Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: a question for the ballistitians

  1. #1

    a question for the ballistitians

    Hi all, in the sierra data they give different ballistic coefficients for different velocities for every one of there bullets, nobody else seems too, would these velocities be relative or very similar for other bullets. Swaro

  2. #2
    Quote Originally Posted by swarovski View Post
    Hi all, in the sierra data they give different ballistic coefficients for different velocities for every one of there bullets, nobody else seems too, would these velocities be relative or very similar for other bullets. Swaro

    There was a time when Dupont put out sheets of bullet "forms" so that a shooter could match his or her bullet to the form as closely as possible and plug in a BC so, in that sense, yes: It's relevant. Sierra A 150 grain Game King flat base probably has a very similar BC to a Speer 145 grain Hot Cor 7mm bullet based on a fairly similar form and weight.

    It will be close, but not exact. For coarse work it's an OK starting point. For serious work, you won't even take Sierra's word and you'll calculate your own BC.~Muir

  3. #3
    I assume that the highest figures are max bc that bullet will be no matter how fast it goes.

  4. #4
    Quote Originally Posted by swarovski View Post
    I assume that the highest figures are max bc that bullet will be no matter how fast it goes.
    I'm not sure what you mean but yes, within that range of velocity listed at least the BC listed is the best you can count on.~Muir

  5. #5
    The Sierra figures, I think, reflect the "G1" model of the bullet which is a cylindrical flat based thing with a rudimentary point that does not properly reflect the more modern (since about WW1) streamlined designs. You find figures from subsonic, supersonic and high-supersonic to reflect this. Most other manufacturers just quote the lowest drag value. If, like Sierra, you're flogging a software package with trajectory calcs then knowing the BC at various velocities should allow a better model to be built.

    Have a look here: Ballistic coefficient - Wikipedia, the free encyclopedia

  6. #6
    I think the 6.5 cal 142gr smk is a fairly modern bullet, one of the highest bc 6,5 cal bullets you can get,2860fps and above is 0.595bc, lower than that velocity the bc deminishes

  7. #7
    Ive tried the g7 bc on my bal cals and they are way off, g1 bc's are very very close to actual as I shoot out to 1000yds thats a good yard stick to measure with.unless I am doing something badly wrong with the g7 figures which I cant see what as all I am doing is changing from one to the other on the bal cal, not changing anything else.

  8. #8
    Quote Originally Posted by Muir View Post
    There was a time when Dupont put out sheets of bullet "forms" so that a shooter could match his or her bullet to the form as closely as possible and plug in a BC so, in that sense, yes: It's relevant. Sierra A 150 grain Game King flat base probably has a very similar BC to a Speer 145 grain Hot Cor 7mm bullet based on a fairly similar form and weight.

    It will be close, but not exact. For coarse work it's an OK starting point. For serious work, you won't even take Sierra's word and you'll calculate your own BC.~Muir
    The man is correct again. Best to work it out yourself you will be surprised how far off it will be. To be honest it's the last thing I look for in a hunting bullet.

    http://www.jbmballistics.com/cgi-bin/jbmbcv-5.1.cgi

  9. #9
    Quote Originally Posted by swarovski View Post
    Ive tried the g7 bc on my bal cals and they are way off, g1 bc's are very very close to actual as I shoot out to 1000yds thats a good yard stick to measure with.unless I am doing something badly wrong with the g7 figures which I cant see what as all I am doing is changing from one to the other on the bal cal, not changing anything else.
    At one time Sierra used a C1 drag coefficient as did Speer, iirc, which is very similar to the G1. There are dozens of different drag factors out there but most ballistic calcs are for G1. The G1 works for you so the answer is plain....~Muir

  10. #10
    Quote Originally Posted by swarovski View Post
    Ive tried the g7 bc on my bal cals and they are way off, g1 bc's are very very close to actual as I shoot out to 1000yds thats a good yard stick to measure with.unless I am doing something badly wrong with the g7 figures which I cant see what as all I am doing is changing from one to the other on the bal cal, not changing anything else.
    I tried comparing the Berger model with my more usual Sierra V5 and the difference isn't that much in my opinion.

    This is Berger's G7 variant
    Click image for larger version. 

Name:	Berger_77_223_3000_G7.jpg 
Views:	6 
Size:	118.4 KB 
ID:	50537

    This is Berger's G1 version
    Click image for larger version. 

Name:	Berger_77_223_3000_G1.jpg 
Views:	3 
Size:	120.1 KB 
ID:	50538

    And Sierra V5 (not a slightly different BC but not much IMO)
    Click image for larger version. 

Name:	Sierra_77_223_3000_G1.jpg 
Views:	3 
Size:	131.2 KB 
ID:	50539

    To me, close enough. One thing I thought about and checked: if fiddling with G7 the bullet is streamlined (i.e. boat tail) as the the G1 is more like a conventional flat base. In fact Berger only quote G1 BCs for the FB bullets.

Similar Threads

  1. a question for the ballistitians
    By swarovski in forum Ammunition, Reloading & Ballistics
    Replies: 13
    Last Post: 18-06-2014, 11:37
  2. another question for the ballistitians
    By swarovski in forum Ammunition, Reloading & Ballistics
    Replies: 1
    Last Post: 18-06-2014, 06:53
  3. A Question
    By Kit in forum Deer Dogs & Tracking
    Replies: 3
    Last Post: 29-05-2014, 06:26
  4. Quick Question in DSC1 question bank (97)
    By AndrewW in forum Training and Qualifications
    Replies: 8
    Last Post: 31-01-2013, 22:40
  5. Question??
    By Thomo8 in forum Deer Stalking General
    Replies: 10
    Last Post: 24-09-2012, 18:44

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •