You guys getting tired of newbie questions yet?? Been poring over the books again and its seems like to me that there is a , using the term loosly, core of relatively 'efficient' bullets in roughly the 6.5~ .308 range. Where you have relatively high bc and sd numbers. This 'efficiency ' seems to be most relavant to long range guns/cartridges. Say, shooting for consistency, with power past 250~300yds. It would seem to me that at less than 200yds some of these numbers would be of less signifigance. A 35 cal 250 grain slug moving 2500fps will stop large angry animals but has the bc of a barn door. Am I thinking somewhat close here?? Appreciate any comments.

Can think of BC as a shape factor...SD as a factor of weight and diameter. Two bullets, both 250gr. and .35cal, will have the same SD, but the BC can be widely different (Hornady's 250gr. RN has a BC of .271, the 250gr. Spitzer has a BC of .375, they both have a SD of .279).
Put a boat tail and a long hollow point on it like match bullets often have, and could praobly raise the BC into the low 400's.

Car anology:
Identical motor and frame (think of that as SD)...slap a jeep body on it, and a 'vet body on it (think the BC here), which will be going faster at the end of a quater mile?

Well, ombesb,
I think you've just progressed beyond the "newby" stage into advanded stuff that most shooters take a long time to comprehend. A bullet with a large SD will penetrate farther. A bullet with a high BC will penetrate farther thu the air. Increased SD generally improves the BC in a given caliber, but not always. But, you're right that it's most academic inside of 200 yards; you must have a very accurate rifle and there must be a REALLY big difference in BC between two bullets for it to become apparent in the randomness of trajectory. If you only have a two MOA rifle, you'll have a difficult time distinguishing the bullet that only drops 1.78" from the bullet that drops 1.80".
There is a balance of BC against muzzle speed. (Even tho it's standard practice to use the word "velocity" instead of "speed" I don't like to because "velocity" is a vector quantity, comprised of direction and speed.) A lighter (lower SD) bullet can be launched at a higher speed. The heavier (larger SD) bullet MAY (but not necessarily) eventually pass the lighter one but will probably do so at a distance beyond where I should be shooting a game animal.
Another thing, although BC is cited to three digits, only the most significant digit is accurate. The second-most significant digit is ballpark and the third digit is a wild guess. Nosler has admitted as much in their loading manual. Check out Sierra's loading manual because it has an extensive section on exterior ballistics. BC depends on lots of things besides just bullet shape. Measured BC is affected by rifling twist rate; above or below the ideal twist rate for that length of bullet will reduce its BC. BC is strongly affected by velocity. E.G., Sierra lists its .30-30 150-grain flatnose as .185 @ 2400 fps & above, .224 between 2400 and 1800 fps, and .265 below 1800 fps. Selecting a boat tailed bullet because its BC is .387 vs. the flat base's .383 seems silly to me! (Check it out, that's really the difference between the two 130-grain .277" Sierra bullets.)

That's enuf for now!

-91

That is a fine rendition of a ballistic report, 91 -

Agree completely with what you say. B.C's are fine for target shooters and those long distance plinkers, but for hunting purposes, SD's have much more meaning. I can jillflirt the BC of a given bullet just by up and down powder loadings. Can't do that with the SD.

I agree with the others for the most part, but in some instances, the higher the SD doesn't always equate with more penetration. Any two bullets of the same diameter AND same Construction that would appear to be true if pushed to like velocities.

However some of the monometal bullets seem to be re-writing the general penetration rules.

Also, if we have a 30-06 shooting 180 grain bullets at, say, 2700 fps, but one bullet is a Sierra MatchKing and the other bullet is a Nosler Partition, we have completely different ballistic coefficients and penetration will likely much different also. When comparing penetration qualities of different bullets of the same caliber and weight, different design characteristics and different metal properties will cause one bullet to penetrate less than another.

Don't think they rewrite the rules...they just apply them differently. Bullet expands..it gets wider and shorter...SD goes down, penetration slows then stops. One that expands early, becomes a lower SD bullet earlier...by the time it looks like a mini-pizza, the SD has evolved to a very low value.

What the new controled expasion bulets seem to do is to expand slower and later. Bullet stays long and narrow a bit longer during impact...so the SD doesn drop from rapid expansion at first contact.

Predicting penetration by SD may have some value in solids that doen't expand at all. Can be a guide line for bullets of equal construction. But comparing two bullets of different construction by SD isn't all that valuable.

BC is mostly shape related. Hornady 170gr. FN flat based bullet earns a BC of about .189. Hornady 168gr. HPBT Match bullet earns about .450. True, BC is changed by velocity, but in a given rifle caliber, can generally heave bullets of the same weight to ABOUT the same speed (are differences based on bearing area and OAL, but genrally not enough difference to have BC valuse change all that much).

Can think of BC as a shape factor...SD as a factor of weight and diameter. Two bullets, both 250gr. and .35cal, will have the same SD, but the BC can be widely different (Hornady's 250gr. RN has a BC of .271, the 250gr. Spitzer has a BC of .375, they both have a SD of .279).
Put a boat tail and a long hollow point on it like match bullets often have, and could praobly raise the BC into the low 400's.

Car anology:
Identical motor and frame (think of that as SD)...slap a jeep body on it, and a 'vet body on it (think the BC here), which will be going faster at the end of a quater mile?
Ribbonstone,
Thanks for the 'auto anology'
I've always had trouble understanding those terms.
Every little bit helps.
Frank

This all started when I was reading about the 35 Whelen and it being considered fair to good for all big game in North America , then crossing that with accounts of the 6.5x55 being used for elk and moose. Apples and oranges as as bullets and cartridges go. The little one has much higher bc and sd numbers but relys and works seemingly quite well with lower speeds not causing such violent or rapid expansion . Thanks for all the input.

Sorry for a little confusion there, I intentionally left out bullet contruction on purpose. One less variable to confuse the issue. Certainly didn't mean by not mentioning it that it was of no consequence.

Hey folks...good thread here. I was thinking about this and how it applied to my 6.5x55 Swede as well! OMBESB note. OK....Im also relatively new to this so here goes.....I should clarify that I understand the BC and SD of the bullets. I am in the process of loading 140 gr Barnes X that have GREAT numbers! Can any one set me at ease with the issue over using this on a bull moose? Will it create the same devastating terminal trauma as say a 30-06, 270 or 300 win mag? I hope that you can appreciate my "newbie" status...

Cris

Cris,

No issue with the load you mentioned and Bull Moose, I personnally think that it is more than adequate. It will be tough to practice with the X'er load, just because of the expense of those rounds, but I would make sure that it suits you on the range before you take it to the woods. X bullets can be particular about the rifle they are launched in, although I hear that is getting better.

As for your comparison, My opinion is that your performance will be roughly equal to the 270 with a similar bullet, shaded by the 06 to a certain degree, and the 300 will eclipse it noticably, providing all are shot with the same competence. A good SD makes this round penetrate more effectively then its numbers would suggest, but I don't think it has the gravity to make the swede the overwhelming choice.

The utility of the 6.5 swede is that is is generally accurate, with good manners off the shoulder, and so folks tend to shoot it better. If this is the situation in your case, it is the right selection. you have a 300 mag that you shoot just as well, it is a better tool for the job, this man's opinion.

For me personnally, I shoot my 270 more competently than my 6.5 swede, and my 30-06 and 35s almost as well. For me then, the swede would not be my selection.

Good hunting, kill a great big one, and tell us all about it.

Steve

K98 Might take a look at Handloader #228. (April) " Petite Power Loads for the 6.5" worth a look.

ombes,

BC is an indicater of how efficiently a bullet passes through the air. The higher the number, the more efficient a bullet is. The results are a higher retained velocity and a flater shooting bullet..

SD indicates the total mass of the bullet and has no bearing on the BC. If a bullet with a higher SD strikes an animal at the same angle and velocity as a bullet with a lower SD, all else being equal, the bullet with the higher SD will penetrate the deepest. This however, is dependent upon bullet construction. Good luck.

K98cris:

Haven't dfone much with the 6.5X55. HAve played with a 6.5Jap, 6.5RM, and a 6.5X57. The 140's will penetrate...the 160gr. Hornady RN will PENETRATE, but lacks the BC of the pointed slugs. PArt of the 160's penetration is the micro-tip of lead...not very much exposed and a stout jacket.