I don't understand

[Red Delicious]

I'm in need of education and knowledge, hope you can help me out.

I read threads on the 6.5X284 sending 140 gr bullets at 2900 to 3100 fps being fine for bull Elk at 800+ yds. Yet I read threads on the 7mm Remington Magnum (my round of choice) and a 140 gr bullet leaving the barrel at the same speeds gets laughed at for Elk. Seems you need at least 160 or 180 gr and even then don't shoot beyond 300 yds or so.

What is so magical about that 0.5 mm diameter difference?

Thanks

Craig O.

 

[FAIRCHASE]

Next to nothing. Just differences in opinions.

 

[Wingnut]

It is all about BC and sectional density. The higher the BC and Sectional Density the more energy is delivered down range and the farther it penetrates. The 7 mm 140 has a very low BC which means it will slow down faster down range and deliver less energy and have more wind drift. So for extended range shooting on animals the 6.5 140 grain bullet wins that battle.

 

[bigngreen]

If you take 140 to 140 grain at the same velocities the 6.5 will dominate due to sectional density and BC, then you go out and shoot an elk with each and you'll get visual confirmation!!

 

[wbm]

Next to nothing. Just differences in opinions.

+1.

The 6.5x284 is much more efficient since it burns less powder. The 7mm Mag is my favorite all-round cartridge also. Personally, I would go with the 168gr Berger Hunting VLD for elk at long ranges.

 

[Mtngoat690]

Interesting question. I'll bet it has to do with the same reason(s) why regular old soft points will no longer kill elk? You see from what I understand (based off of the forums and gun magazines I've read) some 10 or 15 years ago elk evolved and became "bullet proof"! Yep you heard it right and along with this they also became so wary and educated that we now must spend thousands of dollars on custom rifles that can shoot baseball size groups at 800 and even 1000yds because we can no longer get any closer to them. To get back on subject......I have a 6.5 and 7mm's that I have shot several elk with and to be completely honest with you, I didn't notice any difference in "on game performance" and I know for a fact the elk couldn't tell a difference.

 

[Red Delicious]

Thanks guys that input helps a lot. I think I 'll try the 150 gr Accubond LR that will give me a higher BC and more SD then the 140 gr 6.5 with at least the same MV. So if they shoot well for me I should be good to go.

Craig O.

 

[bigngreen]

Thanks guys that input helps a lot. I think I 'll try the 150 gr Accubond LR that will give me a higher BC and more SD then the 140 gr 6.5 with at least the same MV. So if they shoot well for me I should be good to go.

Craig O.

Unfortunately the 150 ALR won't get you to either SD or BC of a quality 140gr 6.5 bullet, that is why you see guys going 160+ grain to start pulling better performance out of their 7mm's.
Take a 140 Berger in the 6.5 and your looking at a SD of .287 and a G7 BC of .313, the 150 ALR has a SD of .266 and a G7 BC of .295, much closer but not really equal.
I have yet to catch a 140 Berger in a game animal, mule deer or elk but I've caught many 7mm bullets under 160 grain and had many not get the penetration needed while delivering a good wound channel. There is a reason the 6.5's have been popular for big game for so long.
I prefer to shoot the best bullets I can both for terminal performance and ballistics on elk so we run 150-160 grain Matrix VLD's in our 6.5s and 180 and soon 195 Bergers from our 7mm's.

 

[Red Sparky]

There are three things about bullets. 1) Internal ballistics-The time the bullet is in the barrel. 2) Exterior ballistics-The time the bullet is in the air 3) Terminal ballistics-The damage done to the object the bullet hits.

Now as far as exterior ballistics (2) the 6.5 is better than the 7MM. Look at the bullet drops with the same bullet weight and MV and you will see the 6.5 reaches with higher velocity and less drop. The difference is sectional density (SD) and ballistic coefficients (BC).

Now as far as terminal ballistics go (3) if the bullet has sufficient energy to expand and penetrate they should be equal. The amount of damage to vital organs is what you look at. If both bullets expand and penetrate they should do their job. Bullet composition and jackets, etc. have more to do with terminal ballistics. Examples are Nosler Patitions, and the like, vs. plain Spitzer lead tipped jacketed bullets.

I will use the .44 240 grain Hornady XTP which list the optimum velocity between (I think) 1100-1800fps to have the best terminal velocity as an example. If the bullet hits a deer out of a .44 carbine rifle at 1700fps or out of a ML with 1200fps the bullets should both perform the way they were designed and have maximum terminal ballistics. The animal will not know the difference.

The external ballistics (2) don't really matter as it is the same bullet with the same sectional density (SD) and ballistic coefficient (BC) which apply to exterior ballistics. It is going to fly like a pig with wings. The bullet composition is the same so they will expand and penetrate for the optimum terminal performance.

Where most people make the mistake is applying exterior ballistics (2) to terminal ballistics (3). Comparing apples to oranges as there are complete differences between the two. An example is a boat tail bullet, which has nothing to do with terminal ballistics but everything to do with external ballistics. The Partition and A-frame have nothing to do with external ballistics but a lot with terminal ballistics.

 

[bigngreen]

External and terminal ballistics do have a tie when you start putting on range where BC keeps your bullet functioning better because your retaining velocity. If we shot the same weight bullets at the same velocity but one is loaded with a sleek design hunting bullet and one with a flat base lead nose and you try to utilize them at the same range you'll have very different outcomes. External ballistics or impact velocity, ties very directly to terminal ballistics or bullet function!

 

[Red Sparky]

I don't disagree with you completely. The problem is bullet makers have to build their bullets for many different impact velocities. The reason I gave the XTP example. Your .257 bullet can hit faster (1700fps) but the .284 bullet can hit slower (1200fps). If they are in the proper velocity to expand and penetrate for the bullets they are shooting it makes no difference. The make up of the bullet has more to do with terminal velocity than any exterior ballistics calculation.

As I said you can have the highest BC with the best SD with a long tapered pointed boat tail in .257,.277,.284,.308 or any caliber you want. The hypothetical problem is it is a hollow point with an un-bonded lead core and very thin jacket, so it hits and blows up. No penetration, no wound channel, nothing. All the external ballistics looked good however. Or you can make an all copper bullet that doesn't expand. It has the highest SD and BC with a boat tail, all external ballistics look good but the bullet works just like a FMJ.

So if you build your bullet for terminal performance, bonded lead core or expanding all copper, you control the expansion of the jacket taper for impact velocities, and you keep it together for penetration it does not matter what the external ballistics say. Now you can not have a flying brick so bullet manufacturers have the spitzer or semi-spitzer point and some have boat tails to help with BC and SD.

If external ballistics play so much on terminal ballistics then why did that have to make the Game King and "recommend" the Match King bullets not be used on Game? Do you remember when Match King bullets first came out and blew up on game from misinformed hunters not knowing the difference?

Apples and oranges.

 

[Red Delicious]

Unfortunately the 150 ALR won't get you to either SD or BC of a quality 140gr 6.5 bullet, that is why you see guys going 160+ grain to start pulling better performance out of their 7mm's.
Take a 140 Berger in the 6.5 and your looking at a SD of .287 and a G7 BC of .313, the 150 ALR has a SD of .266 and a G7 BC of .295, much closer but not really equal.
I have yet to catch a 140 Berger in a game animal, mule deer or elk but I've caught many 7mm bullets under 160 grain and had many not get the penetration needed while delivering a good wound channel. There is a reason the 6.5's have been popular for big game for so long.
I prefer to shoot the best bullets I can both for terminal performance and ballistics on elk so we run 150-160 grain Matrix VLD's in our 6.5s and 180 and soon 195 Bergers from our 7mm's.

Okay here's what I've done to try and make sense of this.

I took two bullets.

Make wt BC SD
Berger 140 0.612 0.287 Match grade VLD Hunting 6.5
Nosler 150 0.611 0.266 Accubond LR 7mm

I then put them into my Chrony Ballistics III software each with a muzzle velocity of 3,000 fps, Altitude of 1,000ft Barometric Pressure of 28.47, temperature of 55F, and 78% humidity and zeroed at 100yds. Then I charted it out to 1,000 yds. Here are my results.

bullet ---- distance ----- Velocity ----- Energy ----- path
6.5 ------- 200 ---------- 2702 -------- 2269 ------- -2.3
7 --------- 200 ---------- 2701 -------- 2430 ------- -2.3

6.5 ------- 400 ---------- 2422 -------- 1824 ------- -21.7
7 --------- 400 ---------- 2422 -------- 1953 ------- -21.7

6.5 ------- 600 ---------- 2160 -------- 1451 ------- -65.0
7 --------- 600 ---------- 2159 -------- 1552 ------- -65.1

6.5 ------ 800 ---------- 1914 --------- 1139 ------ -137.7
7 -------- 800 ---------- 1913 --------- 1218 ------ -137.8

6.5 ----- 1000 --------- 1688 ---------- 886 ------ -250.0
7 ------- 1000 --------- 1687 ---------- 947 ------ -250.3


I realize killing potential is more difficult then just velocity and energy but they along with bullet design and most importantly shot placement have to be major players in the equation. So I think I'm coming down on the side of "Fairchase" and "WBM". I've found a gun I'm comfortable shooting now I need to find a bullet designed for the job and will shoot well from my gun. Then get good at shooting it.

Thanks for the help.

Craig O.

 

[bigngreen]

Thanks for the help.

Craig O.

All I'm doing is trying to give you a hand, so if you look at your BC numbers and re run them with the ALR at a G1 BC of .576 which is what they actually are but not advertised at, also it looks like your using a station pressure and the elevation combined, this is like doubling down on the elevation data, could be that your just using a very, very low corrected baro in which case you'd be right.
If you re run the numbers you'll see what I'm talking about.

 

[Red Delicious]

All I'm doing is trying to give you a hand, so if you look at your BC numbers and re run them with the ALR at a G1 BC of .576 which is what they actually are but not advertised at, also it looks like your using a station pressure and the elevation combined, this is like doubling down on the elevation data, could be that your just using a very, very low corrected baro in which case you'd be right.
If you re run the numbers you'll see what I'm talking about.

I really do appreciate the help. I'm not trying to start an argument just understand, hope it comes across that way.

Where do we find the real BC's rather then what the manufacturer advertises? Is there an independent testing facility we can get those numbers from? As I work up loads I'll like to be using the correct data.

Thanks again.

Craig O.