BC for JLK 6.5/130's

Ratbert

Ratbert

Gunny Sergeant
Full Member
Minuteman
Jul 18, 2007
2,341
1
48
Concord, NC
#1
Anyone have a G7 (or even a good G1) BC for the 130gr 6.5JLK VLD's? They're listed as 6.20 G1 with a '?' on the swampworks page so I was hoping someone might have something they'd worked out a little more definitively. Unfortunately Bryan only lists the 140 in his book.
 
#3
Re: BC for JLK 6.5/130's

They are terrible....I hope you didn't just buy like 1300 of these crappy bullets....that would suck.

wink.gif
 
#5
Re: BC for JLK 6.5/130's

I started shooting the 130s. If you enter the BC of .620 and a G1 your dope will be off. I played with my program and entered .350 G7. Everything matches up from the field data of my gun shooting. Try this number and shoot. It should match up with your data. Try it and see. Post your results
 
#6
Re: BC for JLK 6.5/130's

So I just had this discussion with someone on the net that I respect in regards to BCs on this bullet (to be remained nameless). His opinion was that since the 130gr and 140gr bullet have the exact same stated dimensions, the BC of the 130gr should very closely approximate the BC of the 140gr.

I'm just starting to work up a load for the 130s as well which is what prompted the question. I don't have any more empirical evidence at this point unfortunately but the above logic will be my starting point.

One other thing I noted is that when measuring the 130gr, I found the dimensional spec to be off what is posted on the JLK website. My 3 different batches (bought them from 2 others before my main batch came in), all came in at an OAL mean of 1.3565" with a max of 1.3615" and a min of 1.3535" after measuring 20 random bullets from each of the 3 batches. Fairly consistent dimensions but this is shorter than the specs on the web and in Litz's book.

Also, the length to ogive (LTO) averaged .6168" with a maximum of .6175" and a minimum of .6160". Also fairly consistent but shorter than the stated specs.

All the above data leads me to conclude the BC will be below the 140gr (if indeed the 130gr bullet differs in length from the 140gr) but only a little testing will solve this hypothesis......... Unfortunately I don't have any 140gr bullets to compare against otherwise I would run the same measurements.
 
#7
Re: BC for JLK 6.5/130's

I shot the load yesterday. My 26" krieger 260 shoots the 130s and the 139s at 100 yards dead nuts the same. Why I don't know. When I step out to 800 yards shooting yesterday. I shot 5 of the 130s and the come up was 16 moa and then shot 5 139s the come up was 18.8 moa. The 130s I'am getting more speed with less pressure.

130s =2950 fps

139s=2840 fps

Both are just as accurate as the other. The measurements on the 130s was very consistent. I think this is one of the most accurate loads I have loaded. Wish there was a publish G7 for the load. I can't tell the difference between the 130s and 140s. I do think the numbers for the G7 I listed above is close for my rifles. The data matches to the actual shooting data. I'am no genius , but the numbers did work.
 
#8
Re: BC for JLK 6.5/130's

If everything else is held constant, the lighter bullet will have a lower BC because it's related to the sectional density of the bullet, which is based upon the bullet weight.

If you have a bullet with an identical outside shape, but change the core weight from 140 to 130 grains, the 130 will be close (form factor will be the same) but the sectional density decreases by 130/140=0.9286

The BC = sectional density / form factor, so theoretically you'd see about 7% reduction in the BC.

The increased velocity that you can get from these bullets should be helpful since there's a very small reduction in BC.
 
#9
Re: BC for JLK 6.5/130's

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dar</div><div class="ubbcode-body">I started shooting the 130s. If you enter the BC of .620 and a G1 your dope will be off. I played with my program and entered .350 G7. Everything matches up from the field data of my gun shooting. Try this number and shoot. It should match up with your data. Try it and see. Post your results </div></div>

.350 is really high dar. In fact higher than it's bigger brother the 140 which has a .327 G7 per Brian Litz. Like bohem mentioned above, it should be something less than the 140.

I too fiddled around with the bc in my software and anywhere from .305 to .310 keeps me within .1 mil of my real world dope.

Edited: I just read the last line of bohem's post, and I agree. I ordered a good quantity of the 130's primarily for my 6.5X47 since it won't push the 140's all that fast. I measured my 130's and they are right about 1.35 in length. The 140's that Mr. Litz used were 1.406.
 
#10
Re: BC for JLK 6.5/130's

If I enter the .310 bc for this bullet. It is almost 3/4 moa off of the real dope from the field. At 600 yds it calls for 9.8 come up and the field conditions is 9 come up. The .350 may be wrong but then why would the data match?

Enter this into your data.
260
130s JLK
600 yards 9 moa
800 yards 15 moa
3050 fps
30"barrel
These numbers shot in a match with another shooting my rifle. The G1 will be off and the G7 will be off unless you enter the .350 for the G7. This is the numbers I would use to match my rifle up to the data. Is this right or wrong?
 
#11
Re: BC for JLK 6.5/130's

What kind of scope do you use, and have you ever checked it's tracking? I mean actually checked that it moves the amount advertised per click? Thats the only thing that could explain it. There is no way it has a .350 G7...thats higher than just about anything but turned solids and the 300gr .338 bullets.
 
#12
Re: BC for JLK 6.5/130's

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">If everything else is held constant, the lighter bullet will have a lower BC because it's related to the sectional density of the bullet, which is based upon the bullet weight.

If you have a bullet with an identical outside shape, but change the core weight from 140 to 130 grains, the 130 will be close (form factor will be the same) but the sectional density decreases by 130/140=0.9286

The BC = sectional density / form factor, so theoretically you'd see about 7% reduction in the BC.

The increased velocity that you can get from these bullets should be helpful since there's a very small reduction in BC. </div></div>

Yes, of course you're right which is why I mentioned that this was a starting point to work back from.

After looking back into my ballistic coefficient data (a spreadsheet with G1s and G7s that I could find for my most popular bullets, I noted the formula for calculating sectional density.

SD = [ x / (7000 gr/lb) ] / [ y ]^2
x = grain weight of bullet
y = caliber of bullet

So to compare the 140gr and the 130gr.

140gr with Litz G7 BC of .327
.287 = [140/7000]/.264^2

130gr
.267 = [130/7000]/.264^2

At this point, I'm not sure how to determine a calculated G7 BC. Maybe somebody else can chime in to take the calculation further.
 
#13
Re: BC for JLK 6.5/130's

I use a 4x16 S&B P4 fine.

I do understand what you are saying about the bullet. But who is to say the bc isn't high. I'am getting 3050 fps out of this rifle and 2950 out of the 2nd 260. The BCs work with both rifles.
 
#14
Re: BC for JLK 6.5/130's

I am surprised Mr. Litz has not jumped into the conversation yet regarding these 130's. As per his book, you need to calculate the form factor of the 130 first before you can figure out the G7 BC. I won't type out the whole equation but start with:

Equation 17.1 pg. 532: G7 form factor prediction. It's long and tedious and requires alot of measuring. Then,

Equation 2.1 pg. 523: the ballistic coefficient.

I think this will yield close results, but haven't done the math myself so... have at it.
 
#15
Re: BC for JLK 6.5/130's

I'am not a math guy. I shoot and find the results from shooting. I do chrono the load for SDs. The data should match up within a 1/4 moa. It should not be off by 1 moa. The numbers of the .350 does work. If you shoot these bullets. Try shooting them at 600 and 800 seeing what numbers you come up with.
 
#16
Re: BC for JLK 6.5/130's

Swan, I'll take a look at the book when I get home, since I don't have it at work.

My point was that the bullets come from the same die, they just have a different core weight, so the only difference in the formula is the actual secional density. Doing all the math is not necessary for the form factor because it's the same as the 140.

Since we have a real world measured G7 for the 140, and they have "identical" shapes then we know what the form factor is for the 130 as well.
 
#17
Re: BC for JLK 6.5/130's

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">Swan, I'll take a look at the book when I get home, since I don't have it at work.

My point was that the bullets come from the same die, they just have a different core weight, so the only difference in the formula is the actual secional density. Doing all the math is not necessary for the form factor because it's the same as the 140.

Since we have a real world measured G7 for the 140, and they have "identical" shapes then we know what the form factor is for the 130 as well. </div></div>

if they have the same form factor as you claim, then:

G7 = (130/7000)/((.264)^2*(.878)) = <span style="color: #CC0000">.<span style="font-weight: bold">303 to .304</span></span>

also which jives with bohem's approximation of a 7% reduction in BC from the 140's, its actually about 7.7%
if my math is correct
smile.gif
 
#18
Re: BC for JLK 6.5/130's

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Swan</div><div class="ubbcode-body">
if they have the same form factor as you claim, then:

G7 = (130/7000)/((.264)^2*(.878)) = <span style="color: #CC0000">.<span style="font-weight: bold">303 to .304</span></span>

also which jives with bohem's approximation of a 7% reduction in BC from the 140's, its actually about 7.7%
if my math is correct
smile.gif
</div></div>

Can you simply multiply the sectional density by the i7 factor of .878 to get a G7 BC? I thought it was more complicated than that?
 
#19
Re: BC for JLK 6.5/130's

Swan,

I just re-read your earlier post referencing the formula in the back of Liz's book. Sounds like the i7 factor in the denominator will give you the G7 BC (or the G1 BC for that matter if you use the i1 factor).

Fascinating! I really need to sit down and read Litz's book from beginning to end!

So I'll also load up a few and shoot them on the 1K range to test out the predicted .304 G7 number.

I agree though, .350 seems realistically too high. Dar, I think you need to account for density altitude in your dope chart. What elevation, temperature, pressure, and humidity were you shooting at? I can calculate a DA number to keep the discussion an apples to apples one.
 
#20
Re: BC for JLK 6.5/130's

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hazardus</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Swan</div><div class="ubbcode-body">
if they have the same form factor as you claim, then:

G7 = (130/7000)/((.264)^2*(.878)) = <span style="color: #CC0000">.<span style="font-weight: bold">303 to .304</span></span>

also which jives with bohem's approximation of a 7% reduction in BC from the 140's, its actually about 7.7%
if my math is correct
smile.gif
</div></div>

Can you simply multiply the sectional density by the i7 factor of .878 to get a G7 BC? I thought it was more complicated than that? </div></div>

No, because that would yield a value of (.267)(.878) = <span style="color: #CC0000">.234</span>, to get the correct value you must divide the sectional density by the form factor: (.267)/(.878) = <span style="color: #CC0000">.304</span>

So, two ways to derive the G7 BC.
 
#21
Re: BC for JLK 6.5/130's

Yep, got it. Multiply the denominator to calculate the derived G7 or G1 BC. Very nice. With this calculation, we can now derive any BC from sectional density calculations it would seem.
 
#22
Re: BC for JLK 6.5/130's

Here is the numbers from the area. 1325 altitude ,29.92 pressure,temp31.The humidity was high due to snowing. I did not do density. I also shoot at my house and the numbers was the same. I would agree with getting this numbers but most of the time shooting under 800 yards the numbers does not have enough in change from the small changes. My dope did change only because of the angle of the shot. I do understand that. I had the person adjust an 1/2 moa for the hit.

Shoot the 130s and use a .350 for your G7 and see where you hit. Then shoot using the .304 and see where you hit. Then report your progress.

Here is the load
JLK 130s
NOS brass
o-give 2.333
BR2 primer
RL-17 45.5 grs (hot)
3050 fps
SDs 7
 
#23
Re: BC for JLK 6.5/130's

Interesting, I was going to guess that you were somewhere high which would explain your higher G7 estimate without taking into account density altitude.

Per your data and a 30% estimated humidity, your DA is -228ft.

So much for guessing that you lived in the mountains! ;>
 
#24
Re: BC for JLK 6.5/130's

I live in Nebraska. I shot the gun with the same results in the 2 areas. I shot in Missouri at the Big Pinney Match last weekend. The dope was the same. The altitude there was 1328 and mine is 1785. It was not enough to make a difference to change the dope.
 
#25
Re: BC for JLK 6.5/130's

Very interesting for sure. I'm looking forward to testing them. I'm hoping I have the same results as I have a 260 Ackley that will surely be a 1K screamer that will outshoot these 243 Win guns that keep working their way up the rankings at out local matches!
 
#28
Re: BC for JLK 6.5/130's

My 26" 260 shoots the 130s and 139s with the same 100 yard zero. But when you step out to 800 yards there is a 3 MOA difference. A buddy of mine shot it in Missouri and is building a 260 now. He is sold on this load. Shoots like a laser.

One thing I had to do was change the neck tension on my die. I was using .288 and went to .286.
 
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