I’ve seen the 6.8 SPC ballistics gel pictures compared to the 5.56 ballistics gel pictures and read up on the history of the 6.8 SPC, but this has brought up a question which I can’t seem to find and answer to.
Is the diameter of the bullet or it’s mass more important in determining the fragmentation “pattern”? What I mean is assuming the same type of bullet would an 80gr 6.5mm/.257/.224 bullet leave a similar but smaller fragmentation pattern then an 80gr 6.8mm bullet, or would it be roughly the same?
I remember reading how the 7mm fragmented better then the 6.8 when they were developing the cartridge and how the 6.5 fragmented less, but I’m not sure if they used the same type of bullets (i.e. thin jacket partitioned) back when developing the cartridge, or even if they were the same weight. This also seems to be the problem when I see 5.56-6.8 comparisons, they are almost always using two different kinds of bullets and I suspect this is why even the light 6.8 has better barrier penetration then the 5.56.
I’m sure this has come up before but I don’t know what I’d search for to find the previous thread, sorry :sad:
I think what you’re asking about is sectional density, which is the bullet weight in pounds divided by the square of its diameter. This does have an effect on penetration, but there are really too many variables at play in terminal ballistics to nail the effects down to any one bullet attribute.
Besides the aspect of sectional density mentioned by the post prior to this, bullet construction will determine what the round does at/during impact.
Probably a good idea to review as many calibrated ordnance gelatin tests as possible, hopefully tests that subject the design in question to a number of factors (especially intervening barriers like soft/hard armor, clothing, various building materials etc.), and try to draw conclusions based upon the available test data.
Even then, the same design will likely produce a (sometimes surprisingly) varying range of results within a single test design depending upon the manufacturing process and varying QC/QA standards.
terminal ballistics is the point at which a bullet impacts an object. there are also two others…internal & external…what the bullet does inside the bore and once it exits the muzzle. external ballistics are more based towards a bullets flight path, bc, and sd. bc is a mesurment for lack of better term how stream-lined it is. a bullet with a higher bc will drop less and retain more energy and fps. sd is a measurment meant to be more for a bullets ability to penetrate. bullet constuction effect this in a major way tho. a high sd and thin jacket is not going to penetrate well.
back to more or less what your wanting to know about diameter and mass. a bullet with a bigger diameter is going to create a larger temporay cavity. when the bullet hits and begins to transfer it’s energy it’s gonna really stretch that muscle and tissue out causing more trauma. this is only true of a bullet moving at moderate fps. or else it will proly jst punch straight thru. light fast bullets that frag will create tons of damage also. heavier bullets with a bigger diameter and decent fps will transer energy better for better wound profiles. heavier bullets don’t decelerate as quickly because they have more mass…hence they retian more energy at longer ranges as compared to a 5.56. 5.56 will fizzle out faster because it does not have as much mass. eventually the air it’s cutting thru will slow it down.
today’s day in age bullet selection is more then likely gonna contribute the most to what ever your needing it for.
jst something else to throw in…the more fps you have the more energy you have…speed kills.
Thank you for the replies, but that’s not what I mean, let me clarify.
Ceteris paribus (same velocity, same bullet type) is it the diameter (5.56 mm, 6.5 mm, 6.8 mm, 7 mm) or how much mass is in the bullet that determines more how large the fragmentation pattern is.
I guess the second part could sort of be thought of as sectional density, but that’s a calculated aspect where I’m more concerned about the pure amount of mass capable of being thrown out from the upset point.
So I guess I could try stating the questions like this:
All else being equal including mass, would a 6.8mm bullet leave a noticeable larger permanent wound channel then a 5.56/6.5 bullet, or smaller then a 7/7.62 bullet?
All else being equal, does a higher mass/sectional density bullet leave a noticeably larger permanent wound then a less dense/less massive bullet.
yes. if everything is the same (weight & fps…bc and sd will def. be diff.) the bullet with a bigger diameter will leave a bigger hole. this is ofcourse if you take two bullets with the same constuction. it is arguable that a shorter, fater bullet will transfer energy better because it will expand faster, because it’s not as long and has a larger surface area. jst depends on the nature of the bullet.
Just to clarify, you mean a bigger permanent wound pattern, not just a generally bigger hole because I don’t need someone else to tell me a 12ga slug leaves a bigger hole then a .224 :laugh:
So within a short range of each variable, which one is more important? As in would a 100gr 7mm leave a bigger fragmentation pattern then a 110gr 6.8mm?
And finally I thought longer bullets fragmented at lower speeds and more violently as they yawed, you say a shorter faster bullet transfers more energy, but does it fragment better?
all else being equal, a larger bullet leaves a larger hole- the difference being measurable by the thousandth of an inch.
in other words, only on paper, and totally insignificantly. just like with pistol rounds, only much less so (since we’re generally talking .224-.30 diameters). size of bullet really doesn’t mean anything, which is to answer your question, and what i think a poster or two above was trying to get at.
what IS important are the factors you’re wanting to make equal- they’re not equal. different loads perform more or less. a 150gr+ non-fragmenting, non expanding .30 cal bullet will do substantially less damage than a fragmenting 55gr 5.56 load.
I suppose I’m not making myself clear, I’m only concerned with fragmenting bullets. Specifically I’m wondering if the diameter or the mass of the bullet is more important to how large the fragmentation pattern is.
Of course a heavier+wider bullet will leave a larger permanent wound channel if it frags compared to a lighter+smaller round, but would a heavier+small diameter round leave a bigger or smaller wound channel then a light+large diameter if both fragmented ideally.
i don’t think it’s really an answerable question, then. 5.56 and 7.62 loads cannot be the same weight and have the same diameter.
but i can say that an ideally-fragmenting 7.62 load is going to do more damage than an ideally-fragmenting load in 5.56- because its more massive- not necessarily because it’s larger. it’s the fact that it has more weight/energy- all those little pieces of fragmentation are going to be more massive/heavier and carrying through better than the 5.56 pieces. therefor it’ll rip more shit up.
here’s a link to hornady’s TAP digital catalog. you can compare the diff. between 6.8 and 5.56. 6.8 shows more damage. 6x45 may be a good build if your wanting something to bridge the gap. the heavier .224 bullets do some damage so 6mm should be even better…maybe even pretty close to 6.8. i’ve been tossing the idea around for a while now myself.
Thanks Country Boy, that’s kind of what this is all about, I’m trying to figure out what exactly causes the 6.8 SPC to fragment so well compared to other 5.56 alternatives like the 6x45 or 6.5x45/6.5 MPC, 6.5 Grendel, etc besides bullet choice.
The 6.5 MPC looks nice but I can’t figure out how JD gets his numbers. And even if the numbers are right there are no gel tests out.
Either way, this mostly an academic exercise. I’d just like to better understand the basic rules of why terminal bullets behave the way they do.
I don’t think diameter is a serious factor at all in terminal ballistics.
What matters here is how much energy a bullet has, and how it behaves when it hits flesh or ballistics gel.
We can say a football shaped 5.56mm round is not going to do much with its energy due to having a perfect center of gravity. The round will slip through the ballistics gel without much “tissue” disruption.
Alternatively, a typical soft point 5.56mm would behave in a way to cause significant injury compared to the former.
I want to also say that the more weight a bullet has for a fixed amount of energy, the more it can accomplish with that added mass.
*I’m not a ballistics expert by any means. Nor did I ever stay at a Holiday Inn.
your exactly right with that statement. a shorter fatter bullet will transfer it’s energy faster into a target. bigger diam. will expand more and the bigger frontal diameter of the bullet will also help transfer energy better…yeah it’s only a couple thousandths difference, but hey take it as you will. what matter most here is which bullet constuction you choose for the task at hand.
“As clearly illustrated in the relevant scientific literature over the past 20 years, kinetic energy or momentum transfer from a projectile to tissue is not a wounding mechanism.”
