Is this a typo?

[slophish]

If you go to sierra's homepage you will see a .338 250 gr matchking with a sectional density of .313. My understanding of bc is, it goes up corresponding to velocity. Am I mistaken?

According to their site it actually goes down? I've read they ran rounds accrossed radar, if this is true maybe it gives merit to triggerfiftys assumption that bullets fired faster slow down faster?

Anyways here are the numbers,
.587 2150fps and above
.606 2150-1700
.576 1700-1400
.484 1400 and below
I have not found this on other rounds. Just curious what you all think?

 

[Fiftydriver]

If you look at the Sierra listings of their projected BCs for their line of bullets, you will notice that some bullets have a drop in BC as they slow down, others will have an increase in BC as they slow. Still others will increase in BC to a certain point and then taper off just as you see with the example you list.

I have found that as most bullets approach the lower limits of super sonic velocity, they tend to become unstable. This instablity will translate into much lower BC because the bullet can not travel as efficently through the air because it is not fully stablized.

As a result it decelorates quicker and is blown off by the wind more.

This tends to be the case with most bullets.

Personally, I see nothing here that would make me agree with Triggerfifty that a bullet launched at higher velocity will decelorate faster then a bullet fired at lower velocity.

We had big debate over that and in my opinion a quality explination for his theory was never offered. If you take two bullets of identical design and weight and BC and launch one at 3500 fps and the other at 3300 fps, The faster starting bullet will always be faster down range.

I have yet to ever hear anything that disproves this.

Simply put, the BC of a bullet is continually changing as the bullet travels through its trajectory and velocity range. This change will be unique in most cases to each bullet design.

Just my opinion.

Kirby Allen(50)

 

[Dzaw]

velocity equilizations

Yes, a bullet that is faster at launch will be faster downrange

Yes, a bullet at a higher speed will decelerate faster.

Both are true. These are not mutually exclusive facts. Examine the facts.

A bullet lauched at 3500 FPS with a given BC will lose 100 FPS in a given distance.

That same bullet lauched at 3200 FPS will lose 100 FPS over a longer distance.

However, when the first bullet decelerates to 3200, it will behave exactly as the second bullet did from the muzzle, losing its next 100 fps over the same distance the second bullet lost its first 100 fps.

What we have is called the law of decreasing returns. As muzzle velocity increase, velocity at range increases, but at smaller and smaller amounts. Not until the speed of light in a vacuum is reachd do we see no returns. Basically, the return on increased muzzle velocity does decrease the more velocity you pile on, but that return will only approach zero. You will always get an increased velocity at range (as it is impossible to launch a solid in an atmosphere at the speed of light in a vacuum) but those increases in velocity at range will be smaller. At some point (we havn't even begun to approach that point BTW) the increases will become purely academic and ballistically unimportant.

say, for example, at a given range the bullet launched at 3000 fps is now going an even 2000 fps.

increase velocity to 3500 fps, at the same range that bullet will now be going 2400 fps. Noticeably faster, but not the full 500 FPS faster. Increase muzzle velocity again, to a hyper 4000 fps. At our given range, velocity is now 2700 fps. Still noticeably faster, but the increase is less still. following this pattern (dependant on BC) 4500FPS gives us 2900 at range. 5000 FPS gives us 3000 FPS at range, 5500 would give us, say, 3075, then 6000 would give us 3125, and so on and so forth. Never will we see a point where increase muzzle velocity means no increase in at range velocity, but at some point the 1 or 2 fps gained will be ballistically negligible. This example isn't exact, but it displays the principal in a succinct fasion.

I love calculus and physics!

 

[NYLES]

Re: velocity equilizations

No way! A and B Can equal Y at X.

A and B will never cross line Y at the same point(X).

SLOPISH,
What is the BC at 2150? 587 or 606 ?

 

[Dzaw]

Re: velocity equilizations

A and B will never cross line Y at the same point(X).


Exactly!

The point at which they cross line y will grow closer and closer together, but will never actually be the same point.

The difference APPROACHES zero.

That is, of course until you get within .01% of the speed of light in a vacuum, at which point Einsteinian physics and Euclidian math break down and becomes unreliable... Buth I don't think that's a problem we're likely to encounter any time soon ;>)

 

[NYLES]

Re: velocity equilizations

I thought that is what you was trying to say. Still not sure that the decelleration of the faster bullet happens any faster than the the other.
Dont have any graph paper to draw it out on!

This is in the near future Kirby is building a new ray gun as we speak! /ubbthreads/images/graemlins/grin.gif

 

[Buffalobob]

Re: velocity equilizations

I was reading a website last night about a guy testing the theory that a subsonic 22 LR bullet would not be disrupted by the transition and would carry more velocity to a 100 yard silloutte traget than the supersonic rounds which had to go through the transition.

According to his chronograph the supersonic rounds won the race and were still faster than the subsonic even after the transition. This is of interest if you try to shoot ground hogs at several hundred yards with a 22 LR. "Try" being the word that applies to my efforts. /ubbthreads/images/graemlins/confused.gif

 

[NYLES]

Re: velocity equilizations

We can control X, if we choose X as zero.

That is what our real world goal is. Finding X.
With a varible Y (distance).

So if we define X and Y.......B(3300) and A(3000) we simply gave B a 100yd head start.

Its amazing how huge a 300fps advantage is! /ubbthreads/images/graemlins/grin.gif

 

[slophish]

Re: velocity equilizations

Thanks for the replies. Nyles check out sierras website for conformation of those numbers, and you'll see what I mean. Dzaw, I understand the law of diminishing returns, and what you say makes perfect sense. Just trying to wade through those numbers. Fifty I agree with you, as it only makes sense. However- when you run exbal to extreme velocities with different bullets to extreme ranges all the numbers catch up to each other. I cant remember the exact rounds I used, I think .338 am-7mm am- and 416 barret caught up to each other at 3000 yds. I'll try to do it again(it was a while ago). That may have been what triggerfifty was trying to say.

I would like to relearn bc as cd. According to JBMs website this is more reliable. Shoot I just read mccoys book 6 months ago, their is alot to this stuff and I know very little. One thing for sure the math is intense and god gave me an old public school apple computer for a brain to figure it out.
Thanks.

 

[Jeff In TX]

No it\'s not a typo

I'm going to jump into this one with both feet...**** why can't I leave well enough alone!

IMHO, what the Sierra ballistic engineers put into their ballistic calculator is the wrong way to calculate ballistics. First they started with a G1 ballistic model by a Russian Col Ingalls Mayevski that is well over a hundred years old and is based on a 1", one pound round nose projectile. What a great foundation for to calculate today's modern flat base spire point, boat tail and VLD type bullets. The other reason they chose the G1 ballistic model is because it yields higher BC's for bullets. The theory is, the higher the BC the more bullets we'll sell.

Anyhow to get around the short comings of this century old calculation, they had to learn to massage that ballistic model to get better long distance accuracy out of their program. They did this by using multiple BC's that can go up and down as the velocity decreases.

The US Army at the Aberdeen proving grounds have mathematically worked out more efficient ballistic models which don't use G1 BC's for bullets. CD's are much more accurate, but having said that for small arms the G5 (standard boat tail), G6 (flat base Spire point), and G7 (VLD) ballistic models are hands down more accurate than what Sierra is trying to push. Some of today's better ballistic programs such as the RSI Shooting lab support those other models.

Think about this, they are using the same ballistic model for any type of bullet. So all types of bullets no matter their design will have the same flight/ballistic characteristics…NOT!

A Sierra .308 175 grain BTHP has a published G1 BC of .505. The actual G5 BC for this bullet .316. Lower BC's don't sell well, but the mathematical calculations used for the G5 ballistic model are extremely accurate, a lot more so than that massaged G1 stuff they're putting out.

Off my soap box, now let the flood gates open…**** why couldn't I just have left well enough a lone???

 

[royinidaho]

Re: velocity equilizations

Anyone have an in with the Mythbusters guys??

 

[bailey1474]

Re: velocity equilizations

[ QUOTE ]
was reading a website last night about a guy testing the theory that a subsonic 22 LR bullet would not be disrupted by the transition and would carry more velocity to a 100 yard silloutte traget than the supersonic rounds which had to go through the transition.


[/ QUOTE ]

How about a link!!!

 

[ppro]

Re: velocity equilizations

Gosh
I thought everyone new that about 22 projectiles. /ubbthreads/images/graemlins/grin.gif

Law of diminishing returns (?) also applies here too.


Paul

 

[Jeff In TX]

Re: No it\'s not a typo

To clarify my original post about using the proper drag model to calculate your bullets external ballistic, I thought I use a graph which shows all the drag models.

My ballistic program will let me calculate the exact BC of the bullet I'm shooting in my gun. It will also let me take my results and input the results to see what ballistic model best matches my bullet. With a little reverse engineering, I've been able to get my program to match my actual results to 1000 yards with .5 moa. The best I could get it to match using the G1 drag model was around 2.5 moa at 1000 yards.

These results were for my .308 I took moose hunting in Alaska, not that I was going to be shooting 1000 yards. They were for the Barnes .168 gr triple shock bullet BTHP.

The first graph shows all of the different drag models with my Barnes .168 gr triple shock in the upper porting of the graph. The G1 drag model I have an arrow pointed at is the modified and massaged G1 drag model used by many ballistic programs.

I then moved the Barnes .168 gr triple shock down to see which drag model best matched that bullet. As you can see it was an almost exact fit to the G7 drag model for VLD bullets. But you can also see, if I was using the G1 drag model that Sierra and most of the ballistic programs are using my results would not be very accurate.