168 vs 169 no load data

mehavy said:
Real men shoot`06s.
(and Garands)
Click to expand...

Actually, the Garand was one of my first thoughts, as the closed tip will resemble FMJ for historical correctness. Rest assured, I will be testing in one of those as well as in the .308.
 
Midway at least has some. Just about everything else they sell is listed as out of stock, no back order.
However, as mentioned, 1 grain won't make any difference. Kind of makes you wonder what Sierra is thinking.
1,000 yards out of a .308 is better done with a 175.
 
This bullet is very specifically intended to be fired from .308 Win at 1000 yards. It allows for a touch more powder and velocity from .308 cases and has a 4% higher ballistic coefficient than the 175 (assuming they are measured and reported the same way). The boattail matches the 175 so it won't get into the transonic dynamic stability problem the 1950s 168-grain SMK design does. From the photos, it appears the ogive is longer than the 175 and the bearing surface does not appear shorter, so I expect there is more hollow space in the nose. I will know more when I get them. I was able to order 500 from Creedmore Sports four days ago, but they show they are out of stock now.
 
In the 1980's Sierra changed their 30 caliber 180 grain HPMK boattail from 9 to 13 degrees to match the 168 HPMK's shape. The military teams rebulleting M118 match ammo with them watched them go subsonic before 1000 yards. They contracted Sierra to make a few thousand with the original 9 degree longer boattail like the 190 and heavier HPMK's used.
 
T. O'Heir said:
Midway at least has some. Just about everything else they sell is listed as out of stock, no back order.
However, as mentioned, 1 grain won't make any difference. Kind of makes you wonder what Sierra is thinking.
1,000 yards out of a .308 is better done with a 175.
Click to expand...
Best I've seen was 250 grain HPMK's leaving 2150 fps from a 1:8 twist barrel.
 
My dated Hornady book has 10 x 150-155 gr. bullets all listed with the same identical loads.

Configuration is from FB Lead tip to a GMX that is as long as the Bismark 15 inch gun rounds as well as a FB round nose lead tip.

If you want exact you are in the wrong hobby.
 
So I got the bullets in. I would not classify these as closed nose or similar to FMJ, definitely OTM. But I'm not complaining.

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I just got the news that my order never shipped and they don't have stock to fill it, so, regardless of what the site said, these are in short supply, too.

That's a good image. You can see the short conical narrowing near each tip. This is what a pointing die does and, apparently, they are calling that closing the tip. I would call it pointing the tip. It's a little like buying brass with a case prep step already taken.
 
Well, I weighed them all too.... That was tedious.
High 169.2
Low 168.7
Es 0.5g
Average 168.99
SD, I tried to calculate it, it said 0.10314. That does not seem right to me somehow though, long day.

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Last edited:
Put the bullet parameters into QuickLoad and (no surprises) QL nailed it.
(I would check your Distance-to-Lands* though)

5 Rnds just for the heck of it at 100yrds last night:
Garand-169-SMK-HPBTCN-4595-47gr-sm.jpg


Bottom Line: (after checking *D2L) treat it mostly like the 168.
 
One of the advantages of moderator privileges is I could go in and copy your data to paste it into Excel to check your SD calc for you. You got it right. My numbers are:

Code: 
Mean	168.99 grn
SD	0.10314 grn
MIN	168.70 grn
MAX	169.20 grn
ES	0.50 grn
I suspect the reason you thought the SD looked wonky is there is a rule of thumb a lot of shooters use that the ES of a normal distribution should be about 3 times the SD, and you can see your ES is more than 3 times the SD you arrived at. However, that rule is only applicable to a sample size of 10. It is also only true on average and is usually off some because the extreme spread is determined by just two samples out of the data, and it will be further off if an outlier shows up in the data. For a sample size of 100, ES is normally about 5 times the SD. In your case, multiplying the SD by 5 gives an expected ES of just under 0.52 grains. Pretty close to the actual 0.5 and about as good as you can expect from an estimate based on a sample of just the two furthest apart examples.

Remembering it is only true on average, these are the multipliers for other common sample sizes shooters use. To estimate ES from SD, multiply SD by these values, and (more common) to estimate SD from ES, divide ES by these values:

3 shots: 1.7
4 shots: 2.1
5 shots: 2.3
6 shots: 2.5
7 shots: 2.7
8 shots: 2.9
10 shots: 3.1
15 shots: 3.5
16 shots: 3.5
20 shots: 3.7
30 shots: 4.1
50 shots: 4.5
100 shots: 5.0

I have the number to two more decimal places, but nothing you measure will be likely any more accurate than you get with these two-digit numbers, so I just left it at one decimal place. Also, using this method with large samples has reliability issues because the more shots you fire, the more chances are you will have an outlier in the mix. As a result, there is an optimum accuracy point for the method, and that turns out to be with a sample size of 7. Below that number the real center of the group is uncertain. Above that number, too many chances for outliers are being allowed for best accuracy.


This paper explains where the multiplier numbers come from if that interests you.

This paper explains where the optimum size of 7 comes from, if that interests you.
 
Yep, it surprised me when I first saw it. I knew there was a point of diminishing precision for group diameters because of increasing outlier probability with shot-count, but hadn't attempted to calculate for a minimum and didn't realize it was that small. So, you could shoot 6 groups of 7 and get radial SD within ±15% by averaging their extreme spread and dividing that average by 2.7 from my table above (2.704 from the table linked to in the other article, but going to that many decimal places just tends to fool the user into thinking his answer is more exact than it actually is).

Despite 7 being the magic number, I think Kolbe is right that 5 shots is more practical for most people and shooting 9 groups of 5 (45 shots total) instead of 6 groups of 7 (42 shots) is so close in shot count that it will work out for them. In that instance, divide the average result by 2.3 to estimate radial SD.

If you want to use a single large group to better estimate SD, you need to know where every hole has landed. If you can locate each hole, and not just the two furthest separated holes, a quick glance (don't hold me to this) says about 12 shots should get you to 15% accuracy, whereas you need 42 shots total with the 7-shot groups. 12 is the same number of pairs of holes the 6 groups of 7 give you to evaluate, but that match in hole count doesn't work with the other group sizes, which need more because they are less efficient. And for someone shooting bugholes, knowing each shot's location is impractical to achieve without separate targets for each shot or an electronic target that accurately reports the individual points of impact.
 
The biggest (and most well-kept) secret to success
in any situation is that almost magical capability to
determine what is ... (drum roll please...) . . . . .

"Good Enough"

;)
 
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