to have far more issues than a tumbling paintball which still presents the same cross section.

This has been known to happen with some air pellet designs. (used to be big into air gun shooting with lead pellet as a kid).

[Muzikman]

Simon, when you made those rounds, did you use the dimensions I gave you?

[SlartyBartFast]

Possibly because without the weighted front the spin made them tumble.

I think the problem is the center of gravity. The nylon rounds are back heavy. You need to have the center of gravity forward enough so that in flight, the backend isn't trying to become the bottom. With the back end too heavy, the spin axis is offset from the center axis of the round and there is a lot of drag from the finned end = unstable flight.

How about trying to drill out the back of the rounds to move the center of gravity forward.

That would also explain why the front half of a "normal" FN303 round is where the majority of the weight is placed. I'm almost positive that the final weight was not calculated to get a certain impact, but was what was required to sufficiently balance the desired payload.

[manike]

Simon, when you made those rounds, did you use the dimensions I gave you?

Yes and checked them against some stuff in NJ. You'd be amazed at what they have here!

I think the problem is the center of gravity. The nylon rounds are back heavy. You need to have the center of gravity forward enough so that in flight, the backend isn't trying to become the bottom. With the back end too heavy, the spin axis is offset from the center axis of the round and there is a lot of drag from the finned end = unstable flight.

How about trying to drill out the back of the rounds to move the center of gravity forward.

That would also explain why the front half of a "normal" FN303 round is where the majority of the weight is placed. I'm almost positive that the final weight was not calculated to get a certain impact, but was what was required to sufficiently balance the desired payload.

I agree.

My next plan was to make some with hollow fronts I could fill, and with hollow rear ends to move the weight around.

I think it's all about the COG, although from past conversations with Tom I believe with the FN303 the weight is also there for impact and accuracy.

[SlartyBartFast]

My next plan was to make some with hollow fronts I could fill, and with hollow rear ends to move the weight around.

Just drill out the back and push a ball bearing into the front.

[manike]

Just drill out the back and push a ball bearing into the front.

Good idea!

I'll look for the largest bearings I can push through from the back whilst still keeping a decent wall thicknes.

[SlartyBartFast]

I'll look for the largest bearings I can push through from the back whilst still keeping a decent wall thicknes.

I only meant to increase the weight to the same as paintball with the weight further foward.

That size sounds like you can remove the moniker "less-than-lethal".

[manike]

I only meant to increase the weight to the same as paintball with the weight further foward.

That size sounds like you can remove the moniker "less-than-lethal".

I'll check but the weight is currently quite comparable to a real paintball.

I also want to make some rounds that are as accurate as possible. I won't be firing at anything other than a target though.

It isn't a "less-than-lethal" gun. It's a "less lethal" gun. Big difference.