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I have read numerous posts about poor or unexpected performance regarding their bullets and I am coming to the realization that some of us are unaware of the importance sectional density in guilded lead bullets. What does Sectional Density mean to you? Captain Finlander | ||
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It means what i select different bullet weight for different caliber or animal. For example moose i use a bullet with a sd of at least .240 in a 30 cal. in 6,5mm i need a heavy bullet for extra force so sd is at least .287 (140gr) | |||
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Sectional density is just a comparison between a bullets mass and diameter. All bullets of a given caliber and mass will have the same sectional density. Two bullets of the same caliber and weight will have the same sectional density, but be put together in a differnet ways. Back in the day when all we had were cup and core bullets, it may of had some value, but in the modern age of bonded, partitioned, and tapered jacketed bullets, it's really all that helpful in bullet selection. | |||
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Sectional Density is no more than a simple math relationship of weight vs. diameter. Thus, SD means nothing to me. It's an obsolete ballistic term that never meant much and means much less today. Eighty years ago SD had some marginal significance. In those days of unjacketed lead or simple "cup and core" construction, a higher SD in a given diameter usually meant, or was supposed to mean, it would penatrate deeper simply because it was heaver. BUT, it assumes all bullets of a given weight in the same caliber will perform the same and they will not! A current 150 grain .30 cal bullet in spire point; hollow point, ballistic tip, full metal jacket, partition, monolithic, etc., has a SD of .226. All have the same SD but they sure won't penatrate the same in game! Thus, SD has been meaningless for a long time. | |||
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Here's a good illustration of sectional density. Get a ping pong ball and a golf ball and throw them as far as you can. | |||
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Yes, the number means less today than it did back in the day but when considering copper jacketed lead cored bullets sectional density does have a value. The bullets with larger sectional density numbers hold together better, penetrate deeper & delivering grater hydrostatic shock. The opposite can be expected from lower Sectional Density numbers. A 150 grain .308 sheds its mass proportionately quicker than a 150 grain .284. This is one of the primary reasons the smaller calibers can produce fantastic results. So using the same 150 grain bullet at within 100 fps difference a 7mm08 will out perform the 308. So you can expect better killing performance from the heavier bullet weights for a specific caliber. Obviously this is only in relationship to lead cored bullets and does't factor in the same using the new solid cored bullets designs like the Barnes. | |||
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The "Energy & Momentum in perspective" article is very interesting: http://www.riflemagazine.com/m...e/PDF/ri5partial.pdf | |||
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Interesting that there are such extreme opinions (i.e. from it is critical to it is irrelevant) one way or the other! To me it simply summarizes two pieces of information about a bullet - i.e. diameter and weight - in a single figure. When shooting an animal, there are really 3 distinct 'phases' to consider. They are 1. internal ballistics (i.e. from the point the rifle is fired to the point the bullet leaves the muzzle) 2. external ballistics (from the time the bullet has left the muzzle until it impacts the target) and 3. terminal ballistics (i.e. wound performance upon impact). SD enters into all of these to one degree or another. With respect to internal ballistics, lower SD is actually better, as given the same weight and pressure curve a lower SD bullet should accelerate more quickly. SD is perhaps most important with respect to external ballistics. It is actually the BC (ballistic coefficient) that goes into determining a bullet's trajectory, given it's muzzle velocity etc. However, SD is a key component in BC! In fact BC can be written as the product of SD and a factor based on the bullet 'shape'. So, given the same bullet 'shape', a higher SD bullet will have a higher BC, and therefore will shed velocity more slowly in flight. Finally, with respect to terminal ballistics, I believe it is here that the claim of SD being irrelevant is most often made. On the one hand, in theory a higher SD should mean greater penetration. However, that is only completely true for a 'solid', that does not expand at all. It is really bullet performance (along with velocity of course) that will have the greatest influence on this. Hunting bullets are typically designed to 'open', which means the frontal area is expanded and the SD is radically changed. Arguably, a bullet with a greater area (and therefore lower SD, given the same weight) has an advantage here. I tend to agree that velocity and bullet performance are what really count here, and SD does not have the same importance as perhaps it once did in this regard (again, unless you are firing solids that do not expand at all). | |||
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A .308, 150gr Barnes TSX and a .308 150gr Sierra Game King will both have the same SD. The Sierra will make it about 12 inches into a block of Gelitin, the TSX will make it over 24 inches. So, in the field, the fact that they have the same SD is meaningless. | |||
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Put me on the side of meaningless. Actually it's not.....but it isn't what it once was. Bonded bullets and partitions and monometals have changed the value of SD quite a bit. It may have value as a component of internal ballistics but as an indicator of terminal performance it's no longer of any value to me! /////////////////////////////////////////////////////////////////////////// "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill | |||
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While there are many technical aspects of SD, think of it as a relative measure of penetration capabilities across calibers but not across bullet construction types... For example 150 grn 277 reasonably approximates a 180 grn 308 of the same bullet construction as the SDs are reasonably close. but a .308 165 grn solid or barnes X is likely to out penetrate a 180 grn .308 of cup and core design. SD is neither meaningless or the holy grail Mike Legistine actu quod scripsi? Never under estimate the internet community's ability to reply to your post with their personal rant about their tangentially related, single occurrence issue.  What I have learned on AR, since 2001: 1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken. 2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps. 3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges. 4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down. 5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine. 6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle. 7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions. 8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA. 9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not. 10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact. 11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores. 12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 200 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence. 13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances. | |||
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[QUOTE]Originally posted by Mike_Dettorre: a .308 165 grn barnes X is likely to out penetrate a 180 grn .308 of cup and core design. Finn Aagaard had strong testimony to that fact . SD is neither meaning less or the holy grail[QUOTE] Agree.  210x (vs) 210NP | |||
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  Or to simply sum it up  | |||
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 Alf has the ability to make a simply discussion extremely difficult with sixteen sylable words used multiple times in succession! Hoisting the flag seems appropriate! /////////////////////////////////////////////////////////////////////////// "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill | |||
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Capt, That's true ONLY if they have the same construction; they do not. 150 gr. .30 cal bullets all have exactly the same SD. Try shooting a Ballistic Tip, a flat point, a partition, and a bonded core into gel at identical velocites; there will be quite a bit of difference. And note that those are all game bullets, specifically omitting monolithics, target bullets and full metal jackets which would have even greater penatration ablilties but identical SDs. Therefore SD predicts nothing that's valid, therefore SD is meaningless ... except in our heads. | |||
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SD is a primary measurement, but of only a trending incidence... bullets of the same caliber, and same construction, then the higher SD would tend to have a higher buller integrity ... however, its meaningless to compare a barnes tsx .308 to a woodliegh light for caliber .510 bullet .... or v-v ..
opinions vary band of bubbas and STC hunting Club Information on Ammoguide about the416AR, 458AR, 470AR, 500AR What is an AR round? Case Drawings 416-458-470AR and 500AR. 476AR, http://www.weaponsmith.com | |||
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Referring to expanding bullets and removing the myriad of variables previously mentioned. Given a KE target value of 4000 Ft lbs and a specific type of projectile (i.e. 338 caliber Nosler PT) 210 gr (SD .263) @ roughly 2925 FPS (4000ft-lb) 250 gr (SD .313) @ roughly 2700 FPS (4000ft-lb) You might theorize the 250 gr penetrating deeper if both projectiles were stabilized properly. Lets also remove some more variables (test impact medium being the same and the impact distance being equal). We now have control limits where we can compare how the effects of SD impact penetration in a specific medium. Control limits; 1)Bullet type, construction, and caliber 2)Kinetic Energy to target/impact 3)Test impact medium 4)Impact distance 5)Temperature (might change properties of test medium) 6)Projectile stabilization You might find some conclusive test data if you were to incorporate these limits in a test and find some results for yourself as to if SD plays a role in penetration. | |||
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Nice mushroom on the X bullet. I'm sure it made a large wound cavity. Personally, I like the looks of the partition myself. | |||
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Just to add some more BS (ballistic study   ) to the discussion, another critical 'variable' in your experiment would be bullet performance, i.e. expansion. If we were to consider only 'solids', i.e. eliminate expansion from consideration, then your experiment would be more straightforward. However, how useful would the results be in practice?Let us assume that the bullet loses no mass and expansion varies between 0% (no expansion) and 100% (fully 'opened' which we further assume doubles the area). Doubling the frontal area would in effect halve the SD. So while the bullets in your example may start with SD's of .263 and .313, expansion would result in a final effective SD of between .132 and .263 for the first and .157 and .313 for the second. Looked at from that perspective one can see that the difference in SD due to expansion is potentially much greater than the initial difference between the bullets. Add to that random loss of mass and the differences are potentially even greater. Further complicating matters, note that expansion would occur over time, and differences in velocity would potentially also affect the result. | |||
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The variables can be practically infinate working with softs. You comments regarding solids certainly cuts those variables significantly. I sent some 416 softs to Michael458 to do some testing in a controlled method (gr bullet, velocity) etc to compare some readily available softs in a controlled environment, controlled medium. All the 400 gr projectiles and the same SD except a 370gr NF. Our test incorporated Swift A Frames, NPT's, Barnes TSX's and NF softs. All penetrated within 2" of one another. I recall the NPT's edged the others by a inch or so. So there was no real difference. I would pick the one that shot best in my rifle. Most of the premium grade bullets these days are all very good. The NF (370 gr) penetrated as well as all the 400's. All retained 80-100% of their weight. | |||
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Great humor.....love it! /////////////////////////////////////////////////////////////////////////// "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill | |||
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 More pure created by a HUGE lack of knowledge. | |||
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Hot Core, I was meaning to ask you. Are you going to change your handle to Deep Curl? | |||
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LOL whatever. The pointy point of the bullet is always the leading edge of the bullet.....the presenting surface never changes....the position of the bullet in its ballistic arc is irrelevant because at any moment in time the bullet is heading in the direction the tip is pointing. Howard Moses Lake, Washington USA hwhomes@outlook.com | |||
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I will say this for ALF....he has the most magnificent collection of historic Mausers I've ever seen.....I wish he'd post more photos of them..... /////////////////////////////////////////////////////////////////////////// "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill | |||
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Sure I can buy that. Nothing is perfect, not the bullet nor the "spin" the rifling gives it. That however is not enough to be relevant and totally irrelevant to the use of SD to compare various weights and calibers and derive reasonable expectations of performance. Really don't think that is "angle of attack" which would indicate changes due to ballistic arc. Howard Moses Lake, Washington USA hwhomes@outlook.com | |||
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Ok Alf, I understand that as velocity approached the speed of light, mass increases. Now I've been accused of HotRodding my 7mm STW, but I've never been accused of shooting a bullet so fast it's SD changed. Now I admit shooting a 160gr bullet at 3500 fps is a little on the fast side, but I'm sure I gained more in penetration when I switched to a bonded bullet then I do from the change in mass for approaching the speed of light. | |||
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Is not the Sd of the expanding bullet in game the most relevant? and Sd would vary according to how the bullet behaved, ie; how much did it expand?, did it then reduce its dia.? how much weight did it retain?.... A bullet will impact with a certain Sd, then begin to reduce Sd as it expands, more so if it looses weight in the process, then it could begin to increase Sd if its dia. decreases through petal loss, then decrease Sd if the remaining shank hits something causing it to bulge/expand. | |||
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Yes, I am not arguing that fact and as you change the bullet type you change its performance, this is stating the obvious. It has to be assumed that your using the same bullet type in order to keep the playing field equal. Example: 130 gr. .277 vs 140 gr. .277 vs 150 gr. .277 Nosler Ballistic Tips or whatever. Terminal performance associated with sectional density will improve with the heavier bullet. Meaning the 150 gr. .277 should produce the optimum terminal performance on game over its lighter brethrin. If you change the game, IE: Pronghorn vs Mule Deer the added terminal performance benefits of the 150 would be beneficial for killing the Mule Deer but not necessary for killing the antelope. Are Mule deer killed with 130 grain bullets, of course they are but the 150 would do a better job, technically. To illustrate this I shot a piece of 3/8" steel plate with the 130 grain NBT and 150 NBT. The velocity varied but the energy was equal. The 150 grainer penetrated the plate but the 130 did not. This is Sectional density at work. In summation, lead cored bullets continue to expand, shedding mass while penetrating so the more elongated mass the bullet has to start with the longer it will stay together while penetrating. Of course Barnes solid core hollow points have altered the sectional density issue by providing consistent expansion with retained weight which is in stark contrast to the lead cored bullets that continue to shed weight as they expand. This partially levels the playing field for smaller bullets. Captain Finlander | |||
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Even though SD is the same for the above 2 bullets (Barnes-X vs a Nosler Partition) performance will differ, as one has lost its petals (first expansion of diameter, then petal loss that gives us weight reduction and then settling with a smaller frontal area to near original diameter), whereas the Nosler Partition bullet in this case expanded without petal loss but displays some weight loss (typically 35%). It stands to reason that the Barnes-X will outpenetrate the NP due to Mo/Xsa. SD is always at work as it has mass and a frontal surface area from the moment when the trigger is pulled till it comes to a stop in the animal or a tree beyond - in fact, even if it loses all its mass and shatter in tiny particles. Internal ballistics: SD of the bullet forms part of the equation in the "expansion ratio". External ballistics: SD is a component of BC Terminal ballistics: SD becomes dynamic at impact- its pristine SD will change. IF it expands, SD changes IF it looses weight, SD changes IF it expands and looses weight SD changes (rate of change is bound to differ) IF a non-deforming Solid tumbles its terminal SD changes. IF a non- deforming Solid stays point-on, SD is still at work Which ever way we look at it, SD is always at work. SD becomes dynamic at impact and here is the kicker ... the reason we prefer expanding bullets in the killing event in game is to make a bigger hole as the bullet passes through the heart (accelerate the bleeding to death) and this transpires into a bullet that has to decrease its pristine SD in doing its intended work - so terminal SD becomes less. However another consequence of expansion or lower SD if you will is decreased penetration. And this is why we need adequate momentum to overcome the resitance by virtue of of and expanding XSA for the desired penetration for a specific application and this is coupled to the CONSTRUCTION of the bullet, as we see right here between the X-bullet and the NP bullet. Warrior | |||
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 I have enough of the old Hot-Cor Bullets on the shelf to probably outlast whoever gets them when I'm gone. So, I'll probably stick with the tried an true - handle. The problem is that if I changed handles, I'm so amiable that no one would ever guess it was old Hot Core. ----- Been Testing some steel Peach cans with Pellets from an Air Rifle. Have two kinds that have enough "Sectional Density" and Velocity from the Storm XT to Enter and Exit the cans. I find it interesting that the can does not move when hit with these two Pellets, just a nice hole in and a BIG hole out. However, the SSPs(Super Sonic Pellets) only dented the can at 26yds and tend to shake the can. Thinking back on it, "perhaps" they got Catywhampus during the flight, which resulted in their S.D. getting all messed-up. | |||
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I'm stock piling 200 grain Hot Cors for my 338 Federal. They shoot great and I've not heard very good things about Fusions/Deep Curls on game larger than Deer. Supposedly they open too wide with their bonded petals and limit penetration. I've seen pics of their expanded bullets and they tend to balloon out when they mushroom. I'm sure they are great on deer. | |||
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Scott, in my experience, the 200gr Hot Cors don't open up enough on deer, not even out of a .338 Win Mag, when pushed to 3k fps. .338 hole going in, about a .340 hole going out. Even if you shoot through a deer the long way, they still don't expand much. 180gr BT is a much better deer bullet for the .338 Federal. | |||
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AS, I appreciate the feedback. I'm actually using the 338 Fed for a CXP3 round. I have 257 Roberts and a 6.5x55 for deer. | |||
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