: Long range hunters, opinions on B.C.

15 May 2003, 10:27

I remember reading a post stating that ballistic coefficient in a hunting situation really can't be counted on. Too many "environmental" variables.

I thought that a higher BC also meant that the energy is carried further, which for those who shoot at 500, 700 or 1000yards would be very important.

Although this question is geared toward a big game scenario, my curiosity is trying to talk me into getting a 22PPC to replace my 6PPC, with the thought that a .22cal 50grain bullet will have a higher BC and therefore shoot better.

Seeing as I don't have much use for 70gn bullets, using 50gn ballistic tips for roe and fallow does, I thought I may as well rebarrel to 22PPC...

I doubt I could tell the difference, but it would be nice to know. [Razz]

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P.S. I checked this out and found that with some bullets, it can be found that a .22cal bullet will have a higher BC than a .243cal of the same weight, but the difference is negligable.

[ 05-15-2003, 02:30: Message edited by: EXPRESS ]

15 May 2003, 13:19

DigitalDan

Just my opinion but I think they're both kind of bum choices for anything larger than varmints. The BC's of the bullet weights and calibers you mention are poor and the Ballistic Tips are extremly frangible.

Having said that, I realize that Roe deer are not large and perhaps you can pick and choose your shot. It is not clear what range ou expect to shoot at but in general terms any spitzer bullet is a fair bet for retained velocity etc. at 300 yards or less, so the BC question does not take on significance until proceeding beyond that range. 6mm PPC twist rates will not stabilize bullets suitable for long range work in that caliber, and I doubt the 22 PPC will either. If you are contemplating shots beyond 300 yards with those calibers get something with more powder capacity and a faster twist to accomodate 60 gr or heavier .22's or 100+ gr 6mm bullets.

15 May 2003, 20:47

Brent Moffitt

It's all centered around the bullets time of flight... period.

A bullet that gets there quicker will have less time to drop (be affected by Gravity) or move from wind... period.

Trajectory is determined by MV and BC, enviromental conditions affect the time of flight too but can be accounted for easily. Temperature is the worst enemy, it affects MV if your powder choice happens to be temp sensitive and it also means air density change (more or less drag).

For comparison sake, the bullet with the higher speed and same BC will shoot flatter and drift less from wind. The same is true for a bullet thats velocity is the same but has a higher BC.

Energy at the target is dependant on time of flight too. The less time it takes a bullet to get to the target, the more energy it retains because it retains more velocity at the target.

Get a fast twist barrel suitable for long range bullets, you know the speed they must go to accomplish the trajectory goal, so select a case that will get you there. Caliber is your choice.

My dads 6.5wsm is shooting 140gr SMK's at 3250 fps in a 30" bbl. It's practically a laser! [Smile]

18 May 2003, 13:02

Jon A

quote:
Originally posted by Brent Moffitt:
A bullet that gets there quicker will have less time to drop (be affected by Gravity) or move from wind... period.

Actually, that's not quite right Brent. A bullet's BC has a much larger effect on wind drift than it does on drop.

A lighter, lower BC bullet will drop less and have a smaller TOF than a heavier, higher BC bullet that is launched more slowly (within reason) but the light, low BC bullet will almost always have more wind drift--even if it shoots flatter and gets there more quickly.

That's why high BC's are so important to LR accuracy--you can always compensate for drop but compensating for the wind is more difficult.

18 May 2003, 19:43

Petander

Well put,folks. Combined all the above is my reason to use 300gr SMK in .338 Lapua.

The wind is the hardest part to deal with,considering accuracy. Of course the energy stays better as well with a high BC /SD but that comes as a bonus. [Big Grin]

Hmm...those boolits are still in MI but a friend will ship them ASAP.He accidentally swallowed one of them,I kindly asked him NOT to include it in the box... 499 boolits will take me a long way,probably ï¿½till July [Eek!]

[ 05-18-2003, 10:46: Message edited by: Petander ]

19 May 2003, 04:31

DigitalDan

July? You shoot a lot paleface. [Big Grin]

I think the best way to understand the way BC affects drop and 'drift' is to look at it from the perspective of drag vectors. Drop is a gravity issue and has nothing to do with form but rather TOF(yeah, I know about lift but it is an inconsequential issue). Of course a lower BC will cause longer TOF and more drop but that is all. The effect of wind is that of a deflection on a gyroscopically stabilized projectile. TOF is a predominate consideration that is tempered by DRAG, so when one says this is more than that etc., it must be qualified by just how far you're shooting and what the delay time is. Bullets do not drift at wind velocity value and actually resist that significantly(do the math, it's simple). It is true that a .17 Rem or .220 Swift will have less 'drift' than perhaps a higher BC but lower velocity bullet but only at shorter ranges. When the distance of the shot grows to lots of 100's of yards or more the hot rock hi-vel freaks are sucking wind if they don't back it up with high BC's. The delay or loss of velocity(drag vector) is the significant factor.

19 May 2003, 06:04

<allen day>

High BC is important for long-range hunting applications, but don't become so fixated on BC for its own sake that you ignore everything else. For hunting purposes, bullet construction (up to a point) is more important than high BC, and it can be a very bitter bargain indeed to choose a poorly constructed bullet just because it has a high BC. I've done it, and it's a misdirected approach.

The vast majority of big game is taken at less than 300 yards (most under 250 yards), and there are a whole slew of bullets available with an acceptably high BC to get the job done at any normal hunting range.

You can have a high BC with reliable construction in one package. For example, you can choose the 180 gr. Nosler Partition Spitzer (BC .474) instead of the 180 gr. Nosler Partition Protected Point (BC .361). If you load these bullets to 3100 fps. in the .300 Winchester and zero for 250 yards, the difference in drop is only -0.4" at 300 yards. But at the 400 yard mark the superior BC of the Partition Spitzer makes itself known. At this range the difference in trajectory is -15.0" for the Protected Point versus -9.7" for the Spitzer. So you've given yourself a 5.3" trajectory advantage at 400 yards just by choosing a bullet of superior BC, yet of identical construction, and that 5+" can mean the difference between a hit and a miss at long range.

AD

[ 05-18-2003, 21:10: Message edited by: allen day ]

19 May 2003, 08:38

Jon A

I agree that BC's are not very important under 300 yds, but the question was at long range. When using a rangefinder, I wouldn't be as worried about the extra drop at 400 as the extra wind drift in Allen's example. I'd just click the scope about 5 more times. [Big Grin]

But reading the wind is as much of an art as it is a science. I need all the advantages I can get.

Let's try another example to illustrate what I said above--the 180 PP at 3100 vs a 200 AccuBond at 2900.

At 400 yds they both have almost identical TOF and drop. But the PP point has 5.5" more drift in a 10 mph wind. At 500 yds the AccuBond will shoot flatter as well. So let's bump the PP up to 3300 FPS so it actually has a lower TOF and will drop less at 500 yds. It will still have 7.2" more wind drift even though it's faster and flatter at that range.

The point being at this range the extra velocity makes up for the blunt shape of the bullet and gives you a better trajectory. But it's still at a large disadvantage in wind drift.

The real-world application of that is this: If you want to kill something at 500 yds (whether or not one should is a debate well covered in the MK thread so let's keep it out of here) you'd be better served with a WSM shooting a high BC bullet than a RUM shooting a low BC bullet. You'll be better able to precisely place your shot even if the wind is only a light breeze. Your scope will have plenty of clicks left at that range. [Wink]

Oh, and while the PP starts out with 600 ft-lbs more energy, it has about 400 ft-lbs less at that range.

19 May 2003, 08:39

Brent Moffitt

Jon,
I stand corrected, I'm following you. [Smile]

An example so we're on the same page here.

6.5wsm (30" bbl)
Temp = 59 deg F
BP = 29.53

123gr Lapua Scenar

BC = .574
MV = 3500 fps

69gr RL25
OAL = 3.08"

140gr Berger

BC = .630
MV = 3225 fps

67gr RL25
OAL = 3.1"

At 1000 yards, I come up with;
53.23in drift on the 123gr, and 51.35" with the 140gr.

215.21" drop on the 123gr, and 244.36 with the 140gr.

TOF is 1.159 seconds for the 123gr and 1.221 for the 140.

Good point. I'm sure there are more dramatic comparisons though, the 123gr bullet has quite a high BC and is cookin too, it does illistrate the point though. [Smile]

Jon, you posted right before me... good example there. [Wink]

[ 05-18-2003, 23:44: Message edited by: Brent Moffitt ]