14 Aug 2006 14:17:59
Bill Pelka
Ballistic Coefficient...

Can some one point me to OR enlighten me on the term Ballistic
Coefficient? I found a chart that contained specific pellet, Pellet weight,
speed, and BC. The BC seemed to change either with speed or weight of the
pellet. Is BC dependant on shape (length, width, diameter) or is it a fixed
value? And does the method of propulsion matter? It appears to me that if
each brand of pellet, such as a Beeman Crow Magnum in .22 cal, that weighs
18.2 gr, and has a hollow point shape might/should/would have its own BC. Is
that correct?

I have been shooting Crosman Copperhead .22 cal, 14.3 gr, pointed head
pellets at some tree squirrels in eastern Washington and have been happy
with the results. I ordered a Shooting Chrony Beta Master Sunday and should
be able to get some shooting in this weekend. I am shooting a RWS Mod 54. I
have the RWS 450 Scope (3-9 x 40AO). The chart that I saw had a RWS 94
shooting the copperheads at about 720-750 and claimed a BC of .024. Does
this sound right?

Thanks,
Bill






14 Aug 2006 07:41:33
Re: Ballistic Coefficient...


Bill Pelka wrote:
> Can some one point me to OR enlighten me on the term Ballistic
> Coefficient? I found a chart that contained specific pellet, Pellet weight,
> speed, and BC. The BC seemed to change either with speed or weight of the
> pellet. Is BC dependant on shape (length, width, diameter) or is it a fixed
> value? And does the method of propulsion matter? It appears to me that if
> each brand of pellet, such as a Beeman Crow Magnum in .22 cal, that weighs
> 18.2 gr, and has a hollow point shape might/should/would have its own BC. Is
> that correct?
>
> I have been shooting Crosman Copperhead .22 cal, 14.3 gr, pointed head
> pellets at some tree squirrels in eastern Washington and have been happy
> with the results. I ordered a Shooting Chrony Beta Master Sunday and should
> be able to get some shooting in this weekend. I am shooting a RWS Mod 54. I
> have the RWS 450 Scope (3-9 x 40AO). The chart that I saw had a RWS 94
> shooting the copperheads at about 720-750 and claimed a BC of .024. Does
> this sound right?
>

In the old days, BC was calculated using the formula:

C = M / CdA

where:

C = ballistic coefficient
M = Mass
A = cross-sectional area
Cd = Cd factor



The Cd factor is the shape of the pellet. Considering most pellets are
somewhat similar in shape, you can see that the BC of a pellet is
generally determined by the weight.

However, there is also the issue of supersonic versus subsonic
velocities. The BC of a bullet does vary with speed. For your
purposes the BC of a subsonic pellet doesn't vary greatly as your
bullet slows down.

The BC for the Copperhead looks normal for a 14 grain pellet.

Jimmy Boy



14 Aug 2006 14:56:00
Ernie Willson
Re: Ballistic Coefficient...

jim_hallerud@yahoo.com wrote:
> Bill Pelka wrote:
>
>>Can some one point me to OR enlighten me on the term Ballistic
>>Coefficient? I found a chart that contained specific pellet, Pellet weight,
>>speed, and BC. The BC seemed to change either with speed or weight of the
>>pellet. Is BC dependant on shape (length, width, diameter) or is it a fixed
>>value? And does the method of propulsion matter? It appears to me that if
>>each brand of pellet, such as a Beeman Crow Magnum in .22 cal, that weighs
>>18.2 gr, and has a hollow point shape might/should/would have its own BC. Is
>>that correct?
>>
>> I have been shooting Crosman Copperhead .22 cal, 14.3 gr, pointed head
>>pellets at some tree squirrels in eastern Washington and have been happy
>>with the results. I ordered a Shooting Chrony Beta Master Sunday and should
>>be able to get some shooting in this weekend. I am shooting a RWS Mod 54. I
>>have the RWS 450 Scope (3-9 x 40AO). The chart that I saw had a RWS 94
>>shooting the copperheads at about 720-750 and claimed a BC of .024. Does
>>this sound right?
>>
>
>
> In the old days, BC was calculated using the formula:
>
> C = M / CdA
>
> where:
>
> C = ballistic coefficient
> M = Mass
> A = cross-sectional area
> Cd = Cd factor
>
>
>
> The Cd factor is the shape of the pellet. Considering most pellets are
> somewhat similar in shape, you can see that the BC of a pellet is
> generally determined by the weight.
>
> However, there is also the issue of supersonic versus subsonic
> velocities. The BC of a bullet does vary with speed. For your
> purposes the BC of a subsonic pellet doesn't vary greatly as your
> bullet slows down.
>
> The BC for the Copperhead looks normal for a 14 grain pellet.
>
> Jimmy Boy
>
Jims answer is essentially correct and most likely all you need to know.
To put a little finer point on it...Basically the ballistic coefficient
can be thought of as the ratio of the inertia forces trying to keep a
projectile going at the same speed to the drag forces trying to slow it
down. The higher the BC the better the projectile "hangs on" to
velocity. Projectiles traveling at the same speed and having the same
BCs will slow down at the same rate. Actually, Cd normally stands for
"drag coefficient" and is dependent on the projectile shape and
velocity. All other things equal, pointed pellets generally have higher
BC's that flat pointed ones (of the same weight). For normal air gunning
purposes the BC of any particular projectile is relatively constant
because most pellets are subsonic. If they traveled at supersonic speeds
then several BC might be necessary to describe the projectile ballistics.

The "Chairgun" program lists the BC for 22 cal Crow Magnums as 0.022,
and the BC for Crosman Pointed 22 cal as 0.024.

HTH,
EJ in NJ


14 Aug 2006 16:54:56
Re: Ballistic Coefficient...


Bill Pelka wrote:
> Can some one point me to OR enlighten me on the term Ballistic
> Coefficient? I found a chart that contained specific pellet, Pellet weight,
> speed, and BC. The BC seemed to change either with speed or weight of the
> pellet. Is BC dependant on shape (length, width, diameter) or is it a fixed
> value? And does the method of propulsion matter? It appears to me that if
> each brand of pellet, such as a Beeman Crow Magnum in .22 cal, that weighs
> 18.2 gr, and has a hollow point shape might/should/would have its own BC. Is
> that correct?
>
> I have been shooting Crosman Copperhead .22 cal, 14.3 gr, pointed head
> pellets at some tree squirrels in eastern Washington and have been happy
> with the results. I ordered a Shooting Chrony Beta Master Sunday and should
> be able to get some shooting in this weekend. I am shooting a RWS Mod 54. I
> have the RWS 450 Scope (3-9 x 40AO). The chart that I saw had a RWS 94
> shooting the copperheads at about 720-750 and claimed a BC of .024. Does
> this sound right?
>
> Thanks,
> Bill
//

Tut writes:

For old retired engineers, BC is a mathematical exercise. ;-)) For
ammunition manufactures, BC provides an easier way to calculate
ballistics tables for various ammo they produce by using algebra vice
calculus.

For the average pellet gun shooter (me included) it means nothing,
other than to know a pellet with a higher BC will maintain it's
velocity down-range longer, when compared to similiar pellet with a
lower BC.

Hope this helps!

Tut



15 Aug 2006 14:53:26
Bill Pelka
Re: Ballistic Coefficient...

Thanks for all the replies about BC. I did download the Chair Gun 2 software
program. It helps with the table of BC vs Pellets by different Mfgr's. It
will be interesting to do some shooting with my Chrony Beta Master and some
of the various .22 cal pellets that I have. It will be interesting to
compare my values vs Software and Mfgr's. Also should be fun to see what
energy I start with at the Muzzle and what I end up with 50 yds later...

Thanks again for the replies..
Bill


<cnctutwiler@wmconnect.com > wrote in message
news:1155599696.576511.56980@74g2000cwt.googlegroups.com...
>
> Bill Pelka wrote:
>> Can some one point me to OR enlighten me on the term Ballistic
>> Coefficient? I found a chart that contained specific pellet, Pellet
>> weight,
>> speed, and BC. The BC seemed to change either with speed or weight of the
>> pellet. Is BC dependant on shape (length, width, diameter) or is it a
>> fixed
>> value? And does the method of propulsion matter? It appears to me that if
>> each brand of pellet, such as a Beeman Crow Magnum in .22 cal, that
>> weighs
>> 18.2 gr, and has a hollow point shape might/should/would have its own BC.
>> Is
>> that correct?
>>
>> I have been shooting Crosman Copperhead .22 cal, 14.3 gr, pointed head
>> pellets at some tree squirrels in eastern Washington and have been happy
>> with the results. I ordered a Shooting Chrony Beta Master Sunday and
>> should
>> be able to get some shooting in this weekend. I am shooting a RWS Mod 54.
>> I
>> have the RWS 450 Scope (3-9 x 40AO). The chart that I saw had a RWS 94
>> shooting the copperheads at about 720-750 and claimed a BC of .024. Does
>> this sound right?
>>
>> Thanks,
>> Bill
> //
>
> Tut writes:
>
> For old retired engineers, BC is a mathematical exercise. ;-)) For
> ammunition manufactures, BC provides an easier way to calculate
> ballistics tables for various ammo they produce by using algebra vice
> calculus.
>
> For the average pellet gun shooter (me included) it means nothing,
> other than to know a pellet with a higher BC will maintain it's
> velocity down-range longer, when compared to similiar pellet with a
> lower BC.
>
> Hope this helps!
>
> Tut
>