Seems like a read somewhere here or at longrangehunting last year some threads about true ballistic coef. vs. those published by the bullet manufacturer.

Will someone please tell me what the TRUE BC is for the following bullets?:

.270:

140 Nos Accub.
130 TSX
150 Nos Btip
130 Nos Btip
130 Swift Scirocco

.30 cal:

165 Swift Scirocco
180 Swift Scirocco
150 S. Scirocco

168 TSX
180 TSX
200 Nos. Accub.
165 Nos. BTip
180 Nos. BTip

7mm:

150 Swift Scirocco
160 Nos. Accub.

I know I listed a lot but someone who has done extensive tests has posted some before, I just cannot remember where.

Thanks!

Doc, there is no answer for your question. BC changes with velocity, and atmospheric conditions influence it as well. Now that I consider it, everything that influences a bullet's flight has an effect if you want to get right down to particulars. Go with the factory published BC, it's a good starting point. If you have the time and equipment you may fine tune the number, the LRH crowd can assist you with the project insofar as what is needed. None of the bullets you list are serious contenders for extreme long range work in any case, and I don't mean that as a put down. The 200 AB and 180 BT are getting close insofar as BC is concerned. I'm thinking 1000 yards plus when I hear "long range", don't know about you.

I think the info you're looking for is at LRH.

http://www.uslink.net/~tom1/calcbc/calcbc.htm

Compare the chart above to the published data.

http://www.steyrscout.org/ballisti.htm

I think that many of Doc's bullets are "long range" bullets!

Thanks. Long range to me is 450-700.

In the rarest of situations would I ever shoot beyond 500. Even then, I wouldn't do it unless my rig and hunting conditions were as close to perfect as possible.

quote:

Originally posted by DigitalDan:
Doc, there is no answer for your question. BC changes with velocity, and atmospheric conditions influence it as well. Now that I consider it, everything that influences a bullet's flight has an effect if you want to get right down to particulars. Go with the factory published BC, it's a good starting point. ...

Hey Doc, I agree with DD. The numbers that Don provided are as good of a starting point as any.

Due to the changing BC, it is just one of the reasons a person ALWAYS wants to make their own Drop Chart for the distances they intend to take shots by actually shooting at those distances and measuring the real amount of drop.

If a preson simply thinks of BC as an approximate value instead of as an exact value, it will serve them better over the years. Nothing wrong at all about running the figures through a Ballistics Program to get "Approximate Drops". People that claim the Ballistic Programs are always right on the nose simply don't have enough Trigger Time to have seen the variance.

There are some freeware ballistic programs as well as ones costing money that allow you to input your data, range,muzzle velocity, atmospheric, humidity, manufacturer BC, barrel length etc and it spits out the actual BC and the drops for your various ranges.

Takes some research and trials to find the best program, but it is a lot simpler than doing it with a slide rule, calculator a pen and a lot of paper

Some computer software comes very close to predicting "true" B.C. However, I agree with HotCore and Digital Dan.

In my experience the only way to get actual true B.C. is to record the load, muzzle velocity, temp, humidity, etc., then actually fire rounds at the distance over which you need to know the B.C. From the drop over that distance, you can calculate the "true" B.C.

Even then, what you actually know is that using that load, to produce that muzzle velocity with that bullet, at those atmospheric conditions of temp, humidity, etc., you can expect the bullet to act as if its B.C. was whatever you calculated.

In sum, it is a circular logic...actual drop can be used to determine the actual average B.C. throughout the trip. With the actual average B.C, you can then (surprise!) predict actual drop (and wind deflection) at that range.

The only other real use of that B.C. info is to make close "guesses" of drop (or wind deflection) at other relatively close to the same ranges, or in roughly but not exactly similar atmospheric conditions, at approximately similar velocities. But even then those guesses won't be exactly correct except by serendipitous luck.

Like accuracy itself, what is an adequately determined B.C. depends on how big the object is at the range where you need to hit it.

Well, the reason I brought it up is sometime last year I read somewhere where an experienced shooter had been running some software for BC estimates.

His conclusions were fairly different than those of manufacturers.

I guess another way to ask the question is given the identical circumstances of velocity, temp., humidity, bbl length, etc.

Which bullets have the very best BC? I'm truly most interested in the TSX, Accubond, and Scirocco. I already know the BTip shoots real well, and with some of my loads, does not drop much at all in that first 300+ yards.

In the past I used the trajectory calculations and tables to get a rough idea of longer range trajectories,but after shooting the actual bullets at chronographed speeds,I found significant differences between calculations,tables and the actual trajectory.As such I now rely on actually shooting each bullet at the various distances to determine the trajectory.If a person is going to shoot at a game animal at 500 yards,he should have at least practised shooting the given load at 500 yards.Relying on tables or calculations at that distance can easily result in misses or worse yet wounded animals.

For any shooting at longer ranges, of course ballistics programs are only to "get you on paper" and actual shooting must be done before one can count on where that bullet is going....

BUT! When the "garbage in" (inaccurate BC's, velocity "estimates," no compensation for conditions, etc) is kept to a minimum, it can be quite amazing how little garbage comes out. They are only as good as the guy inputing the data. "Huge" differences will be due to an input error.

Doc, here's a test done by Rick Jamison that includes those bullets:



Unfortunately those aren't corrected to standard conditions so the absolute value of the numbers may not mean much. What does mean something is their relative values, comparing one bullet to the next.

Some like to exaggerate how the flutter of a butterfly's wing in the next county can skew BC data to the point it is meaningless...but this is usually due to a lack of scientific method on their part. Yes, there will be some variance rifle to rifle, condition to condition between the bullets.

BUT! Anybody who thinks a bullet on the bottom of the chart is going to magically jump to the top of the chart over other bullets and visa versa in his rile and his conditions just because he wants it to is dreaming.

quote:

Originally posted by Doc:
Well, the reason I brought it up is sometime last year I read somewhere where an experienced shooter had been running some software for BC estimates. His conclusions were fairly different than those of manufacturers.

Yes, this is somewhat of a Standard Assignment each 3-4 years with the old Gun Rags.

quote:

Which bullets have the very best BC? I'm truly most interested in the TSX, Accubond, and Scirocco. I already know the BTip shoots real well, and with some of my loads, does not drop much at all in that first 300+ yards.

Hey Doc, You just mentioned "that first 300+ yards" as the distance of importance.

That being the situation, inside 400-500yds B.C. doesn’t mean beans unless the person is attempting to use too Light of a Bullet Weight or too fragile of a Design for the task at hand. You simply pick the bullet you want to use and shoot it enough to become familiar with it's trajectory. Even a good old Standard Grade 165gr-180gr "Round Nose" Hornady, Remington, Sierra, Speer, or Winchester bullet will work great at typical 30-06 velocities inside your 300+ yard limit.

It is fun to watch the “discussions†about Bullet Z being better because it’s B.C. is 0.500 and Bullet Y is only 0.400 (or even 0.250), but the reality is that it just doesn’t matter up close.
---

I’d recommend you rate your bullet selection by Design and then by whatever other criteria you believe is important. Kind of a modification of determining what the “Natural Bullet Weight†is for your cartridge and hunting conditions.

For example, if your shots will all be 400-500yds or less, perhaps you would rate them in this order due to “Penetration Potentialâ€:
1. TSX
2. Accubond
3. Scirocco

But if you plan to shoot beyond that distance, then the “Expansion Potential†might be more important to you and the list might read:
1. BTip
2. Scirocco
3. Accubond

And of course, you can’t overlook “Accuracyâ€, so after shooting them, the list beyond 500yds may look like:
1. Accubond
2. BTip
3. TSX
4. Scirocco
Or in some other order.

But once you mentioned 300yds, as long as you use enough "Bullet Weight", the Standard Bullets will work just fine.

Nothing at all wrong with using the Premium Bullets you listed, and any of them will work inside 300yds too. At that distance though, you need not concern yourself with B.C.

Best of luck to you.

Excellent post Hotcore--very helpful!

friar

I agree with much of what Hotcore said, but personally I'd reduce the 500 mark to 300. By only 300 yds, when a "typical" 180 has lost about 600 fps of its muzzle velocity, I'm less worried about ultimate toughness of the bullet and more worried about accuracy at that range so it can be placed properly.

My opinions--accuracy of the bullet may ultimately have a big impact on bc. An accurate bullet with a tight spiral is gonna keep it's bc much better than one wobbling through the air. There was an article recently where they were testing round nose, match king and regular spitzer bullets. The round nose was very accurate in this particular gun and landed surprisingly close to the match king in drop at (I believe) 300 yds.
As others have said it would be best to test all the way to your intended hunting ranges. I've found ballistic charts with manufacturers bc's to be pretty darn close but I don't shoot past 300 yds. I've read posts from other people that say the coefficients seem pretty good till they start shooting at 500-700 yds and then the drop seems excessive in relation to listed bc's.
BOTTOM LINE IMHO--you gotta see if it's accurate all the way to the intended range and when you know that for sure you will know how weak the bc is...........if you haven't checked the accuracy you shouldn't be shooting out there at long range.

Well, I found the bullets I'll most likely use because of their design, kill worthiness, accuracy and general BC. They are bonded hollow points with low drag boat tail design:

wildcat bullets

I'm currently discussing with a Kirby Allen the construction of a 270 Allen Mag. Here's a comparison:

270 Win.........3100 fps w/ 130 gr BT
270 Allen Mag...3400 fps w/ 169.5 gr ULD
7mm Rem Mag.....3350 fps w/ 140 gr BST

Here's the bullet compared to btip:


Here's the cartridge (center):


BC: 270
169.5 gr ULD RBBT Wildcat BC 0.750

Cartridge is based on a 7 RUM I think. Barrel will be 1-8" twist for stabilization.

Hey Doc, I'm not familiar with that bullet at all. Looks like quite a Cartridge though.

One thing I would recommend you do is make sure he has good Load Data for it prior to jumping on. In the past few years I've seen a number of posts from folks who have purchased a Wildcat and really have no idea where to start loading or which Powder to try. The Ballistics Software Programs can "help" get you started, but there is nothing like good Data from an "experienced source".

Do you have any specific new Game animals in mind for the new Wildcat, or will it simply be used in place of your current 30-06?
Have you encountered a "field" situation where the new rifle would be a significant advantage over the old rifle?
Will you be using a 28" barrel?
What Powder does it use?
What kind of Scope will you put on it?
---

By the way, I've no argument with you folks that mentioned 300yds as the distance where B.C. doesn't make a quack. For a lot of years I used regular old 165gr RNs in 308Wins and 30-06s at 400-500yds(and of course a lot closer), so that is why I used those numbers.

The older I get, the closer I like them!

From Kirby:

Comparing apples to apples, the 270 Allen Mag will easily top 3850 fps with a 130 gr Ballistic Tip. Of course this is out of a 30" barrel but even given equal barrel lengths the Allen Mag will top the Win by +600 fps easily.

The 270 Allen Mag is based on a full length 7mm RUM case with the shoulder angle increased and body taper reduced to a very minimum. Case capacity of the 7mm RUM filled to the mouth with 8700 ball powder is 117 gr compared to 126 gr for the 270 Allen Mag.

The 270 Allen Mag capacity is slightly more then the 7.21 Firebird from Lazzeroni but it is able to be easily chambered in rifles such as the Rem 700 where as the Firebird is more difficult to squeeze into this size of receiver. It can certainly be done but at more expense then the 270 Allen Mag.

Cases are easy to form, run 7mm RUM cases through a 270 Allen Mag FL sizing die, prime, load, fireform, trim to length and your ready for serious performance.

The Allen Magnum rounds were designed for chambering in my Extreme Sporter rifles with barrel length of 28 to 30" and finished rifle weights ranging from 8.5 lbs to 11 lbs. They are also at home in heavier rifles as well but the goal was to offer the extreme in performance in a portable package and they have performed very well at that.

...That said, if you use the 169.5 gr ULD RBBT I would recommend you getting ahold of Jeff Bartlett at http://www.gibrass.com and order in some WC872 powder. This is GREAT powder for the 270 Allen Mag with the +150 gr bullet weights.


Good Shooting!!

Kirby Allen(50)

Just whipped this thru a program I have access to :

MV 3400 fps

BC .750 temp +59 f Latitude 40.0 alt 1000 ft

Air pressure 28.5 psi Humidity 78%

Effective BC .778

Second time with some changes

MV 3400 fps

BC .750 temp -10 Lat 40.0 alt 1000 ft

AP 28.5 psi Humidity 45%

Effective BC .671

I didn't bother changing the second one completely to actual conditions, just the temp and humidity to show how a relatively minor change can affect BC and how this could play out at longer ranges.

Hey thanks! Even a BC of .6 is awsome.

HotCore: I already took care of all the issues you brought up about load data, powder, etc. But thanks for the reminder.

I'm usually pretty thorough with my list of questions on a new topic to me.

Hey Maltese, will you shoot that humidity down to about 15% and temp to 30 degrees?

Here you go:

BC .750 with 15% humidity and 30 f

Effective BC .731

If you know the altitude and general air pressure it will change the numbers slightly.

Great, thanks.

glad I could help

quote:

Originally posted by Hot Core:
...Do you have any specific new Game animals in mind for the new Wildcat, or will it simply be used in place of your current 30-06?
Have you encountered a "field" situation where the new rifle would be a significant advantage over the old rifle?
What kind of Scope will you put on it?...

Hey Doc, Nice response from Mr. Allen.

How `bout these questions?

quote:

Originally posted by Hot Core:

quote:

Originally posted by Hot Core:
...Do you have any specific new Game animals in mind for the new Wildcat, or will it simply be used in place of your current 30-06?
Have you encountered a "field" situation where the new rifle would be a significant advantage over the old rifle?
What kind of Scope will you put on it?...

Hey Doc, Nice response from Mr. Allen.

How `bout these questions?

Sorry, I got a bit busy. No new game animals, just different terrain. Most definitely encountered several field situations where new rifle will make substantial difference.

Weaver Tactical.

quote:

Originally posted by Doc:
... Most definitely encountered several field situations where new rifle will make substantial difference.

Weaver Tactical.

Hey Doc, I know what you mean about those long fields.

Any particular reason you are interested in the Wildcat over say a 257WbyMag, 7mmRum, 300WbyMag or a 300RUM? Don't mistake that as arguing with you, cause I've been through Wildcats myself and they can be interesting. Just wondering why you would want to go with one over a Standard cartridge.

I've seen a lot of folks speak highly of the new Weaver Scopes - all models.

quote:

Originally posted by Doc:
Will someone please tell me what the TRUE BC is for the following bullets?:

I recently tested three of them over the Oehler at 5 and 205 yds. Not an especially sophisticated test and a small sample size so don't put faith in these numbers down to the last .001 or anything, but they are enough to give me a pretty good idea.

180 TSX measured .411
180 Scirocco measured .539
200 AccuBond .550

All numbers corrected to ICAO.

Like I said, I'd expect the averages to shift a little had I done 20-shot strings, etc. The Scirocco launched at the same velocity put about 100 fps on the TSX at only 200 yds at 4400 ft altitude (the difference would be greater closer to sea level).

FWIW, there you go.

Kinda nice to see an interesting thread w/o all the usual blowtorch opinions. And that is just my opinion.

Doc, not sure if your source is the same, but there was a fella here abouts that I haven't heard from in awhile that was planning to launch something akin to the .270 you speak of, .257, .270 and IIRC a 7mm as well. He was going to do something novel with the .257 in that he was planning bullets in the weight range of 140-150 grains if memory serves. Don't recall his handle at the moment but his MO sounds similar to the cartridge you're speaking of. Always thought the 1/4 bore would be a grand(er) caliber with a bit heavier throw weight.

Well, have fun, good luck!