6mm ARC

[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.