Notifications
Clear all

Pellet BC


Kidpellet
(@kidpellet)
Joined: 3 years ago
Posts: 57
Topic starter  

Has anyone ever gotten a BC of .0475 with a Crosman 14.3 hp shooting at around 745 fps?


Quote
marflow
(@marflow)
Joined: 3 years ago
Posts: 1154

ReplyQuote
Hector J Medina G
(@hector-j-medina-g)
Member of Trade
Joined: 3 years ago
Posts: 651
 
Posted by: @kidpellet

Has anyone ever gotten a BC of .0475 with a Crosman 14.3 hp shooting at around 745 fps?

Nope!

 

Something is wrong with your calculations. Or you are feeding wrong info into the software.

Calculating BC's is tricky because, depending on a number of things, results vary wildly.

Let's take an example from Chairgun (legacy version of the software):

You input the MV: 745

You enter the range: 25 yards (very common backyard range)

Then you finish by entering the Velocity at 25 yards: 655

The result is 0.0241 (which is about what HAM did, just they used LabRadar)

 

Now, let's say that you are using two chronos, and that while the near one reads 3½% high (normal instrumental difference), the far one reads 3½% low. What is important here is that the DIFFERENCE in MV's between the two is measured as 7% lower difference (lower speed loss=higher BC).

And that your range is off by 1 yard:

Under these conditions, what you are reading as 745 is, in reality 771

While what you are reading at 25 yards is 700, but in reality is 668

So, what you get out of the software is a BC of 0.0487

Instead of what you SHOULD be getting that is 0.0220

 

If you calculate BC using POI, you need to get the POI from a substantially significant sample, and that would mean 10 groups of 10 shots at each distance, in order to be truly reliable.

WHY 10 groups of 10 shots ea?

Read this:  https://www.ctcustomairguns.com/hectors-airgun-blog/shot-cycle-dynamics-in-3-spring-piston-airguns-chap-3  

If you want the one-liner conclusion of all the stats is that IF you want to OPTIMIZE the information you get out of 100 shots, you are better off doing 10 X 10 shot groups than 20 X 5, or 5 X 20.

HTH, keep well and shoot straight!

 

 

 

 

 

HM

 


ReplyQuote
Droidiphile
(@droidiphile)
Joined: 3 years ago
Posts: 113
 

It's easy to agree that ballistics research/testing is very complex. Take a look at this link to see the equipment they use to get solid data.  It points out that anything you can do "at home" would be a challenge to get accuracy in results.  They even mention testing fragmentation for "light gas guns" under 1300fps - that would apply to us Airgun Warriors.

People may disagree with this, but I certainly don't place much emphasis on ballistic coefficient for the above reasoning.  As a practical matter, you can shoot or hunt very successfully, and never know the BC of you ammo.


ReplyQuote
Kidpellet
(@kidpellet)
Joined: 3 years ago
Posts: 57
Topic starter  

This guys says he's the man....

I think he's full of it but that's just my opinion.

 

He actually said that Hector's reply was good info to get your feet wet in ballistics!

Screenshot 20210612 082714 Facebook

 


ReplyQuote
Steve in NC
(@steve-in-nc)
Dealer
Joined: 3 years ago
Posts: 455
 
Posted by: @kidpellet

Has anyone ever gotten a BC of .0475 with a Crosman 14.3 hp shooting at around 745 fps?

That's twice the BC I've measured for that pellet at roughly the same MV: 0.025.  Prettymuch the same as the classic Crosman Premier.  Of course the CPHP is a "hollow point" in name only.  I don't think the little dimple on its nose has much effect on ballistics -- external or terminal.


ReplyQuote
Kidpellet
(@kidpellet)
Joined: 3 years ago
Posts: 57
Topic starter  

@steve-in-nc

This is just one aspect of this gentleman's line of crap, I mean false information 


ReplyQuote