General Category > Airgun Ammo

BC of Airgun Slugs

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rsterne:
We are slowly learning that the G1 ballistics model is not the best match for airgun slugs, particularly the current designs of swaged slugs with a 2S tangent Ogive and about a 50% Meplat.... However, until a better model (eg. that proposed by Miles Morris) is established and becomes commonplace, it is the one most of us use.... I was looking at the HAM database of BC's this morning, and found something interesting in the section on .22 cal Slugs.... You can find it here....

https://hardairmagazine.com/ballistic-coefficients/

You can sort the table by any of the columns by clicking on the column heading.... If you sort by the "Form Factor" (and you can have low or high at the top), you will see something interesting.... The range of values only goes from 0.89 to 1.06, with the average being 0.97.... That means that if you use the Sectional Density as your BC, you will be pretty close for any of them.... The worst case would be an error of 11%....  8)

A lower FF means less drag for a given weight, and therefore a higher BC.... However, with the mismatch we see between the velocity during testing and what the actual drag is at the velocity you are using because the G1 profile doesn't suit our slugs very well, that method of estimating the BC should be close enough.... Interestingly, I have been doing that for years....  ;)

Bob

Alan:
You now have a means of measuring (calculating) the BC. The question remains, have you done any testing yourself?

rsterne:
I have done a limited amount, but nowhere near as much as I would like.... Currently I am waiting until I can cross the US Border to get some more lead, as I cannot cast any more because I have run out....  ::)

Bob

JungleShooter:
Someone send a lead truck over to Canada so Bob can make more slugs!!  😊


🔷 Bob, I'm not sure if I mentioned this, but there is a new ballistic calculator out.
It incoroporated Mile's experimental drag model for pellet and for slugs.



🔶 It's the "GPC Ballistics Applications".
It's a full suite,
for Windows, Android, iOS, Linux
I have it on my Android phone, where it installs as about a dozen separate apps. I don't know how it installs on a Windows computer, mabye all integrated into one program?


🔶It's very powerful, with a lot of very conventient functions that ChairGun offers for the Windows version — but that it cut out for the mobile version (phones and tablets).


🔶The developer of the ballistic caculator is active on UK forums, and did this project out of boredom when he was recovering from an injury he said.  🤣


🔶Here is the webpage of the developer where you can download the different apps/ versions:

https://GPC.fotosoft.co.uk/Home.html

Matthias


rsterne:
I have one called "Easy BC" which also has Miles' Drag Models in it....

Bob

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