Recreation

Same Cartridge, Different Bullet Weights. Does It Matter?

Another fun discussion with a reader with some great questions and comments got me thinking again. As per usual, it made me realize that there are still many things for me to learn about when it comes to shooting sports. This time the question, in context of a cartridge comparison, was “would bullet weights/designs/manufactures alter these findings?”

Initially, I wanted to confidently answer with a “yes”. However, as I started to answer I realized I didn’t really know all the factors. I just new some general rules of thumb that I’ve gathered through anecdotal experience or repeated phrases from various people. I’ve started to find that several of the repeated phrases tend to be old wife tales also based on anecdotal experiences that tend to be more myth than fact. So, here we are.

As I started writing this, I hold the following statements as generally true:

  1. Faster moving projectiles have flatter trajectories.
  2. Heavier projectiles are less prone to wind drift.

I’m going to start exploring these generalizations by looking at a single rifle cartridge from a single product line offered with the same projectile type in different weights. I expect the generalizations to hold true, but I also hope to be able to learn (and consequently explain) what the difference in bullet weight means. Moreover, I hope to determine whether or not the weight difference matters. You may have to bear with me for several post as I have a feeling that the answers will vary as I explore different applications and platforms. For the purpose of this post, I’m looking at this through the perspective of long distance shooting applications.

As I’ve done in cartridge comparisons past, I’m going to look at Hornady’s Match product line. Yes, I like this product line. No, I’m not promoting it and don’t receive any compensation for promoting it (if I was). The main reason I’m using it is because they make the information easy to find. I’m going to specifically look at three 6.5mm Creedmoor (6.5 CM) product offerings from this line all using an ELD Match projectile.

Advertised Ballistics120 gr ELD Match140 gr ELD Match147 gr ELD Match
Sectional density.246.287.301
Ballistic coefficient.486 (G1)
.245 (G7)
.646 (G1)
.326 (G7)
.697 (G1)
.351 (G7)
Muzzle velocity2910 fps2710 fps2695 fps
Muzzle energy2256 ft/lb2283 ft/lb2370 ft/lb
Advertised ballistics for 6.5mm Creedmore Hornday Match

Based on the advertised data alone without using a ballistic calculator, I assume that the 120 grain load will have the flattest trajectory and the 147 grain load will have the least wind drift. However, I’m unsure about guessing which load has the longest effective range for hitting paper or steel targets at extended distances. But I’ll place a bet on the 140 load for the longest effective distance as it seems to me like it’s the most common projectile weight for the 6.5 CM cartridge in the market today.

Did I place a winning bet? Let’s take a look at velocity over extended ranges.

Velocity120 gr ELD Match140 gr ELD Match147 gr ELD Match
500 yards2028 fps2059 fps2090 fps
1000 yards1347 fps1516 fps1577 fps
1100 yards1245 fps1424 fps1487 fps
1150 yards1200 fps1380 fps1445 fps
1200 yards1159 fps1339 fps1404 fps
1300 yards1090 fps1262 fps1326 fps
1375 yards1048 fps1209 fps1273 fps
1400 yards1036 fps1193 fps1256 fps
1475 yards1001 fps1149 fps1208 fps
1500 yards991 fps1135 fps1193 fps
Velocity at extended ranges

Well, looks like I lost that bet. I’ve highlighter the longest entry in the velocity table where the velocity was above 1200 fps. Dipping below that point means the projectile will start crossing the transonic barrier and will begin to destabilize. That’s essentially the effective range of the projectile were one can assume consistent accuracy.

I was surprised by these findings. I didn’t want to place my bet on the 120 grain load because it’s BC was significantly lower compared to the other two loads. I had thought the difference in BC between the 140 grain and 147 grain loads was small enough that the 140 grain load with its larger initial muzzle velocity may edge out the 147 grain in terms of distance. I was wrong.

The data highlights how the BC also comes into play in terms of how fast it slows down a projectile. Even at the 500 yard marker the 120 grain is already traveling slower than the other two even though it started out as the fastest. By the same token, the 147 grain which started out as the slowest has slowed less than the other two loads.

Pretty cool. But let’s look at drop and see if my assumption about the 120 grain load being the flattest is true.

Drop120 gr ELD Match140 gr ELD Match147 gr ELD Match
500 yards48.9″53.1″52.7″
1000 yards320.6″316.8″308.8″
1100 yards422.3″408.5″396.4″
1150 yards481.3″460.8″445.9″
1200 yards546.3″517.5″499.9″
1300 yards696.3″645.8″620.9″
1375 yards827.7″756.4″724.4″
1400 yards875.4″796.1″761.6″
1475 yards1031.1″924.6″881.8″
1500 yards1087.1″970.6″924.7″
Drop at extended ranges

I’ll be a monkey’s uncle. I’m almost flabbergasted by the implications of this data.

Turns out the 120 grain started out with the flattest trajectory, but that only lasted a little past the 500 yard mark. At its maximum effective range of 1150 yards, the 120 grain load experienced the more drop than the other two loads at the same distance. Remembering that drop is a function of the amount of time a projectile is exposed to gravity or the how long it remains in free fall. This means that the 120 grain with its significantly larger initial muzzle velocity reached the 500 yard marker first, but due to its significantly lower BC it lost so much velocity that it was the last to reach the 1150 yard marker.

While I didn’t include any data under 500 yards in the table, the ballistic calculator shows the drop between the 140 grain and the 147 grain load to be identical all the way out to 350 yard mark. By the 375 yard mark, the 140 grain begins to experience more drop. This means two things. First, the initial muzzle velocity difference of 15 fps is insignificant and negligible. Second, the .031 BC (G1) difference is significant. At least significant enough to matter beyond 350 yards where the 147 grain load retains more velocity.

I don’t even want to look at the drift data now. But, here it is anyway.

Drift120 gr ELD Match140 gr ELD Match147 gr ELD Match
500 yards18.1″14.4″13.4″
1000 yards88″66.8″61.1″
1100 yards100.7″83.3″76″
1150 yards123.2″92.4″84.2″
1200 yards136.6″102.1″93″
1300 yards165.5″123.3″112.1″
1375 yards189″140.8″127.9″
1400 yards197.1″146.9″133.5″
1475 yards222.5″166.1″151″
1500 yards231.2″172.8″157.1″
Drift with a 10 mph cross wind at extended distances

Finally, one of my assumptions was correct. In terms of drift, it turned out that the heavier bullet experienced less drift. However, given that I almost struck out I’m wondering if this was really a result of the bullets weight or the BC. I suspect it’s the latter rather than the former.

Generally speaking, I have found that heavier projectiles of the same caliber and projectile design tend to have a larger BC. Again, I’m starting to wonder how much truth there is in that generalization and will probably start looking for exceptions. Does it hold true for all projectile designs of the same caliber? What about the same projectile design in different calibers? I’m pretty confident I can find examples of heavier projectiles with lower BC if I all projectile designs and caliber restrictions. But at that point, I’m not sure bullet weight matters.

At the beginning of this article I set out to learn what the difference in bullet weight means and whether or not it matters. In the context of the same cartridge with similar projectiles, I can now confidently say that different bullet weights mean different initial muzzle velocities and different ballistic coefficients. In terms of long distance target shooting, the difference in weight definitely matters.

Does this mean that for long distance target shooting the 147 grain load is the king of the loads I compared? On paper, it looks like the answer is yes. However, I really didn’t explore recoil impulse or perceived recoil. Then there is the “different rifles like different loads” canned advice that is commonly found in the community. So, I can’t definitively and confidently say yes, the 147 grain load is king.

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