• The Shot You’ll Never Forget Giveaway - Enter To Win A Barrel From Rifle Barrel Blanks!

    Tell us about the best or most memorable shot you’ve ever taken. Contest ends June 13th and remember: subscribe for a better chance of winning!

    Join contest Subscribe

ARE THESE 7MM BC's CORRECT AND TRUE???????????????

#2
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

I'm going to do some load devlopment and testing on the 162 Amax this week. I'll post the results after I'm finished.

I know the 180 7mm JLK bc is high so I'd say the 168 will be as well.
 
#3
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

The JLK BC is inflated as is probably the AMAX. Luckily, Brian Litz is Berger's ballistician and there BCs are right on the money as tested on the rifle range. If you read the articles on his website Applied Ballistics you will get the skinney on BC testing and the computational errors created. In short, you have to test the on the range. When he tested the 180 JLKs that had a claimed BC far higher than the 180 Bergers they both shot exactly the same. He wrote about that in Precision Shooting Mag.

It is not that bullet companies are necessarily attempting to dupe you. He notes that some ballistic measurement programs induce 10% or more error at times. If the model isn't exactly correct you are not going to get the correct BC.

You should also purchase his book off the website. It should be required reading for all shooters. That Berger BC you listed is most likely within +/-.003. I think it is safe to say that the others are fairly inflated.

I have no affiliation with Berger or Brian. I shoot Sierra 175s in my 308. He is just one smart man and actually gets out and does the testing.

Josh
 
#4
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

i found the 162 to be somewere between .61 and .60. i used the higher of the 2 and it worked well for shooting steel only problem is when the plate is 12"x12" you could be alittle high or low and not know when shooting past 500yds, but for us a hit is a hit, you just want it repeatable.
 
#5
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

I'm of the mindset that Bryan has done the testing and published it in his book. Just like quickload data we're not supposed to discuss publicly here, I won't divulge the actual numbers. You can use the (Litz) data in JBM to get true numbers on the Berger and Amax.

If Mr. Litz is open to revealing these values directly it's up to him, but without expressly asking him, I'll refrain from doing so.
about 4-6% higher than actual, and the JLK value is very high but I don't remember the true value off the top of my head.

The 180 JLK is very close to the 180 Berger VLD for actual value, as I recall the 168's are very close too.
 
#6
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

Agree with Bohem, use the Litz BCs in JBM to answer your questions.

I have not seen the Litz BC for the 168g JLK, but think it has the same profile as the 180g JLK just less lead, so is a little less than the 180g Berger VLD range if I remember correctly.

The Berger 168g listed BC is the tested BC, so it should be very close to actual.

The Amax listed BC is about 4% higher than the tested BC IIRC.
 
#8
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jcvibby</div><div class="ubbcode-body">Have these BC's been confirmed by anyone?

Swampwork JLK 7mm 168 VLD at .690
Hornady 7mm 162 A-max at .625
Berger 7mm 168 VLD at .617

Both the A-Max and the JLK are very good looking bullets for an average velocity 7mm caliber </div></div>

Perhaps most here are already aware of this, but one point to keep in mind is that these numbers are the manufacturers published <span style="font-style: italic"><span style="font-weight: bold">G1 BC</span></span> figures. The published G1 BC numbers reflect the highest possible value of BC for a bullet traveling at the highest velocity range, but BC numbers actually vary as velocity changes.

What this means is that one G1 number will not be correct over the entire velocity range that a bullet will experience during flight; so using only the <span style="font-style: italic"><span style="font-weight: bold">high</span></span> G1 number will not allow a ballistic program to output accurate drop and wind predictions; the resulting predictions will be optimistic.

However, the high G1 number is useful for making general comparisons of various bullets.

So for comparison purposes, yes, these 7mm bullets do have high BC values in the approximate correct range, and those are very good looking bullets for long range work; far better than say 30 caliber bullets of the same weight.

TC



 
#9
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Top Cat</div><div class="ubbcode-body">Perhaps most here are already aware of this, but one point to keep in mind is that these numbers are the manufacturers published <span style="font-style: italic"><span style="font-weight: bold">G1 BC</span></span> figures. The published G1 BC numbers reflect the highest possible value of BC for a bullet at the highest velocity range, but G1 numbers actually vary as velocity changes.

What this means is that just one G1 number will not be correct over the entire velocity range that a bullet will experience during flight; so using only the high G1 number will not allow a ballistic program to output accurate drop and wind predictions.

However, G1 is useful for making general comparisons of various bullets.

So by comparison, yes these 7mm bullets do have high BC values and those are very good looking bullets for long range work; far better than say 30 caliber bullets of the same weight by comparison.

TC
</div></div>

Not sure if we are on the same page. The G1 and G7 are actually drag profiles. The G1 is a standard military projectile drag function that many makers like to benchmark against and obtain there BC. The G7 is a more accurate drag function for boat tail bullets which we use almost exclusively on this site. However, because the benchmark drag model is a better match it also produces BC numbers that are about half the G1 BC. While the G7 is way more accurate for ballistic computations because it is constant for all velocities, most manufacturers like the G1 BC because it is a higher number.

The real issue at hand is that bullet makers with the exception of Berger only do testing on a computer model. This can lead to large errors (up to 10% or more according to Litz). His BCs for bullets are based off actually testing them on the range. Get his book, as there is a relatively exhaustive list of tested BCs for various bullets in there (other than Berger).

Ballistic Coefficient Testing by Litz

Litz Explains G1 and G7

This should all be required reading.

Josh
 
#10
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

Top Cat and MD-

The G1 is a flat based spitzer that stems from the early 20th century military small arms bullets. The G7 is a boat tailed spitzer that stems from models created for artillery shells.

The G7 drag coefficient changes as velocity changes as well, it's just that our long, heavy for caliber BT match bullets are well compared to the G7 standard curve than the G1 standard curve.
 
#11
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">The G1 is a flat based spitzer that stems from the early 20th century military small arms bullets. The G7 is a boat tailed spitzer that stems from models created for artillery shells.</div></div>

Just as I stated. They are two different drag profiles. I even included the second link to explain the difference. Brian Litz is a bit more exact when it comes to that.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">The G7 drag coefficient changes as velocity changes as well, it's just that our long, heavy for caliber BT match bullets are well compared to the G7 standard curve than the G1 standard curve.</div></div>

This is inaccurate. If you would read the second link you would see where Brian Litz clearly posts, in italics and bold I might add, the following

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Brian Litz</div><div class="ubbcode-body">As you can see, the G7 standard projectile, with its long boat tail and pointed ogive bears a much stronger resemblance to a modern long range bullet than the G1 standard projectile. <span style="font-weight: bold"><span style="font-size: 14pt">As a result, the BC of a modern long range bullet that’s referenced to the G7 standard is constant for all velocities!</span></span> In other words, a trajectory that’s calculated with a ‘G7 BC’ doesn’t suffer from the same velocity dependence problems and inaccuracies as calculations that are made with a G1 BC.</div></div>

Josh
 
#12
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

I've been wondering about these for a while now:

http://www.gsgroup.co.za/308197SP204.html

Being a hunter shooting a 30-06 with 1:10 twist tube, I'd like to shoot their 177gr bullet also (following link) if it measures up properly. It has a company-advertised BC close to the AMAX and other 210g class bullets, but 30g less weight for velocity. Sounds perfect for me if it wasn't so darn expensive:

http://www.gsgroup.co.za/308177HV198.html
 
#13
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

Josh,

I appreciate your efforts to clarify the G1/G7 standards. However I have to apologize for my lack of clarity in the above quote that you used.

What I intended to convey is that modern bullets are more consistent with the G7 standard than the G1, and that BC's referenced to the G7 standard are <span style="font-style: italic">more</span> consistent over a range of velocities compared to BC's referenced to the G1 standard.

My error in wording could mislead one to think that the G7 BC of a modern bullet doesn't change <span style="font-style: italic">at all</span> with velocity. That's not true. The G7 BC of a modern bullet will change slightly with velocity (much less than a G1), but unless the bullet is shaped exactly like the G7 standard projectile, it's G7 BC will change slightly with velocity.

Keep in mind that referencing the G7 BC will remove 90% to 95% of the velocity dependence of a G1 BC, but it doesn't <span style="font-style: italic">totally</span> eliminate it.

Again I apologize for my lack of clarity which put you at odds with bohem.

Take care,
-Bryan
 
#15
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

Bryan-

Thank you for the clarification and help.

Tim-

Those are a monolithic solid as I recall. They're going to have excellent long range characteristics but they would not be my first choice for a controlled expansion hunting bullet. If you're wanting to use them for that purpose I would suggest getting in contact with GS Customs, I believe his name is Gerard Schultz on this forum as well.
 
#16
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

thanks guys, Where are the test results for the 162 amax. I found bryan's results for both the 168 and 180 VLD bergers but could not find his actual test results on what the correct, tested BC is for the AMAX. ??????? THanks guys and take care
 
#19
Re: ARE THESE 7MM BC's CORRECT AND TRUE???????????????

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jcvibby</div><div class="ubbcode-body">Thanks BOB, thats perfect. That 7mm 162 AMAX seems tough to beat out of a .284 Win...... </div></div>

I believe the 180g Berger Hybrid is the bullet to beat in a .284 Win.
 
You must log in or register to reply here.

Similar threads

P
7-08 vs 7 SAW vs 7CM vs ? for Large Frame
Replies
29
Views
2K
Qpski
Q
T
7X300WM- Heavy Bolt Lift only on Fire Formed - Need to Neck Turn?
Replies
9
Views
331
Maurygold
M
T
New to non SAAMI Loads- 7x300Win ANY/ALL advice needed and greatly appreciated.
Replies
21
Views
587
Schw15
S
K
SOLD 7MM Bullets _ updated
Replies
3
Views
572
Kramer93
K
A
Bullets with shortest jump to lands, AR 308 gas guns
Replies
10
Views
833
nn8734
nn8734
Top Bottom
Back
Home
Forums
Merch
Alerts