I need a new rifle wanna help.. part 2 sorta..

[*WyoWhisper*]

Yup, Chris is pretty much on the money with my way of thinking...

I realize there is less dope applied to the 6.5's and less elevation applied in the 6.5's

On computers and paper the 6.5's retain more energy down range because of the high B.C.
That all makes alot of sense and will shoot well for a person. But If you do your part and know the rifle, you should know your limits and your effective and accurate range with that rifle...

If you can acheive 2700 fps with the 175's you have 233" of drop and 830 Ft. Lbs. of energy at 800 yards...

Now here's another way to look at it...

a 9mm shoots a fast light bullet....

a 45 shoots a heavy slow bullet

which one will knock down the bad guy quicker with one shot to the chest?

It has always been my philosophy that you don't have to be the fastest or biggest bullet just the most accurate bullet.
Albeit accuracy has many variables.. it is up to you to accurately,quickly and efficiently apply your knowledge to your weapon. To make it accurate...

when it comes down to it if your cartridges are accurate and your rifle is accurate ...

it is all on you....

no brainer and no problem...

just practice...

 

[308175]

Gents,

Not all BC's are what they seem. Because the 308 win is for lack of a better term "ballanced" or as I like to think of it "mathematically square" many bullets fired from a 308 win have much higher BC's than what the books show. I have seen 178 Amax bullets fired around 2550 FPS and had a BC of around .560 I also have found 155 Palma bullets to be closer to .500 at 2900 FPS (in 308)than the .450 Sierra states. Also Sierra will tell you that the 155 palma (in 308) will have a higher BC than the 168 and you can drive em faster, yet their manual states the 168 to be .462 for the 168. Its all interesting stuff, but "real world" The 308 does better than many folks realize.

 

[Brent]

308175,

Surely you're not saying that the cartridge case from which the powder ignites has any more influence on the bullets BC, other than the MV it produces?

How did you determine the 178 A-Max's BC to be around .56? Were you accounting for temp and BP, and is this BC adjusted to standard conditions at sea level?

What conditions did you determine this in? Temp, altitude, and BP?

I like the bigger calibers better, 30 on up are my fav's. In my experience more frontal area does make a difference.

 

[308175]

Brent,

I maybe saying that powder charge in general may have a little to do with BC but not that much. What I am saying is that Because the 308 win is so well ballanced all the way around it becomes much more efficient than a 30-06 or 300 win and so forth. I believe that there is more to BC's than just bullet form and velocity, although these are 2 of the biggest factors. Twist, barrel legnth, twist quality, bore quality, cartride size, demenssions, load density, and of course the ampmosphere and more.

The apmosheric conditions all my testing done was anywhere from 80-100 degrees. BP was anywhere from 28.53-28.74 humidity was anywhere from 30-70% and altittude is 1100' A true MV of 2554 was used and loads are kept about the same temprature for day to day concistency. Unless I am missing something, this is all the input value for the ballistic calculator. Rounds are fired at 100-800 yards, then the clicks are calculated into inches of drop. All data is then put into the calculator with a BC of .500 to start. The BC is increased untill the numbers match. I came up with .560 for the 178 out of my personal rifle. It will not be the same rifle to rifle.

 

[Brent]

After taking a look at the BC numbers using standard conditions at 1100 ft (28.35 BP, 55.1 deg F, 78% HUM), verses the standard sea level condition BC of .495, it jumps to a .5115 BC.

If you increase the BP to 28.53, it drops to a .5082 BC. But, when you raise the temp to just 80 deg F it jumps to a .5363 BC.

Raising the BP to 28.74 at 80 deg F = .5324 BC.

28.74 BP and raising temp to 100 deg F = .5576 BC.

Keeping temp at 100 deg F and lowering BP to 28.53 = .5615 BC

So, using standard sea level conditions (29.53 BP, 59 deg, 78% HUM) in a ballistics program, these corrected BC's (.532 - .562 BC) would be accurate, or the published .495 BC at your atmospheric conditions, same result.

Without knowing the exact temp and BP at the time of the test, and measuring actual drop on the target to 600 yards or so, it leaves too many variables that can poentially skew the BC.

I use an 8' sheet of plywood standing upright covered with freezer paper, using the top edge as a vertical hold point, then fire groups at each 100 yard increment to 600 yards recording "actual" drop in inches with no turret adjustments during the test. The rifle is zeroed "perfectly" at 100 yards before the test, or at least verified before hand. MV, temp and BP are recorded with the Kestrel 4000 at this time before each test.

I believe this is probably the single most effective, and accurate method to determine a bullets BC, but I also use the Oehler M43 with screens at the muzzle, and downrange screens hooked to the Oehler 35P for a two range MV determination of BC, or simply use the acoustic target and the M43.

Of the three ways of doing it though, I still prefer the plywood while measuring drop in inches over anything else. All have given me reliable numbers "if" all conditions are known exactly.

After BC and drops are known, shooting at these ranges again while "dialing" the zeros in will confirm your turrets accuracy, or point out a thread inconsistancy, uncalibrated pitch, etc, etc.

Twist rate will affect stability, and this will affect the BC, the other effects are probably unmeasurable, or unprovable, as the effects would be so small IMO. MV, temp and BP are major factors at LR, as is the recoil effect from various rests or shooting positions.

The 308 is an efficient round, as is the 300 WSM, although I believe bullet inconsistancies and imbalances contribute to BC variations. Twist consistancy, bore and groove quality, and diameter, powder selection for a specific cartridge, load density, bullet base shape, jacket thickness, core hardness, muzzle pressure, barrel length and diameter are factors that contribute to bullet stability, balance, and integrity, and thus it's BC, all aside from the bullet itselfs consistancy.

 

[Michael Eichele]

Hey Brent,

While I cannot vouch (yet) for such a high BC in 178 AMAX, I can vouch for the 155 Palma fired from a 26" 308 in the opposite envioronment. The tests I did w/the palma bullet were at zero degrees to -10 F. The BP I used was from a pilot friend of mine and was the standard. Altittude was 600' (which is irrelevant due to BP input) Any way, I zeroed the rifle at exactly 600 yards. The 20 MOA hold over I used drilled groups perfect at 1000 yards. The calculator stated (using .450) that drop would be 250" at 1000 yards. 20 MOA = approximately 210" at 1000 yards. This is a 40" differance. A BC of .500-505 inputted into the calculator solved the "mystery" of why these loads shot so high. This test was performed repeatedly with the same results.

I am going to do some tests w/the AMAX, while I have done a little, I havent done much. I do know that The last couple of times I shot the 178 AMAX, I was using the wrong muzzle velocity and a BC of .525 The MV I was using was 2610. I have discovered in the last few days, I was mistaken. My MV is 2566. I had not chronied my loads and just fired them at extended ranges. Because most shooters agree that the BC of the 178 is .525 thats what I used. I then calculated using all conditions except for BP. I came up with 2610. They are in fact (now that I chronied them) 2566. Now either the BP was way off those 2 saturdays in a row, or the BC is higher out my 308 than I thought. Brent, scince you live by where I shoot, would you happen to know the BP on 12-6 and 11-29??

PS I also know that the 1 time I fired the AMAX at 1k they were way high, like 2.5 feet, somewhere in there. I was using an 800 yard zero and they shot that high. BP maybe?? BC, maybe. This weekend might tell the tale if I can get you to email me a BP reading saturday, or you can meet me out there same place same time.

L8r

[ 12-19-2003: Message edited by: meichele ]

 

[Michael Eichele]

I also just rememberd that the BC I had come up with for the 175 SMK was .500 and that worked just fine out to 600 yards, and if I remember 1000 as well. I cant imagine those 2 bullets being that much different. Although the longest 175 SMK I have seen was 1.250" the last batch of 178s I got are 1.330" long. The 190's I had used were at .551 as apposed tho the .534 the Sierra reloading manual reads.

[ 12-19-2003: Message edited by: meichele ]

 

[Michael Eichele]

It has been determined that the 178 has a BC of .525 out to 700 yards from my rifle.