Chad Schmidt
Well-Known Member
Being new to this I'd like some input on the minimum BC for elr shooting. I appreciate your input.
Chad
Chad
Thoughts on minimum BC
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gohring3006
Well-Known Member
It's all velocity dependent.
A bullet going 2600fps with a very high bc, say .650 can and will be outperformed by a bullet with a hypothetical .550 going 3300 FPS, in the same caliber/cartridge.
A ballistic calculator helps with determinating a bullets performance with in your local atmosphere parameters. Most are going with a minimum velocity of 1800fps at impact for bullet performance and 1000-1500 ft lbs.
A bullet going 2600fps with a very high bc, say .650 can and will be outperformed by a bullet with a hypothetical .550 going 3300 FPS, in the same caliber/cartridge.
A ballistic calculator helps with determinating a bullets performance with in your local atmosphere parameters. Most are going with a minimum velocity of 1800fps at impact for bullet performance and 1000-1500 ft lbs.
KyCarl
Well-Known Member
You can play with this. By changing the FPS..Twist..Elevation,, you can see how the stability changes?
http://www.bergerbullets.com/twist-rate-calculator/
http://www.bergerbullets.com/twist-rate-calculator/
BallisticsGuy
Well-Known Member
Different people have different definitions of ELR which will pollute the discussion a bit. Velocities in common modern high power rifles ranging from <2400->3400fps also pollutes the possible answer set with if's and but's. We can clean up the discussion by limiting our conversation to a parameterized set of values and things clear up a little.
There's a relatively narrow window of common velocities that one might expect from a modern high power rifle that's going to be used for long range work. If you focus on the slow side of that then the question is easier to answer in an apples-to-apples way. I'm using 2400fps for this example: BC's under .450 G1 makes for limiting supersonic range to a good bit under 1000yrds, not much more than 800 actually. At .500 G1 you're just getting 1000yrds supersonic. By .550 G1 you're out to around 1100yrds. By .600 G1 you're dealing with a bullet that will get to around 1200yrds supersonic. At .650 G1 you're around 1300yrds. Additional velocity extends those range numbers. Velocity comes at the cost of powder, barrel wear, recoil and blast. This is why the 6.5CM is so lauded. Modest velocities and the pretty high BC #'s common to mid-to-heavy weight 6.5mm bullets makes for a ton of supersonic range with a very tolerable cost in powder appetite, barrel wear, recoil and blast.
BC is the thing that allows you to get out as far as you want without having to run the bullet so fast as you otherwise would. Don't get hung up over .005 difference on a BC of one bullet versus another.
There's a relatively narrow window of common velocities that one might expect from a modern high power rifle that's going to be used for long range work. If you focus on the slow side of that then the question is easier to answer in an apples-to-apples way. I'm using 2400fps for this example: BC's under .450 G1 makes for limiting supersonic range to a good bit under 1000yrds, not much more than 800 actually. At .500 G1 you're just getting 1000yrds supersonic. By .550 G1 you're out to around 1100yrds. By .600 G1 you're dealing with a bullet that will get to around 1200yrds supersonic. At .650 G1 you're around 1300yrds. Additional velocity extends those range numbers. Velocity comes at the cost of powder, barrel wear, recoil and blast. This is why the 6.5CM is so lauded. Modest velocities and the pretty high BC #'s common to mid-to-heavy weight 6.5mm bullets makes for a ton of supersonic range with a very tolerable cost in powder appetite, barrel wear, recoil and blast.
BC is the thing that allows you to get out as far as you want without having to run the bullet so fast as you otherwise would. Don't get hung up over .005 difference on a BC of one bullet versus another.
RockyMtnMT
Official LRH Sponsor
As said by the others there is a lot of blanks in your question to really give a good answer. I assume you are talking hunting not target? What are you hunting, varmints or elk? How far is elr? (this is a varying value totally dependent on the individual)
As a bullet maker the terminal performance characteristics of the bullet should be a big part of the decision making. If shooting varmints and targets then the choice is less cloudy. Just run a ballistics calculator with different bullets and the expected vel from your cartridge to figure out what bullet gets you on target.
Will be an interesting thread. Could go well, could get sideways.
Steve
Hand Skills
Well-Known Member
I like the German Salazar quote;
"Muzzle velocity is a depreciating asset all the way to the target; a high BC, like diamonds, is forever."
In that context, it's kind of like debating 'what's the minimum size diamond required for an engagement ring'.
BC doesn't just help with retained velocity, it also helps minimize the effects of wind drift.
A G7 BC of .400 is pretty good
"Muzzle velocity is a depreciating asset all the way to the target; a high BC, like diamonds, is forever."
In that context, it's kind of like debating 'what's the minimum size diamond required for an engagement ring'.
BC doesn't just help with retained velocity, it also helps minimize the effects of wind drift.
A G7 BC of .400 is pretty good
DocUSMCRetired
Well-Known Member
It depends on needs. A low BC bullet shot at a fast speed (BC is weight dependent, and adding weight gives you a slower muzzle velocity) can create a larger danger space. In simple terms, a light weight low BC bullet can be extremely flat at close ranges. Kind of like the 22-250 for varmint hunting.
However that higher BC, heavier, slower bullet will have an "overtaking" moment. Where down range at some point that heavier bullet will surpass the velocity of the lower BC bullet. After that point, the higher BC bullet which started out slower will out perform the lower the BC bullet from then on. The higher BC bullet retains velocity better, but might start out slower due to being heavier. So it just needs to reach the overtaking point where the lower BC bullet has lost velocity.
Which one to chose depends entirely on the situation and needs. Other things also impact decisions. Like bullet length, seating depth, use of single or magazine loaders.
However that higher BC, heavier, slower bullet will have an "overtaking" moment. Where down range at some point that heavier bullet will surpass the velocity of the lower BC bullet. After that point, the higher BC bullet which started out slower will out perform the lower the BC bullet from then on. The higher BC bullet retains velocity better, but might start out slower due to being heavier. So it just needs to reach the overtaking point where the lower BC bullet has lost velocity.
Which one to chose depends entirely on the situation and needs. Other things also impact decisions. Like bullet length, seating depth, use of single or magazine loaders.
Chad Schmidt
Well-Known Member
Thank you, in some ways all the answers you all have made a list of things for me to consider that has been a great deal of help. I appreciate your willingness to help me get up to speed. God bless you all.
HARPERC
Well-Known Member
I work backwards from a goal, eliminating that which plainly is detrimental to the goal, ignore what doesn't matter, weigh the plus and minuses of the relevant parameters.
Chad Schmidt
Well-Known Member
That is how I'll use the list of things to take into consideration to do. I plan to use LRAB and LRX bullets for 6.5, 7mm and 30 caliber in various chambering. So working from the goal backwards will be the best approach to achieve the intended goal.
