Relationship between BC and terminal perfomance


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PonyKiller
June 27, 2013, 11:00 PM
Just a bit of curiosity to me I guess, being relatively new to hunting. Publicity, and propaganda aside, when bullet strikes flesh is there any real world correlation between terminal performance and BC, is it inversely proportional or more related to construction. I know SD has a good deal to do with BC, also the penetration. So is BC more of a sidebar to terminal performance, or is it a major factor.

I get a kick out of watching the slow motion gelatin tests, a 170 grn flat nose 30-30 leaves a totally different channel than does a 130grn 270 win even with similar sd.

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allaroundhunter
June 27, 2013, 11:19 PM
BC is more related to trajectory and bullet shape than terminal performance. I wouldn't take it into consideration for a hunting round unless you plan on shooting long range.

jmr40
June 28, 2013, 02:57 PM
I disagree. Bullet velocity can have a huge effect on terminal performance. Bullets with better BC's maintain velocity far better at longer ranges. And the difference show up sooner than many think. I'll use an example from a couple of guns and loads I actually use.

A 338-06 with a 200 gr Nosler Accubond has a BC of .414. and can be fired at about 2850 fps.

A 30-06, shooting the same 200 gr bullet has a BC of .588 and can be fired at only about 2700 fps.

At close range the 338-06 has 150 fps advantage and about 350 ft lbs of energy advantage. At about the 200 yard mark both have about the same speed and energy. That is not really long range. But at 500 yards the 30-06 with a much better BC, has a 150 fps speed advantage and about 250 ft lbs advantage in energy. Trajectory is only .2" different at 500 yards and within 1" at all other ranges. I haven't ran the numbers, but would think the 30-06 would also have the trajectory advantage at all ranges beyond 500 yards.

Bullets with better BC often have better sectional density as well. The 200 gr .308 Accubond will out penetrate the 200 gr .338 Accubond even at close range even though it starts out 150 fps slower.

Art Eatman
June 28, 2013, 03:36 PM
Looking at the proverbial "for all practical purposes", the vast majority of game animals are taken inside of 300 yards. For the whitetail deer, inside of 200 yards.

So, yeah, BC will make some amount of difference out in Ma Bell country, but that's outside normal parameters.

Inside of 300 yards? BC should be of no concern. Bullet construction is what makes the difference.

MCgunner
June 28, 2013, 04:24 PM
BC has a positive affect on game IF you can use it at long range. Bullets slow down less with higher BCs at a given initial velocity. Quicker time to distance also means less drop which gives for a longer point blank range which means you can shoot farther without hold over or with less hold over. Higher BCs are a good thing, but the guy that only hunts in the woods and can't see past 25 yards will never know the joys of a high BC. :D Out in the rockies or the flat desert country, a high BC is a good thing for the marksman that can use it.

Sectional Density is a number that directly affects how well a bullet will perform on game. It's got nothing to do with the BC, though.

natman
June 29, 2013, 04:28 AM
BC is SD * aerodynamic form factor. So SD has a direct impact on BC.

Expanding bullets change shape radically on impact, so it's hard to say how BC relates to terminal performance. I suppose at one time it could have been argued that "round nose bullets expand better than spitzers", but spitzers have gotten awfully good at expanding in recent years.

While BC doesn't have much DIRECT effect on terminal performance, it does have an effect on velocity, which in turn affects terminal performance.

41 Mag
June 29, 2013, 06:38 AM
There are several ways to look at this IMO. My first criteria when looking at a bullet, is construction. I feel that even the modest old fashioned cup and cores are for the most part a great bullet. I use the intended game as a figure into how I choose that particular bullet. I look at penetration combined with expansion first and worry about it getting there last. IF it shoots good in my rifle the getting there part will be on me anyway and all the added BC in the world won't make it any better.

While penetration combined with expansion is about the epitome of the Nosler Partition, I simply don't feel they are the best thing for every situation nor are they needed for 98% of what I hunt. The old reliable Rem CL will 99% of the time work just fine.

Most of the higher BC bullets nowadays are equipped with a hollow nose and plastic tip. This will add not only to the BC but also to the sectional density depending on how you look at it. In scientific terms, the longer the bullet the higher the SD and possibly even the BC. The BC part depends on the nose shape. A .308 180gr RN will never have the same BC as a sleek 180gr Berger spitzer BT, nor if measured in OA length to diameter the same SD, but in most cases driven to the same velocity will usually penetrate straight through what ever the intended target is. The Berger, and nothing against them and just used as an example, will usually initiate expansion right from the get go and once this starts to happen it usually happens fast and penetration can suffer due to it. It is simply the construction.

Same case can be made using two great Nosler bullets. Take the .308 150gr Solid Base and the 150gr Ballistic Tip. The BT is a bit longer, has a higher BC, but it will also expand more quickly and violently than the Solid Base. Construction is almost identical other than the bit of hollow nose and plastic tip in the BT. Either one however, will do a fine job on most game out to 5-600yds if put where they need to go. The kicker comes in at ranges from 0 - 50yds where the BT is more subject to blow a gaping entrance, and waste a lot of meat due to the rapid expansion depending on velocity.

As has been mentioned if your looking to shoot out to 5-800yds then look for a high BC bullet, it will help out with higher impact velocity/energy, flatter trajectory, and less wind drift. IF your hunting from 500yds and in, unless your shooting loads that start out at around 2750 fps or so, then your not really going to notice a hill of beans worth of difference unless your rifle simply prefers that particular design. Just keep in mind that with some brands that higher BC also comes with a thinner jacket, possibly hollow nose either tipped or not with plastic. I would prefer a lesser BC bullet with somewhat more controlled expansion to a higher BC with rapid expansion for hunting game any day, as a bone in the wrong place at the wrong time can really make a mess of things.

I am not saying that a LOT of the bullets nowadays are not great examples of technology, and improvements. But I will say that I see a LOT of it as I do the fishing lure market, at what point is it driven to catch the fellow in the store, verses the fish or game in the field. I work for top accuracy so I can put he bullet I choose where it needs to go, after that I trust the construction of that bullet to do the rest.

PonyKiller
June 29, 2013, 09:21 AM
Thanks guys, for feeding my curiosity. I'm trying to scrape up the money to get into reloading as a one armed hobby for the next year and this has been something that's interested me.

Looks like texas was well represented in the responses! I'm stuck in jersey for at least the next few years, and to an extent the idea of bc in my state is a fallacy. We are limited to slug guns, which the some in the state gov't will tell you that we are lucky they allow us to have that.. what a joke... subject of another post. Anything with the bc higher that a thrown brick is good here.

Next year after i'm all patched back up my father in law wants to take me hunting in the Upstate NY, so I've got some time to add to the arsenal, and or work with my 30-30, while not the poster child for high velocity, its reloadable, I have the brass, and capable. Though I would like to get something in 270-30-06 range one day.

Kachok
June 29, 2013, 02:07 PM
High BC bullets are slim, long and tapered, they don't start causing much soft tissue damage until they expand since they by design don't cause much disturbance in relation to their energy. In contrast a flat point expanding bullet creates a large amount of disturbance as it passes through the air and hence it makes for more damage early in the wound tract even before expansion. Flat point or round nose bullets offer a real world advantage at close range but as the ranges get longer the efficiency of high BC bullets is vastly superior.

MCgunner
June 29, 2013, 11:21 PM
BC is SD * aerodynamic form factor. So SD has a direct impact on BC.

Yes, SD is a component of BC, but the higher the SD, generally, the better will perform a conventional soft point bullet in flesh. One cannot make any correlation of terminal performance to BC as BC involves drag coeffient and can be higher even with the same SD.

Now we have all the magic bullets, though, controlled expansion stuff like the Partition which really relegates SD to insignificance concerning how a bullet will perform terminally. But, generally, in a conventional expanding bullet, the higher SD is a GOOD thing.

From Wiki

http://upload.wikimedia.org/math/0/5/d/05d8fadc3435124a541697a17692efb1.png

where:

BCPhysics = ballistic coefficient as used in physics and engineering
M = mass
A = cross-sectional area
Cd = drag coefficient
ρ (rho) = average density
l = body length

http://upload.wikimedia.org/math/e/e/7/ee7c0b6cf246391bc092f77f2992c85a.png


sd is the bullets or shells sectional density
F is weight of the bullet, kg, g or lb, gr
d2 is the bullet or shell diameter squared, m2 or in2
p is pressure


The sectional density of a projectile can be employed in two area of ballistics. Within external ballistics, when the sectional density of a projectile is divided by its form factor[disambiguation needed] it yields the projectile's ballistic coefficient.[4]The sectional density of a projectile can be employed in two area of ballistics. Within external ballistics, when the sectional density of a projectile is divided by its form factor[disambiguation needed] it yields the projectile's ballistic coefficient.

Lloyd Smale
June 30, 2013, 09:20 AM
Looking at the proverbial "for all practical purposes", the vast majority of game animals are taken inside of 300 yards. For the whitetail deer, inside of 200 yards.

So, yeah, BC will make some amount of difference out in Ma Bell country, but that's outside normal parameters.

Inside of 300 yards? BC should be of no concern. Bullet construction is what makes the difference

I agree with art. At normal (out to about 300 yards) deer hunting it doesnt matter much if your using a high bc match bullet or a round nosed bullet. Even out to 500 yards the super dupper high bc bullets dont show much improvement over a standard pointed softpoint bullet. Out past 500 yards and those bullets start showing gains. Im sure someone can post some technical examples of why im wrong. Keep in mind im talking real world differnce in the field on deer sized game.

MCgunner
June 30, 2013, 09:38 AM
Lloyd, only for cartridges like .243 or maybe even .250-3000 or .257 Roberts or .25-06 would I say you'd gain anything on DEER to 500 yards with a high BC bullet and that'd be more about retained energy than drop. One can compensate for the added drop of a flat based bullet if one is skilled, but drop below that 1000 ft lb level for deer and I'd begin to think the range limit for the cartridge/load had been exceeded.

I don't much care for round nose bullets. I had an old Spanish M1916 in 7x57 that would shoot nothing but the heavies due to fast 1:7 rifling. Only bullet I trusted in it for deer was a 175 grain Hornady RN. It was pretty worthless on paper past 250 yards. As I have better rifles, I never really warmed to that gun. I shoulda taken the scope off it and kept it just because, i guess. I paid a grand sum of 60 bucks for the rifle and the scope and mount set me back about another 80 for drilling/tapping and a cheap walmart 4x Tasco so I could at least play with it at the range. I sold it for what I had in it to a guy that wanted a rough and ready rifle for his boat. Round nose bullets work fine in brush and seem to always expand well do the the amount of lead that is exposed, but at the time, I figured I could fire the very same bullet in my 7 mag, just download it, and heck, the Savage was lighter than that pig of a military gun. I thought the Mauser kinda cool as it was short, but it was heavy.

I haven't bought a round nose bullet for loading since I got rid of that Mauser. I do shoot Game Kings, though. :D For a woods gun, now days, Ive taken to .50 caliber from a CVA inline. Hey, it's pre-expanded. :D

MCgunner
June 30, 2013, 09:46 AM
Oh, another example of a good BC bullet helping a more marginal cartridge....Hornady Leverlution in the .30-30. :D One can turn a lowly .30-30 into a 300 yard gun with the right bullet. I load the Nosler BT 150 grain in my .30-30 contender and it's a genuine 200 yard pistol. I had a Savage M340, got it in the late 60s, was crazy accurate with Sierra flat based 150 grain bullets. I didn't know what a boat tail was back then, nor BC for that matter, but had read about extending range with a spitzer bullet in the caliber. I took one deer with that rifle, kinda preferred my .257 Roberts. That deer was taken at about 80 yards. :rolleyes: LOL.

natman
June 30, 2013, 11:25 AM
Most of the higher BC bullets nowadays are equipped with a hollow nose and plastic tip. This will add not only to the BC but also to the sectional density depending on how you look at it. In scientific terms, the longer the bullet the higher the SD and possibly even the BC. The BC part depends on the nose shape. A .308 180gr RN will never have the same BC as a sleek 180gr Berger spitzer BT, nor if measured in OA length to diameter the same SD,

Sorry, but this is not how it works. SD is a function of only two things: mass and diameter. Length has nothing whatsoever to do with SD, although a heavier bullet of the same caliber and density will tend to be longer. A 180 grain .308 bullet has a given SD, no matter what its shape. If you want to argue this point, please find a formula for SD that says anything about length.

BC, on the other hand, depends on SD *and* shape, so a spitzer bullet will have a higher BC and will probably be longer than a round nose of the same weight and SD.

PonyKiller
July 3, 2013, 10:14 PM
thanks guys, for all the good info. So in the end as I gather here the effect SD has on terminal performance is the retention of energy, after that it's bullet construction and relying on the design operating in it's given speed range.

My old Winchester seems to like the flat nose federals, and the hornady leverevolutions. They group almost the same size, and are very close it poi. So when I start reloading it, in essence it won't much matter the BC since it's a mid range cartridge, for hunting anyway. It's when trying to eek out the last few yards of performance out of I is when it matters. At that point if two loads show similar accuracy the one with the higher BC is generally better if availability, and price are non factors. And i'm sure having a few accurate, suitable loads is always a good idea.

cowtownup
July 3, 2013, 11:12 PM
Good info here on BC and SD...


http://m.youtube.com/watch?v=RCu8a5MynwM

taliv
July 3, 2013, 11:53 PM
i don't think there's a mathematical relationship between BC and terminal performance. however, due to differing design goals and thus different design decisions as bullet makers optimize a bullet for either accuracy or terminal performance, tradeoffs are often made. thus, there is often something of an inverse relationship, meaning most good hunting bullets would make poor match bullets and most good match bullets make relatively poor hunting bullets.

there are of course some that compromise and do both passably well.

1858
July 13, 2013, 12:53 AM
I'm under the impression that PonyKiller's question was more along the lines of whether or not a high BC helps terminal performance once the bullet hits the intended target. As taliv pointed out, the features required to increase a bullet's BC typically work against the bullet's ability to expand in the target.

Consider a low BC 230gr .45 Auto JHP bullet moving at 800 fps. It can penetrate 13" to 15" in bare gelatin set 10 feet from the muzzle and expand to almost twice its original diameter exhibiting excellent terminal performance. A 300 AAC Blackout subsonic load shooting a 220 SMK with a relatively high BC (twice that of a 230gr .45 JHP) at 1,000 fps will have zero expansion and pass right through the same block of gelatin set 10 ft from the muzzle.

The best compromise these days for long range hunters is something like a Barnes TTSX bullet. The tip is discarded on impact to reveal a sizeable hollow point (with stress risers) in the ogive which gives the bullet a much better chance of expanding.

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