Efficient Cartridges

[Stinky Coyote]

Agree if you reload the 7-08 is the 20th century version of the 21st century 6.5 Creedmoor when you fire up some 7mm 162's and I think Tikka's and maybe more have a twist that can support it without a rebarrel? You won't find factory ammo in the 7-08 that can run with factory 6.5CM though so I personally deduct a few points on the 7-08 due to not 'fully off the shelf', also those 162's will push the shoulder potentially out of the comfort window for hitting more shooters abilities.

Either way though, both are top choices that cover a bulk of the parameters you can choose from. Very balanced, very efficient. 6.5 CM wins fractionally on a couple points imo but splitting hairs on the two.

 

[Forestryguy]

Not sure it will work out as you're thinking as you may eek out a bit more ft/lbs from something shooting a bigger fatter slug but that slug may fall on it's face 150 yards out the end of the barrel? So one has to make their list of parameters important to them before starting to find what's most efficient to them and it's a dynamic list available. Some of the options could be...

Max Distance Potential
Max Size Game
Minimum Sectional Density
Minimum Impact Velocity
Minimum Impact Energy
Minimum Bullet Diameter
Minimum Bullet Weight
Recoil Energy
Barrel Life
Time of Flight
Wind Drift
Factory Availability
MPBR (max point blank range)
Accuracy

I don't choose all of the above parameters and have maybe missed listing some but I do choose a good many of them. I always start with the bullets, then apply the range potential I want, then I can figure out the head stamp that will drive said bullet out to max distance and minimum fps impact thresholds without any extra fat.

The easier button to find the most versatile from that list above currently would to just look at the 21st century 6.5's with bullets in the 123-156 range as they run the highest SD's & BC's and extract the most from the powder burned in terms of terminal performance/distances, game it can take, recoil, barrel life, wind drift, time of flight, factory availability etc. They just do more of the above for the powder burned than the 20th century cartridges and very early 21st century (wsm) etc. Examples below...

The 6.5 Grendel with a 123 will give you the most from ~30 grains of powder, the 6.5 Creedmoor will give you the most of ~41 grains of powder and and 6.5 PRC ~59 grains. Each option giving you approx. ~200 yards further potential with both the CM & PRC giving higher SD & heavier bullets that fight wind better also but better for more 3rd class game.

6.5G 123gr at 95% factory rated velocity - 1800 fps lands at 450 yards, recoil energy in 8.5 lb rifle at 6.8 ft/lbs. SD .252, BC .506, barrel life is that of a .22lr

6.5CM 143 as above at 1800 fps lands at 650 yards, recoil 11.3 ft/lbs, SD .293, BC .625, barrel life - longer than anything but the Grendel.

6.5PRC 143 as above at 1800 fps lands at 825 yards, recoil at 17.9 ft/lbs, SD .293, BC .625, barrel life - as good as anything that will kill big game at 850 yards.

Niche ends; the PRC makes you eat a more manly 17.9 ft/lbs recoil energy so give up on the shootability for the smaller shooters and some barrel life. The Grendel gives up some SD/BC so just gets into the 3rd glass game bullet size and more suited to bulk of game being 2nd class but it's wins are unlimited barrel life and shootability for anyone with single digit ft/lbs recoil energy. It still does well inside 500 yards which will work for most.

The 6.5 CM however has no weak areas, it captures the majority of the categories the most equally, I can't think of anything that will touch it for near 41 grains of powder burned.

Anyway, hope that's a contribution to the topic. It's a dynamic one.

Its about midnight and I have ben studying all day, so I may be reading this wrong? Wondering how you are coming up with 825 for PRC vs 650 for CM if both are 143s, 1800 fps? And PRC has a higher charge? Differences in powders, barrel lengths?

 

[Forestryguy]

Came across the Vortex Cast about the 6.5 BC they are working on.

Anyone know more about this case, or the way it was machined? Kind of wondering if this would make a standard cartridge more "efficient" in powder to MV? A thicker case wall would increase pressure so less powder would be necessary to reach same MV? Then use a modern high BC projectile, seated further out, to increase range. Or, modify case so that bullet is seated to ogive, but not deep in powder column.

 

[Dos Perros]

Efficiency, to me, (if that's what we're doing here), should be evaluated as:

grains of powder burned / pound of meat in the freezer

By this measure, one would select for cartridges that are accurate AND have some minimum downrange energy. And obviously good choices in bullets to make good use of that energy.

My opinion: just go hunt dude!

 

[Harvey_NW]

This is interesting, and I think it can easily be overthought or debated based on personal expectations or interpretations of "efficiency". But in a sense of the word, I've steered my attention toward the concept. In the .284 category I was burning 69gr of H1000 and getting avg 3,020fps with a 168gr VLD, I ditched the belted mag and now have a 280ai that is burning 58.4gr of powder and launching the 162 eld-m at avg 2,800fps, that's a pretty mild load and the rifle only has 86 rounds down the tube so it hasn't sped up.

I also have a 6 creed, and am having a 25 creed barrel spun into a Tikka action at the moment, I think in terms of efficiency and ballistics the creed based cartridges are really hard to beat.

But there will always be a pretty direct relationship between powder, pressure, speed, and recoil. When you really dice it out it's usually close enough that it's not worth going with one because you save a few grains of powder to get the same velocity, things like brass quality/availability will usually outweigh that idea.

 

[z987k]

This is interesting, and I think it can easily be overthought or debated based on personal expectations or interpretations of "efficiency". But in a sense of the word, I've steered my attention toward the concept. In the .284 category I was burning 69gr of H1000 and getting avg 3,020fps with a 168gr VLD, I ditched the belted mag and now have a 280ai that is burning 58.4gr of powder and launching the 162 eld-m at avg 2,800fps, that's a pretty mild load and the rifle only has 86 rounds down the tube so it hasn't sped up.

I also have a 6 creed, and am having a 25 creed barrel spun into a Tikka action at the moment, I think in terms of efficiency and ballistics the creed based cartridges are really hard to beat.

But there will always be a pretty direct relationship between powder, pressure, speed, and recoil. When you really dice it out it's usually close enough that it's not worth going with one because you save a few grains of powder to get the same velocity, things like brass quality/availability will usually outweigh that idea.

The thing I like about less powder a lot of people forget, is that in the recoil equation, it's not just the bullet weight that is accelerated, it's the mass of the powder as well. Which translates to less equal and opposite.
If I can get very close to the same performance - 280AI vs 7RM is a good example, with a lot less powder, that means less recoil, which in reality means more accuracy.

 

[Forestryguy]

Efficiency, to me, (if that's what we're doing here), should be evaluated as:

grains of powder burned / pound of meat in the freezer

By this measure, one would select for cartridges that are accurate AND have some minimum downrange energy. And obviously good choices in bullets to make good use of that energy.

My opinion: just go hunt dude!

I agree that just going hunting is the best spent powder. But, there is no hunting season open right now, I am in an intensive Nursing program and have no time to shoot, but my head still wonders about hunting and shooting. Plus, I like tinkering with things to make them better.

If no one ever tinkered, wondered we would still be living in a cave with no fire.

 

[Downeaster]

The easy answer is as many have already said... .308 based cartridges (most anyhow). If you wanted to be REAL efficient id say my 6mmBR shooting a 105 Berger at 3000fps w 30gr of varget is hard to beat.

That being said, the big boomers really are all that trips my trigger these days. The heart wants what the heart wants...as a wise man once said

 

[Stinky Coyote]

Its about midnight and I have ben studying all day, so I may be reading this wrong? Wondering how you are coming up with 825 for PRC vs 650 for CM if both are 143s, 1800 fps? And PRC has a higher charge? Differences in powders, barrel lengths?

the 6.5 prc launches around 2950 fps and the 6.5 cm launches about 2700 fps, a lot of people use 1800 fps impact velocity as minimum threshold for bullet performance on game, launch the same bullet faster and this 1800 fps distance grows further

if you launch at 2950 fps it takes until 850 yards for that bullet to slow down to it's 1800 fps minimum impact threshold, the creed launching at only 2700 fps means about 600 yards is your max...one of them is burning about 40% more powder than the other, translates to distance potential