Canadian Airgun Forum :: ballistic coefficient question

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Author:	Ninjababy [ Mon Feb 25, 2019 9:30 pm ]
Post subject:	ballistic coefficient question
Hey guys, is there any way to find the BC of the pellets? or how do you guys find the drop of the pellets at different distances? Thanks

Author:	Dukemeister [ Mon Feb 25, 2019 9:55 pm ]
Post subject:	Re: ballistic coefficient question
Download and use Chairgun Pro. https://www.hawkeoptics.com/chairgun-an ... -life.html

Author:	Daryl [ Tue Feb 26, 2019 3:26 pm ]
Post subject:	Re: ballistic coefficient question
or use 2 chronographs, for accuracy, one set near the muzzle, the next one at 100yards from the first - or a specified distance - then do the math of the vel. lost. I use ChairGun.

Author:	Ninjababy [ Tue Feb 26, 2019 7:29 pm ]
Post subject:	Re: ballistic coefficient question
Thanks guys. I got the BC from the Chairgun app and then I used my "Ballistic Advance Edition" app to find the drop. I will verify that distances at the range soon.

Author:	Daryl [ Tue Feb 26, 2019 11:37 pm ]
Post subject:	Re: ballistic coefficient question
The chairgun program will set out the drop every 5 yards or meters if you want it to with whatever kill zone (area brackets) you want.

Author:	Chevota [ Sun Mar 10, 2019 7:19 pm ]
Post subject:	Re: ballistic coefficient question
I thought I posted on this already, but fyi Chairgun can't calc trans sonic. At least not when I used it last which has been a while. I doubt it ever will but who knows. This means you plug in a known # for a pellet, like .020, it'll be ok <890fps, but it won't factor the BC change when you go above ~890fps, and that # changes steadily up to 1130 or somewhere which is drastically diff. So if you're up in that zone you'll have a hella time figuring out your pellets BC because the pellet will slow more quickly at first, then less quickly as it slows until you get ~890. BC still changes at <890, but to a much lesser degree. If you look at BC #'s people post online you'll see they vary, drastically. It depends on so many factors, then add human error and misc errors, so you get drastically diff #'s. All that matters imo is you choose one with good BC that you like, then learn how much it drops at xx distances in your gun. Not much else you can really do. If you really want the BC #'s then you'd need two Crony's, accurate distance measuring, and lots of time. Also be certain both crony's are matched, so shoot with one in front, then trade places to confirm they each read equally. Typically the second one will read less, just be sure the front and rear show the same diff regardless of which is in front/back.

Author:	Daryl [ Sun Mar 10, 2019 8:09 pm ]
Post subject:	Re: ballistic coefficient question
A lot of these air-gun ballistics are new to me. Much of my shooting is over 3,000fps and some well over 4,000fps, where I've found an on-line chart that works perfectly with my bullets and loads, out to 1,000 yards/meters. It also works for the .17 cal pills, too (at 3,600fps to 4,500fps), out to 500 yard gophers anyway. The only deterrent to this type of program is you have to know the BC before hand. Knowledge of atmospheric conditions also makes a difference but is less important than the BC. BC's can be found in most bullet maker's manuals or on their web sites. Finding the actual numbers from people who set up multiple chronographs, usually shows lower numbers than mfgr's claims. Plugging in the 'proven' #'s usually gets drop figure accuracy to fractions of an inch. This is the one I use for PB guns. It has worked well for me. http://www.shooterscalculator.com/balli ... ate+Chart+

Author:	rsterne [ Sun Mar 10, 2019 10:18 pm ]
Post subject:	Re: ballistic coefficient question
ChairGun has improved drastically over the years.... When I first did my testing and calculated BCs using the first ChairGun, I found huge changes in the BC as the velocity approached Mach 1, because ChairGun was using a drag model that used a constant drag coefficient.... Since the Cd varies by a factor of 3-5 in the Transonic region (Mach 0.8-1.2), for all projectiles, this gave terrible results.... Later versions of ChairGun used the G1 drag model, designed for bullets, which compensates somewhat for that rapid drag rise.... The latest version can use a drag profile called GA, which is designed to be even closer to airgun pellets.... so if you do a BC measurement using the latest version of ChairGun it is about the best out there.... Unfortunately, ChairGun has been discontinued by Hawke.... The "Legacy Version" may still be available for download on their website, but they have announced they will no longer be updating it, nor even changing it to be compatible with changes to operating systems, in the future.... It has a BC calculator built in, and it's the best that we have currently.... For how much longer is anybody's guess.... https://www.hawkeoptics.com/chairgun-an ... -life.html Bob

Author:	Daryl [ Sun Mar 10, 2019 10:28 pm ]
Post subject:	Re: ballistic coefficient question
tks for the information, Bob.

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