6mm ARC

[HuntTXhogs]

One can shoot 100gr 6mm bullets at 2700 FPS and one can shoot 100gr 6.5mm bullets at 2700 FPS. I would think the 6mm would be better suited for longer range applications.

I too thought the same about a week ago - figured 6-ARC would just be a means to shoot 1k .243 bullets I have collecting dust at the same velocity as my 6.5 Grendel , I.e. no real advantage inside of 300 yards.

But then I got to shopping for 6-ARC components and that’s when I realized that I had oversighted on some critical aspects of the head to head.

SPECIFIC TO ONLY 90 GRAIN PROJECTILES :

90 grain bullets available for 6mm ARC: 10

Game changer, eld-x, Nosler BT, GMX, Accubond, scirocco, e-tip, Berger target, HotCor, Scenar

90 grain bullets available for 6.5 Grendel: 2

TNT, Varmageddon

90 grain bullets available for 6.8 SPC : 2

Gold Dot, TNT

Advantage 6mm ARC - all three calibers drive them to about the same velocity -

And usually sectional density would be less for 6mm BUT from what I’m seeing in comparing the closest apples to apples is intriguing .

6mm HotCor sectional density : .218

6.5mm TNT : .188

6.8 SPC TNT : .168

Advantage 6mm ARC

I posted the above in another forum and nobody commented - I think this is a possible huge upside waiting to be explored in the hunting fields - I offer it to y’all for comment and thoughts ...

While I wait for a barrel to GO HOT

[HuntTXhogs]

And adding to the mystery: long ago I recall folks saying NOT to use the 90 grain GoldDots for hunting in 6.8 SPC - they were ineffective on medium to heavy game, specifically hogs

Yet we know that the 90 grain TNTs will kill many hogs

So in loose comparison that’s what a potential difference of .20 in sectional density might do...

[Mitdr774]

Weight for weight the smaller diameter should have a higher SD and potential for penetration. I was just over simplifying with my statement. I will probably add a 6mm ARC for the same reason I picked up a 6.5G. The Grendel is a more cost effective 6.5mm alternative to my 6.5x55 and the ARC would be a more cost effective alternative to my .243. The ARC should be easier on the barrel as well. The .243 sure does get hot quick.

[HuntTXhogs]

Weight for weight the smaller diameter should have a higher SD and potential for penetration. I was just over simplifying with my statement. I will probably add a 6mm ARC for the same reason I picked up a 6.5G. The Grendel is a more cost effective 6.5mm alternative to my 6.5x55 and the ARC would be a more cost effective alternative to my .243. The ARC should be easier on the barrel as well. The .243 sure does get hot quick.

The 90 grain is sort of a anomaly in the current market where manufacturers are focusing on producing long and heavy 6.5 and .277 bullets for 6.5 Creedmoor and 270 Winchester .

The limited offerings in 6.5 and 277 that fit within Grendel and 6.8’s grain weight are short and stubby whereas the 6mm 90 grain are longer and therefore have a higher sectional density.

I believe we will come to realize that the 6-ARC will have a very potent punch for an AR-15 frame with the 90’s...

[Harpoon1]

The limited offerings in 6.5 and 277 that fit within Grendel and 6.8’s grain weight are short and stubby whereas the 6mm 90 grain are longer and therefore have a higher sectional density....

Sectional density is a function of weight and diameter, not length or shape. Maybe you meant Ballistic Coefficient?

https://www.chuckhawks.com/sd_beginners.htm

https://www.chuckhawks.com/sd.htm

[Mitdr774]

SD might be a function of weight and diameter, but as you go up in diameter you also loose length for the same given weight. While length may not be part of the math equation to figure out SD, it is something that is involved in the final product. Given the same construction and design, a long "heavy" 6mm will have a better SD than a short "lightweight" 6.5mm if they are both the same weight. This long and heavy for caliber should also result in a better BC.

Nosler Partition 100gr (all numbers sourced from Midway)

.243" SD of .242, 1.065" length, G1 BC .384
.257" SD of .216, 1.035" length, G1 BC .377
.264" SD of .205, 0.962" length, G1 BC .326

[Harpoon1]

SD might be a function of weight and diameter, but as you go up in diameter you also loose length for the same given weight. While length may not be part of the math equation to figure out SD, it is something that is involved in the final product. Given the same construction and design, a long "heavy" 6mm will have a better SD than a short "lightweight" 6.5mm if they are both the same weight. This long and heavy for caliber should also result in a better BC.

Nosler Partition 100gr (all numbers sourced from Midway)

.243" SD of .242, 1.065" length, G1 BC .384
.257" SD of .216, 1.035" length, G1 BC .377
.264" SD of .205, 0.962" length, G1 BC .326

Not sure what your trying to illustrate with those “numbers sourced from Midway”. No one said higher SD bullets can’t be longer, I’m saying length is not the reason why they have a higher SD, that’s all.

How do you reconcile this? Compare two 90 grn 6mm bullets. One solid lead, the other solid copper. I think most would agree the solid copper bullet would then have to be much longer because, copper is less dense than lead. Right? Yet both would still have the exact same SD. And the solid copper bullet, all things being equal, could also have a much higher BC, yet the same SD.

[HuntTXhogs]

I didn’t mean ballistic coefficient - I’m talking about sectional density BUT I will grant that I don’t fully understand the calculations to establish what SD is for a given bullet. Even after reading the Chuck Hawks page I couldn’t get the formula to spit out the SD for a known weight and caliber and the charts are confusing as heck...

Here is what SD means to me :

Note- I’m probably wrong from a technical aspect but given my approximations I’m thinking I’m more right than wrong in realistic application (hunting only).

This article is where I derived that bullet length has an impact on SD : https://ronspomeroutdoors.com/blog/bulle...y-matters/

Again maybe I’m reading it wrong but there are a few statement in the article that clearly lead a lay man to believe bullet length is a contributing factor to SD.

Now, in my head, I rely on some past experiences and posted data (Midway will work for this example) to derive a understanding of what I’m shooting into game.

When I pick up a 223 I ordinarily choose a 62 grain bullet / when I pickup a .243 it shoots a 95 grain / 308 is usually 165 grain / 458 will dispense a 250 grain and so on.

As I look at the available ammunition and bullet choices the number of options are generally clumped in the bullet weights above - these represent the grain weights with the widest hunting utility in the field (no speciality utilization). AND I don’t need to run and grab a calculator but I’d bet a steak dinner that the SD is higher as you work from . 22 to .458....

MY POINT: for the 6-ARC discussion and 90 grain bullets available in other calibers that match the AR-15 profile (Gren and 6.8) is that hunters can only choose what the market bears (ammo makers have focused on other weights for 6.5 and .277) and so in this case the SD charts are thrown upside down because the 6mm 90 grain has a higher SD grain for grain - which isn’t the norm when typically “stepping up” in calibers.

Hopefully this explains my position and understanding a bit more -

Oh and don’t get me wrong, if you give me a 308 and I get to choose the ammo to hunt hogs from 3 grain weights (110 grs / 165 grs / 220 grs) I’m going to choose the 165 grain all day long (given the same bullet construction/properties). That choice isn’t based on SD alone rather there is recoil, trajectory, and penetration all factoring into that decision.

But I’ve learned to never discount a few special grain weights and caliber combos that buck the math and just work and work well despite the ordinary school of thought - the 90 grain Speer TNT on hogs is one of those “Huh?” choices for hogs.

And therefore what if I could supercharge that 90 grain TNT - I.e. 6-ARC bonded bullet (YES theoretically speaking)

[Harpoon1]

I didn’t mean ballistic coefficient - I’m talking about sectional density BUT I will grant that I don’t fully understand the calculations to establish what SD is for a given bullet. Even after reading the Chuck Hawks page I couldn’t get the formula to spit out the SD for a known weight and caliber and the charts are confusing as heck...

Here is what SD means to me :

Note- I’m probably wrong from a technical aspect but given my approximations I’m thinking I’m more right than wrong in realistic application (hunting only).

This article is where I derived that bullet length has an impact on SD : https://ronspomeroutdoors.com/blog/bulle...y-matters/

Again maybe I’m reading it wrong but there are a few statement in the article that clearly lead a lay man to believe bullet length is a contributing factor to SD.

Now, in my head, I rely on some past experiences and posted data (Midway will work for this example) to derive a understanding of what I’m shooting into game.

When I pick up a 223 I ordinarily choose a 62 grain bullet / when I pickup a .243 it shoots a 95 grain / 308 is usually 165 grain / 458 will dispense a 250 grain and so on.

As I look at the available ammunition and bullet choices the number of options are generally clumped in the bullet weights above - these represent the grain weights with the widest hunting utility in the field (no speciality utilization). AND I don’t need to run and grab a calculator but I’d bet a steak dinner that the SD is higher as you work from . 22 to .458....

MY POINT: for the 6-ARC discussion and 90 grain bullets available in other calibers that match the AR-15 profile (Gren and 6.8) is that hunters can only choose what the market bears (ammo makers have focused on other weights for 6.5 and .277) and so in this case the SD charts are thrown upside down because the 6mm 90 grain has a higher SD grain for grain - which isn’t the norm when typically “stepping up” in calibers.

Hopefully this explains my position and understanding a bit more -

Oh and don’t get me wrong, if you give me a 308 and I get to choose the ammo to hunt hogs from 3 grain weights (110 grs / 165 grs / 220 grs) I’m going to choose the 165 grain all day long (given the same bullet construction/properties). That choice isn’t based on SD alone rather there is recoil, trajectory, and penetration all factoring into that decision.

But I’ve learned to never discount a few special grain weights and caliber combos that buck the math and just work and work well despite the ordinary school of thought - the 90 grain Speer TNT on hogs is one of those “Huh?” choices for hogs.

And therefore what if I could supercharge that 90 grain TNT - I.e. 6-ARC bonded bullet (YES theoretically speaking)

I agree with most of everything you say. The devil is in the details.

Spomer says “ Stated simply, the longer your bullets in any caliber, the higher their sectional density and the better their chances for deep penetration, all else (bullet materials, construction and velocity) equal.”

I read that as, within the same caliber, a longer bullet will have a higher SD because, all things being equal and “SAME CALIBER” being the operative phrase, “longer” implies being “heavier”.

Further down in the article, he kind of contradict his earlier “long and heavy” declaration when comparing the Swift A frame and the Scirroco. The Scirrocco is longer, has a higher BC, both have the same SD. Yet the Scirroco with a higher BC and same SD may not penetrate as well because of its construction, I.e. thinner jacket and quicker to mushroom, being cup and core and shedding more lead (mass) vs a-frame, etc...........

My only point was, you can’t assume because a bullet is longer, it will have a higher SD and more penetration. That’s all.

Peace.

[grayfox]

From Harpoon:
"My only point was, you can’t assume because a bullet is longer, it will have a higher SD or have more penetration. That’s all." Technically correct, but practically IMO not very useful to me as a shooter as I will go into below.

The formula for sectional density (SD) is:
SD= M/(D^2), where M is the mass of the bullet (in lbs, or grs/7000); and D is the diameter of the bullet (inches).
SD = [Mass (in grains) / 7000] / (bullet-diameter in inches)².

So technically speaking the "Length" of the bullet is not required. BUT, practically speaking, (and Spomer indicates this as well), for given bullet constructions, more length in a caliber means higher SD due to higher mass.... and as well, smaller diameter for same-style bullets of EQUAL mass will also yield higher SD. It might be true concerning the comment above about all-copper vs all-lead pills at equal mass, but there are no all-lead bullets we shoot, and few all-copper. So that is not a strong distinction, nor do many guys consider that when choosing a caliber or bullet, (this is my guess).

The material variations of copper jacket/composition/thickness for different mfrs, or lead alloy composition; are minor and beyond our ability to control, so the boundary condition of "similar bullet construction" usually applies. So practically speaking, as DNS illustrates, you pick the bullet for the purpose b/c you have already decided on the gun (ie, caliber)...

If we want to compare over different calibers, then constant mass in varying diameters (bullet construction being mostly constant), means smaller diameter will necessarily have a longer body, since the SD comes from the Mass/D^2 figure, SD will increase for the smaller diameter-caliber over the larger caliber, under these bounding conditions. As shooters we typically have a finite list of bullets to choose from, so SD comes from either a longer/heavier bullet at one caliber or a smaller caliber bullet of equal (or sometimes even smaller) mass. It just depends on how the formula results come out for those two bullets.

For the 6Arc I would expect, for similar mass values to a 6.5 bullet, slightly better down-range performance within limits. But for the grendel, you have the ability of using heavier bullets, which usually means better KE for many hunting applications.
In my case, hunting under ~300 yds either caliber will work for my purpose so I plan on having both.

[Mitdr774]

Not sure what your trying to illustrate with those “numbers sourced from Midway”. No one said higher SD bullets can’t be longer, I’m saying length is not the reason why they have a higher SD, that’s all.

How do you reconcile this? Compare two 90 grn 6mm bullets. One solid lead, the other solid copper. I think most would agree the solid copper bullet would then have to be much longer because, copper is less dense than lead. Right? Yet both would still have the exact same SD. And the solid copper bullet, all things being equal, could also have a much higher BC, yet the same SD.

I was stating my source for the information provided. I figured that would be easy to understand, maybe not??

I dont think anyone is arguing that length alters the SD. Reread what I typed, or dont.

Not sure the need to compare different construction when bullets of the same construction was what the provided information was about. Sorry I didnt just bow down to your massive wisdom and accept your gospel without making a factual observation of my own.

[Lemonaid]

A link with lots of links about 6mm ARC https://www.midsouthshooterssupply.com/a..._6arc.aspx

[grayfox]

I've got that one on internet "speed dial" Lol!

[Silverjay]

Picked up a box of 95 grain Berger classic hunters. Quickload predicts 2,743 for CFE223 and 2,720 for Hogdon LVR. Any other powders of interest? 8208, TAC, and 3031 all show velocities in the 26’s. I plan to run ladders tomorrow.

[kmon]

Not sure if this one is on the Midsouth site

[video=youtube;jdiFmouGXWc]https://www.youtube.com/watch?time_continue=2&v=jdiFmouGXWc&feature=emb_logo[/video]

[Lemonaid]

Picked up a box of 95 grain Berger classic hunters. Quickload predicts 2,743 for CFE223 and 2,720 for Hogdon LVR. Any other powders of interest? 8208, TAC, and 3031 all show velocities in the 26’s. I plan to run ladders tomorrow.

H 4895, Varget, Blc(2), AR comp, should be worth a look at some point.

[Old Bob]

Not sure if this one is on the Midsouth site

[video=youtube;jdiFmouGXWc]https://www.youtube.com/watch?time_continue=2&v=jdiFmouGXWc&feature=emb_logo[/video]

In this discussion they didn't cover the reasons why some barrel makers use different than standard gas port locations. I've looked at all of the barrel manufactures Hornady listed as partners in the introduction of the 6mm ARC. Some of them do use standard gas ports but some use locations closer the barrel's muzzle. None of them explained why they put those gas ports where they are. If the 6mm ARC gas system functions efficiently with standard gas ports, why do some makers use the +1 or +2 locations? What is the diameter of the gas port?

[Silverjay]

Data from 95 grain Berger classic hunter and CFE223. Work up slow if you base off of this.

28.0 2,624
29.0 2,688
29.4 2,722
29.6 2,773
29.8 2,795
30.0 2,808
30.2 2,811
30.4 2,838
30.6 2,886
30.8 2,881
31.0 2,917 Quickload predicts pressure at 52,500
31.2 2,901
31.4 2,929

Ejection pattern shifted from 4:00 to 3:00 at 31.0 grains and higher. The case and volume data I used for 108 ELD’s gave almost exact velocities, same cartridge data for this load predicted 2,720 at 31.0 grains and actual was 200 FPS faster. No pressure signs on the brass. Primers are S&B ST and still have nice rounded shoulders. No ejector marks.

Across a 10 round set of 31.0 grains the average velocity was 2895 with an SD of 6. This is at 93 degrees F ambient.

[A5BLASTER]

Data from 95 grain Berger classic hunter and CFE223. Work up slow if you base off of this.

28.0 2,624
29.0 2,688
29.4 2,722
29.6 2,773
29.8 2,795
30.0 2,808
30.2 2,811
30.4 2,838
30.6 2,886
30.8 2,881
31.0 2,917 Quickload predicts pressure at 52,500
31.2 2,901
31.4 2,929

Ejection pattern shifted from 4:00 to 3:00 at 31.0 grains and higher. The case and volume data I used for 108 ELD’s gave almost exact velocities, same cartridge data for this load predicted 2,720 at 31.0 grains and actual was 200 FPS faster. No pressure signs on the brass. Primers are S&B ST and still have nice rounded shoulders. No ejector marks.

Across a 10 round set of 31.0 grains the average velocity was 2895 with an SD of 6. This is at 93 degrees F ambient.

What length barrel?

[Silverjay]

20”