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-   -   backspin bolts put on trial (https://www.mcarterbrown.com/forums/ask-experts/43859-backspin-bolts-put-trial.html)

Cockerpunk 06-27-2008 12:20 AM

backspin bolts put on trial
 
intro -

YouTube - Intro to backspin bolts test

test -

YouTube - The Backspin Bolt Test

drg 06-27-2008 04:48 AM

Not that I think it would change the results much, but it is unfortunate you did not use an actual backspin bolt ... the porting on a venturi bolt is far closer to the bolt face's center than the outlet on a true backspin ("low-blow" type) bolt. Given that there isn't much distance to work with between the center and edge of the bolt face, the difference is significant.

Also, I'm not sure I like the choice of a venturi bolt for this test regardless ... seems to me like you're introducing a lot of turbulence, when you are depending on some manner of laminar flow to create spin in the first place. But then again it has been said that no bolt really has much laminar flow (and therefore it would be impossible to generate much spin with the air charge), so maybe it doesn't really matter.

HP_Lovecraft 06-27-2008 08:46 AM

I have more experience with backspin bolts that probobly anyone, as I've used them in nearly all my guns in the last 20 years. They do work exactly the same as the flatline, is done correctly. It is not a myth.

DRG is completely correct. The way the test was designed, it would not show the magnus effect.

In order to generate magnus effect, you need a minimum spin speed to break the "threshhold", or you won't generate any at all. This spin speed is called the reynolds number. In short, plugging those holes will not get you to the Reynolds number.

You would need the hole at the very base, be very small, and have a very overbored barrel. I know because I've made very many of those bolts, and found out the hard way!

Now, the only bolt that actually claims to do with was the CooperT Better bolt.

Other bolts, like the Undertow, or the Alien bolts DO NOT claim to reach Reynolds. INstead, they use a slower speed, and claim to be generated either Bournulli force (with the Alien bolts), or Gyroscopic Inertia (with the undertow bolt).

In the case of the latter bolts, I've never used those, so I can only guess, but with the COoperT , and my own bolts, its definetly measurable, but you have to be very specific. Remember, that Reynolds number is at threshhold. If you do not meet it, you can get a reverse-magus effect (ie Sinking fastballs).

That said, I still think you did a GREAT JOB. DO NOT compare yourself to mythbusters. You actually used some degree of science.

Painthappy 06-27-2008 08:53 AM

Yup... great job... Maybe we can get some Cooper-T's better bolts for you guys to try out!

Did I mention how much I like this place?? Keep up the great work. Lots of brilliant minds at work here.

brycelarson 06-27-2008 09:32 AM

we're certainly willing to test whatever people think is worth looking at.

If anyone has a commercial backspin bolt - or one that they think works - we'll give it a shot.

We'll shortly be asking for test suggestions - and donations of gear or cash for paint. I think that with the resources available on this and other forums we should be able to gear up and test some really great stuff.

For example, this backspin idea - or *GASP* brass vs. other barrel materials....

Schmitti 06-27-2008 09:34 AM

HP ... I have to call you on the Reynolds Number. This is something I used to deal with every day for more than 10 years. The Reynolds Number (Re) is a ratio or the Dynamic Pressure/Shearing Stress. While the effects of the turbulance in the fluid may impart a spin on a solid body in the fluid, the Reynolds Number is not a measure of that spin. In civil engineering we use the Re when calculating flows in pipes and open channels. It's more important in channels as it helps you determine the lining that should be used if going with a natural lined swale (instead of concrete.. blah).

Reynolds number - Wikipedia, the free encyclopedia

Anyways... end enginerd speach.

E

Clearush 06-27-2008 09:45 AM

Alamo city paintball sells a commercial delrin version of a "low blow bolt" for most markers. Definatly quality to thier products.

Delrin bolts and accessories from Alamo City Paintball


edit: the face of these are still open with just a channel milled out on the bottom, but they are a custom shop so the owner may be quite willing to customize any bolts without the center boring. Seems to be a fairly nice guy according to a few people that know him.

HP_Lovecraft 06-27-2008 10:00 AM

Quote:

Originally Posted by Schmitti (Post 438675)
The Reynolds Number (Re) is a ratio or the Dynamic Pressure/Shearing Stress. While the effects of the turbulance in the fluid may impart a spin on a solid body in the fluid, the Reynolds Number is not a measure of that spin.

Your right that I was oversimpifying.

The Reynolds number reflects the Pressure/Stress ratio. But for a round projectile, this directly correlates to the spin.

For example:
https://www.geocities.com/k_achutarao/MAGNUS/fig3.JPG

You can calculate the Re if you know the spin, and size, and mass, and orientation of the seam. SO its not really a threadshold as in itself, but it represents a threshhold if you want to offset gravity.

Its a balancing act, since the Reynolds could, via Magnus, pull a paintball up, but it could also increase friction, through turbulence. They work against each other. But at a certain spin speed, they work together, and thats when you get the benefits.

Same thing applies to golf balls, and baseballs. Fastball with fast backspin is flat. Fastball with slightly slower backspin is a sinker.

Schmitti 06-27-2008 10:18 AM

Oh man... you had to go and pull out the graph on me... you bastard you!

Go back to walking around work with your clipboard and red sharpie and leave the science to the enginerds!

:LMAO:

Back to science... you are using Reynolds to it's fullest extent.... which makes it that much harder. In my work I deal with stationary solids and the moving fluid.... you are dealing with a moving solid and a moving fluid... too far beyond my skills.

Just show me where you want the house, utilities, rail road, etc and I'll figure out the rest.... advanced physics... Forget it!

E

MondoMor 06-27-2008 11:37 AM

Quote:

Originally Posted by Clearush (Post 438676)
Alamo city paintball sells a commercial delrin version of a "low blow bolt" for most markers. Definatly quality to thier products.

Delrin bolts and accessories from Alamo City Paintball


edit: the face of these are still open with just a channel milled out on the bottom, but they are a custom shop so the owner may be quite willing to customize any bolts without the center boring. Seems to be a fairly nice guy according to a few people that know him.

I've got one on a basket-case FASOR that I need to test, but haven't gotten to it yet.

Ron from ACP is indeed an easy guy to deal with.


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