B.C.?

[DannoBoone]

This has no doubt been asked before, but does anyone
have the B.C. of the 200gr SST? (Preferably not what T/C
CLAIMS it to be, if it's such an exageration as they have
made for the 250gr Shockwave.)

[RBinAR]

;D What does T/C claim it to be? I spoke to an engineer at Hornady a while back and he gave me a figure just above that of the 250 grain SST of .22 (actually .225 but any third position number is meaningless).

I've never actually measured the 200 grain bullet but I will if necessary. I have measured the 250 grain bullet and .21 or there about is a valid claim.

[DannoBoone]

Someone mentioned on another board that T/C was
claiming something like .234 or .238. Don't recall for sure.
(Gee, hope it wasn't rumor being passed along.)

[edge]

The B.C. is velocity dependent, and that velocity will most likely be different for PISTOL bullets vs RIFLE bullets.

edge.

[Rifleman]

per the hornady website, the bc for the 200 gr sst is .265
Rifleman

[SW]

I'll try to shoot both the 200 and 250 SSTs at 2650 and 2450 '/sec respectively to 300 yards and calculate the BCs of each and report them. Will try to complete within 2 weeks. I suspect the published BCs are calculated at velocities well below 10-ML2 velocities. This would make them relatively inaccurate for our use. Remember that we really need to sight-in at some prefered range and then shoot groups at certain ranges out to our max poss range. This will do two things: 1) let you know the drop at that range so you will know your hold over and, 2) what your rifle will group at that range which might be a limiting factor. Remember your in - the- field groups are significantly larger than our off --the -bench groups. Rifleman, considering your experience, much of this discussion wasn't directed to you. Just a general statement for anyone on this board who might benefit.

[DannoBoone]

SW - Yes, I know there is no substitute for getting out there
and shooting at different ranges to KNOW the trajectory for
one's own rifle, at one's own altitude, etc. It's just
interesting to make the calculations to have an idea, and
to see how close everything comes to those calculations.
Have a range with three different shooting lanes, the
longest right at 300yds for doing just that! ;D

[Rifleman]

To sw, That was a very kind remark, but let me make my position a little more clear. I miss, just like everybody else. Ha sometimes more ! cause I shoot. I shot a wrong target at the 600 yd line in a match one day, and it cost me a medal !! it happens.And I shoot better of the bench then from position too, but I can say my prone is mighty darn close to my bench, but then again in a match we are constrained by the rules, in the field we try to get every advantage, use bipods,rests whatever, heck I shot a deer using my son as a rest, whatever works.But also there are quite a few guys here that could hold their own I am sure in any rifle match after gettting used to that particular game. anyway, You are certainly correct in saying field accuracy is a whole different ballgame then bech resting at the range, anyway,thanks for the kind remark.
my 2 cents on bc's. they have 2 main functions.
1/ comparison on paper/computer programs, if the bc 's for both bullets are derived by the same process( not very often the case). But they do have a use for comparison.
2/ As a starting point on the range, for example if you have worked a spreadsheet for the newest 30 cal swizzlestick super master smasher and sighted in a 300 yds point of aim/ point of impact and moved back to the 600 yd line.The spreadsheet shows you are 4.5 moa low here, you would be silly to start at a different sight setting, unless of course you are really a sharp stick in the eye, and a) carry a laptap and instruments for measurement of conditions and factor these in as well.
b) you are an experienced shooter and can make a really good swag for conditions. swag= scientific wild
*ssed guess. for something like the changing light condition or a headwind, etc.
but of course you are still starting from your initial set of numbers from your ballistic data which is derived from your unverified bc.
another point to consider is the difference in the g1,g2 etc, I.E. drag function, which some ballistic programs make allowances for and some do not. Plus you about have to have a sliderule stuck in your ear to go along with your engineering degree to make a good use of that. which not knocking engineers at all, i wish i was that smart but I will settle for being good looking.
anyway for comparison purposes and as a starting point I love bc's but i whole heartedly agree with you that there comes a time when you just gotta get out there and work up your own zero's. I know there are many other factors to consider in shooting but I really don't feel like making a list cause sure as the world I would forget a factor or 2 or 3 and then be labeled as a stupid son of bourbon maker.
I like to discuss, not much on debate.
anyways that is my take on the matter.
Rifleman

[RBinAR]

edge said:

The B.C. is velocity dependent, and that velocity will most likely be different for PISTOL bullets vs RIFLE bullets.

edge.

To say I disagree a bit would not cause a fire storm would it? Ihope.

[edge]

RBinAR said:

To say I disagree a bit would not cause a fire storm would it? Ihope.

Could you elaborate?

I have seen a Sierra 0.308 180 gr. RN bullet with a S.D. of 0.271 with the following B.C.s:
0.240 @ 2800 fps
0.280 @ 2200 fps

Clearly the "shape" does not change :-) However the launch velocity will determine the "bow shock wave" and the degree of air compression. The Drag curve is continuous at supersonic velocities but you need a starting point from which to start your calculations.

edge.

[RBinAR]

I will try to elaborate but I may simply sound like a man with an incomplete understanding because that’s what I am. What you say is correct and incorrect depending on your point of view.

If you are trying to figure a path of motion for a bullet such as a modern hunting bullet then the BC does have to be adjusted for change in speed (but there are other ways) in order to provide an accurate approximation of motion. Typically this change is biggest when moving very fast or slow.

On the other hand if you are using a bullet that is the same shape (for the caliber) as was used in forming the motion model then one number will serve within any range the standard bullet was tested at. What causes the difference between our modern bullets and the base model is the model was conceived with a cannon shell as the standard. That is not at all like most modern bullets. Changes made in BC are not for effects of speed but an allowing for the fact the bullets compared are not the same shape.

As I said Sierra’s method of dealing with this works for different shapes of bullet, but it is a brute force approach (to me). I like but don’t have the math skills to recommend a method that accounts for the shape difference rather than changing BC in flight. ;D

[edge]

RBinAR said:

SNIP

As I said Sierra’s method of dealing with this works for different shapes of bullet, but it is a brute force approach (to me). I like but don’t have the math skills to recommend a method that accounts for the shape difference rather than changing BC in flight. ;D

Unless I don't understand what Sierra is showing, I don't think that they are saying to change the B.C. "IN FLIGHT", but rather at a velocity of "x" use this STARTING B.C.

The Drag shape should be fairly parabolic, so you need to figure out a starting point. If the Drag function was linear, then the velocity would not matter and the B.C. would be constant throughout.
I think that it is similar to the velocity of a falling body due to gravity(in a vacuum), if you don't know how long it has been falling then you can't calculate distance or velocity.

edge.

[RBinAR]

8-)Oh more math OH BOY! I don't know how to explain this best but let me ask, was not the drag function on the model bullet non-linear also? Do you feel that recording the speed of a model bullet would some how not account for the fact it is encountering the same varing effects of drag.

No it's quite plain a modeled bullet of the same shape would encounter the same effects. Those effects would be at different ranges because one bullet has a higher BC and will lose speed slower. But the effect is the same at some range.

The software that does the computations for the system like Sierra's simply does this. You give it a starting velocity. It picks a BC for that speed. When it reaches a certain lower speed then it assigns another BC. The process repeats till maximum range is reached.
All the rest of the math is the same as has been around since the early C1 cannon testing. The calculus has not changed nor will it ever. Excelleration and decelleration can be predicted in the same way it was 122 years ago.

For many years the G1 drag force model has been a projectile of 1" in diameter weighing 1 pound, OF THE SAME SHAPE, as the compared bullet. The shape causes the difference in BC not the drag. ;D

[RandyWakeman]

edge said:

The Drag shape should be fairly parabolic

Bullet Name Diameter (inches) Weight (grains) SectionalDensity BallisticCoefficients
.375 dia. 250 gr. SBT .375 250 .254

.353 @ 2600 fps and above

.371 between 2600 and 2250 fps

.375 between 2250 and 1800 fps

.363 @ 1800 fps and below

One might think that, but that isn't always the case. It can dance all over the place-- in the example above, the operating BC actually drops when the bullet drops below 1800 fps.

The Ingalls tables are flawed, and that is the short reason why today's bullet developers (and the US Military) use Doppler radar ranges to find out exactly what a specific projectile really does at a specific velocity / range.

[edge]

Randy,

If I had written the Coefficient of Drag is parabolic would that make you happier?

I would say that the B.C. Does NOT change, BUT it varies from the G1 Tables, so to bring the two into line you "fudge" the numbers for a better "curve fit"

edge.

[RandyWakeman]

edge said:

Randy,

If I had written the Coefficient of Drag is parabolic would that make you happier?

I'm not "unhappy." BC's are just numbers, and with rare exception-- bad numbers.

When it comes to Barnes, Hornady, and several other muzzleloading bullet makers-- they have been unable to state the basics of where their BC's come from: atmosphere, range, muzzle velocity. If they did, at least then those who want a vague idea of what to plug into their ballistics programs could have an accurate starting point.

The 250 gr. SST is published at .220, it becomes .240 when sold as a 250 gr. Shockwave. Amazing.

[edge]

RandyWakeman said:

SNIP

The 250 gr. SST is published at .220, it becomes .240 when sold as a 250 gr. Shockwave. Amazing.

Ahhhh, that is where you are mistaken.

The SST bullets are available @ Sea Level BUT the Shockwave bullets are sold @ 3000feet!

Same bullet, just a different perspective :-)

edge.

[RBinAR]

edge said:

Randy,

If I had written the Coefficient of Drag is parabolic would that make you happier?

I would say that the B.C. Does NOT change, BUT it varies from the G1 Tables, so to bring the two into line you "fudge" the numbers for a better "curve fit"

edge.

Well said. An understanding of C/D meaning that a given bullet conforms to the processes of math and nature is best.

The problem is that the bullet makers would have havoc in trying get the public to understand that the BC would change according to it's drag model. The demands of the creator's vision of motion would mean that a BC and the D/C model it fits would have to be stated. Try explaing why a boattail spitzer and a lessor bullet would both have a similar BC because they should have different C/D models. Only bullets of similar shape could use the "easy" (but flawed) buy the biggest number fad so common today.