WEIGHING BULLETS AND ACCURACY

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  • Last Post 29 January 2018
joeb33050 posted this 28 January 2018

 

WEIGHING BULLETS AND ACCURACY

 

“Accuracy”, here, is the region between .5” and 1.0” large sample 100 yard 5-shot groups.

 

 

 

When accuracy is important, cast bullets should be visually inspected and those with major defects put aside. Some of the remaining “good” bullets will have minor defects. The definition of “major” and “minor” is in the eye of the inspector. There is some evidence that smaller visual bullet defects do not cause inaccuracy.

 

 

 

Visually acceptable cast bullets are sometimes weighed. Weighing bullets identifies outliers and allows them to be separated. As an example, a certain set of bullets had the following weights, in grains:

 

52.9/1, 54.2/2, 54.8/9, 54.9/12, 55.0/55, 55.1/5.

 

The 52.9 and the two 54.2 grain bullets are obvious outliers.

 

 

 

If we assume that difference in bullet weight causes difference in height, elevation, of the bullet at the target, we might put these three bullets aside.

 

(Reasonable differences in bullet weight causes insignificant changes in velocity, and in elevation. See below.)

 

 

 

We assume that difference in bullet weight is caused by holes in the bullet, and, if we assume that these holes affect accuracy; then we might put these three bullets aside. (We do not assume that the density of bullet material varies.)

 

 

 

We’re left with these bullets:

 

54.8/9, 54.9/12, 55.0/55, 55.1/5

 

We could segregate these into four classes, or 3, or 2, or make them all one class. The fundamental question is: What is the relationship between variation in bullet weight and accuracy?

 

 

 

Well cast 200 grain bullet weights have a standard deviation of about .125 grains.

 

We would expect the average of a lot of batches of 100 to weigh about (R.E.):

 

 

 

199.7   1

 

199.8   5

 

199.9   16

 

200.0   58

 

200.1   16

 

200.2   5

 

200.3   1

 

 

 

And the fundamental question turns into:

 

What is the relationship between group size and the myriad of combinations of bullets of various weights? EX: 5 @ 199.8 vs. 5 @ 200.0, 5 @ 199.8 vs. 5 @ 200.2, 5 @ 199.9 vs. 5 @ 200.1…

 

 

 

Here is a method:

 

 

 

TESTING CARTRIDGE VARIATION AND ACCURACY

 

There are 2 furthest-apart holes that determine group size.

 

We wish to know if some variation in one cartridge, of five, increases group size with 5-shot groups.

 

Group size is the distance between the two furthest-apart holes in the target; call the holes A and B.

 

Call the hole made by the cartridge with variation, V.

 

The probability that A = V is .2; 20% of the groups will have A = V.

 

80% of the groups will not have A = V. This 80% has one of the holes = A; 1 of 4 = 25%; 25% of 80% of the groups has V = B.

 

The summed probability = 20% + (25% X 80%) = 40% of the groups shot will have either V = A or V = B.

 

If % A or B = V > 40, then the variation probably increases group size.

 

If % A or B = V ~ 40, then the variation probably does NOT increase group size.

 

If % A or B = V < 40, then the variation probably reduces group size.

 

 

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joeb33050 posted this 29 January 2018

 

I then prepared sets of 30 WCF cartridges with 314299 bullets; one set with perfect bullets, a set with .2 grain filed off, and a set with .5 grain filed off. Here is a picture of 314299 bullets with .5 grain round-filed off.

 

 

 

 

Winchester M54. 30WCF, 30X Lyman STS

 

The load is:

 

314299 "No Dot", GC Alox lube, WLP, 12.5/AA#9, LOA 2.845"

 

 

 

"Perfect" bullets, Hard, cast 2/3/07, 199.4-200.2 gr., sized .309"

 

 

 

- 1/2 grain bullets, same as above but 1/2 grain filed off as shown

 

 

 

-.2 grain bullets, cast 3/9/07, 194.7-195.0 grains, sized .312"

 

 

 

 

 

On Wednesday, May 16, 2007 I shot these test "filed-side" bullets at 100 yards, 2 foulers and 2 5-shot groups per 15 minute relay, alternating between the 3 test loads. Groups measured to the nearest .025" with a plastic ruler with .1" increments.

 

Unfiled, "perfect" bullets: 1.4", 1.5”, 1.95”, and 1.475”, 1.825 “Avg. 1.63"

 

Bullets with .2 grain round-filed off the side: 2.2", 1.35", 1.2", 1.95", 1.275” Avg. 1.595"

 

Bullets with .5 grain round-filed off the side: .95", 2.75", 1.175", 3.15", 2.5" Avg.  2.105"

 

I'm a little surprised at the "perfect" bullet groups; the 412 5-shot groups I've tested with this rifle and many powders/several bullets have averaged 1.466".

 

This data and last weeks data suggests that variations in bullet weight may cause variations in accuracy; and that bullets with bubbles/holes may be less accurate than those without.

 

All going toward the "Weigh bullets" question.

 

 

 


            I repeated the tests on 5/23/07 and 6/20/07. Here is a table showing the results of the here tests:

 

 

 

 

Perfect

Filed .2 gr.

Filed .5 gr.

5/16/2007

1.400

2.200

0.950

5/16/2007

1.500

1.350

2.750

5/16/2007

1.950

1.200

1.175

5/16/2007

1.475

1.950

3.150

5/16/2007

1.825

1.275

2.500

Average

1.630

1.595

2.105

%

100.0%

97.9%

129.1%

5/23/2007

1.300

0.900

1.750

5/23/2007

1.700

1.750

1.300

5/23/2007

2.000

1.300

1.250

5/23/2007

2.100

2.150

2.050

5/23/2007

1.800

2.050

1.150

Average

1.780

1.630

1.500

%

100.0%

91.6%

84.3%

6/20/2007

1.450

1.900

2.400

6/20/2007

1.950

1.975

2.050

6/20/2007

1.450

1.750

2.450

6/20/2007

2.350

1.350

2.425

6/20/2007

1.750

2.800

1.250

Average

1.790

1.955

2.115

%

100.0%

109.2%

118.2%

Grand

 

 

 

Average

1.733

1.727

1.907

%

100.0%

99.6%

110.0%

 

 

 

Group sizes were measured with a plastic ruler graduated in tenths of an inch.

 

Resolution of group size was to .025" increments. All three-place decimals were formatted for consistency and ease of reading.

 

These three sets of groups were shot on three different days under three different sets of conditions.

 

If the grand averages are an indication of the process, then there is no "real" difference in group size for groups shot with "perfect" bullets and bullets with .2 grain round-filed off; and there may not be a "real" difference in groups shot with perfect bullets and bullets with .5 grain round-filed off.

 

In order to confirm that there is a difference in accuracy between "perfect" and ".5 grain" bullets, with 90% confidence, 28 groups with each bullet would be required. For 95% confidence, 47 groups, each, would be required. Now these groups should be shot with bullets, powder, etc. from the same lots, under the same conditions. I'm not going to do it, and suggest that the results of this test can be summarized as follows:

 

"In gun/load/etc. systems with capability to shoot 100 yard groups averaging 1.75" or greater, filed grooves on the sides of the bullets of up to .5 grain simulating holes only slightly increase average group size."

 

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joeb33050 posted this 29 January 2018

 

DAMAGED 22 RIMFIRE BULLETS          

 

Here’s a picture of 22 RF bullets with .3 grain filed off.

 

Cartridges were prepared with .1 and .3 grains filed off with a triangular file.

 

On 6/27/2007, Model 12/15 BSA Martini, Lyman STS 30X, 50 yards, windy and starting to rain in fits.

 

Perfect, .1 grain filed, .3 grains filed ammunition.

 

This gun, like the rest, loves Eley Match ammunition.

 

I was going to file some Eley Match Red Box, I had the file in one hand and the first cartridge in the other, but a force stronger than I, (and I am enormously strong), kept me from touching that Eley cartridge with the file.

 

I was able to file the PMC Match Rifle, this ammunition works well in this gun.

 

Group sizes, leaded edge to leaded edge - .244", all in "

 

Perfect -.1 gr.   -.3 gr.

 

.433     . 473    .353    

 

.382     .564     .324

 

.439     1.294   .394

 

.419     .732     .546

 

.547     .443     .910

 

Avg.    Avg.    Avg.

 

.444     .699     .505

 

Here's the target:

 

As an aside, thirty cartridges had an average weight of 51.9 grains and a standard deviation of .228 grains.

 

Thirty empty cartridge cases had an average weight of 9.8 grains, and a standard deviation of .07 grains.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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joeb33050 posted this 29 January 2018

THE ABOVE ARE FROM CHAPTER 3, CAST BULLETS FOR BEGINNER AND EXPERT, 3RD ED.

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