Weight Sorting FMJ bullets as an accuracy guide

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  • Last Post 25 January 2018
RicinYakima posted this 24 January 2018

 

Joe B’s Bullet Construction Test

 

First, I ran the outliers over my GemPro 250 electronic scale that weights in units of 0.01 grains.  Lightest was 54.92 grains and the heaviest was 55.90 grains. There was one at 55.61 grains that I culled from the group. From the mid-weights I sorted out five that were exactly 55.50 grains.

 

Visual inspection followed under a 4X glass. The easiest to see was that the lead core was not positioned the same. While on the outliers, they were from 0.030” below the base of the jacket, to flush with the base. The middies were from 0.030” to 0.005” below, measurements done with a depth micrometer. Next the bullets were inserted point first into an orifice 0.125” in a steel plate, and height measure of how much stuck up above the hole. The bullets with the most lead exposed on the boattail, also had the largest diameter ogive, and i.e. stuck up the least amount from the plate.

 

Using a micrometer with a 0.0001”, one ten thousandth scale, lengths were measured and all bullets were within 0.010”. Bullets were then measured above the cannelures and again below but above the beginning of the boattail. All bullets, even those with expanded ogive, were remarkably even at .2229” all around the bullets. However below the cannelure the bullets with lead all with way to the base of the jacket varied from .2229” to .2232” at random points around the circumference. Bullets with the lead at least 0.020” below the base of the jacket were .2229” below the cannelure.

 

Using a radius gauge, the base inside the boattail was measured. Bullets that had lead all the way to the base had inconsistent radii at least at one point around the circumference.  Bullets with deep seated cores had even radii. The angle of the boattail also varied as the more lead exposed bullets had about a seventy degree included angle while the deep seated cores were an even sixty degrees included angle.  

 

From the above observations, my hypothesis is that since the mass, weight, is the same, the cores of some bullets are seated to the rear of the jacket, therefore there must be voids in the front of the bullet.

 

This lead to sectioning 10 bullets: 5 from the middle of the population and 5 outliers. Bullets were milled to about 55% of bullet diameter. Jacket thickness at the ogive varied from 0.032” to 0.039” and point thickness was 0.065”. I was unable to determine if all jackets varied in thickness as the bullets were not strong enough to allow another 90 degree cut taken. However 6 of the jackets showed variations.

 

My hypothesis was in error, as there were no voids. What there was is a soft waxy material between the jacket and the core, soluble in alcohol. Researching how jackets are drawn from gilding metal discs, it appears to be from lubing the blanks as they are stamped out over several drawing processes. This wax was not evenly distributed around the cores but in one spot stretched out along the center line. Bullets with deep seated cores had no evidence of wax, the farther the core set back the more wax was in between the jacket and the core. I tried to dissolve the wax and then evaporate the alcohol, but the quantity was so small I did not have the apparatus to weigh or measure it.

 

None of my equipment could spin the bullets faster than 3600 rpm and at that speed I could detect nor measure any vibration or wobble. Rolling the bullets down a sheet of plate glass with a 0.20 feeler gauge under one side did produce an interesting effect. Bullets with deep seated cores and equal diameters above and below the cannelure would roll straight off the bottom of the glass. Bullets with lead to the bottom of the boattail would take a path towards the nose of the bullet until the bullet was perpendicular to the original path. I don’t know if that is because those had a slightly larger diameter below the cannelure or because they were heavier towards the base or because they were not balanced.

 

Bullets from the sample of 40 grain plastic tipped bullets were boring. The weight variations were 0.06 grains! Jacket thickness was 0.012” the same as a 22 LR case and even on the five cases dissected. None of my equipment or tests could discern any difference between bullets.

 

In summery my hypothesis is that:

 

1: weighting is futile

 

2: core placement in the jacket varies

 

3: because of manufacture, center of mass varies from center of form from back to front and around the axis of the bullet

 

4: sorting should be by how deep the lead core finishes up inside the jacket

I have many more pictures if interested.

 

Attached Files

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John Alexander posted this 24 January 2018

Wow! Nice careful work Ric.

It will be interesting if shooting indicate a significant difference in group size between groups of bullets sorted by depth of lead core and groups shot with unsorted bullets, and if so, whether small depth cores or greater depth cores are more accurate.

Were the bullets examined cheap AR fodder bullets or FMJ  name brand bullets?

Interesting data.

John

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RicinYakima posted this 24 January 2018

I have no idea, as they were a blind sample sent to me by joeb. I think these are the bullets that he has been shooting at cast bullet speed and loads. Since I don't own anything except a cheap M-4 in .223, I don't have anything to use them in. I already know that they will not work in my 1930's Savage 22 Hornet with 1/16 twist.

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RicinYakima posted this 24 January 2018

Measureing jacket thickness and using a comparator to see variations in boattails.

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Larry Gibson posted this 25 January 2018

Ric

 

Excellent analysis, it mirrors my findings in M80 and M2 bullets over the years.  I did sort by weight, by the core position in the bottom and by position of the canalure. I even melted the cores out to weight the jackets and found considerable variation. I then test fired them for group at 100 and 200 yards.  I found little if any improvement in accuracy.  Carefully milling the bullets it became apparent there is just too much variation in jacket thickness and even the interior for the core was not concentric to the bullet form.

I also test fired numerous different lots of M80 ball dating from '64 up through the early '90s.  I then pulled bullets from the most accurate and the least accurate lot.  Sectioning those bullets showed the most accurate had the least variation in all the discrepancies mentioned.  The most accurate lot was some TW68 which bullets had very uniform weight, consistent bases and uniform concentric jackets.  That lot, TW68, would shoot into very close to MOA out of my 14" twist Palma rifle and right at 1 1/2 moa out of my 12" twist M70 match rifle.

LMG  

 

Concealment is not cover.........

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joeb33050 posted this 25 January 2018

 

 

Jacketed bullets shoot much more accurately than cast bullets, and I’m trying to find out why. I’ve been shooting a lot of jacketed bullets at lower velocities. All .22 cal bullets, that stabilize, shoot accurately; except the .22 cal fmj cannelure bullets. These never shot accurately in the past, either.

 

 

 

 

The ARMSCOR 55 gr fmj cannelure bullets, three 5-shot 100 yard groups, shot very poorly.

 

 

 

Weights of the remaining 85 varied from 54.9 to 55.9 gr, clustering around 55.5 gr.

 

 

 

EX: Nosler 40 gr Varmageddon bullets weigh 40.0 grains, almost all. Data available.

 

 

 

If the BULLET determines accuracy, then there’s something about these ARMSCOR bullets that makes them inaccurate. 34 of them weigh 55.5 gr; I’ll shoot some of them to see if they’re accurate. But, I’d like someone to inspect/measure some of these outliers to see what’s different/off. Anyone?

 

 

 

joe b.

Armscor = inaccurate

Nosler 40 gr Varmageddon are the othere Ric got, accurate.

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Larry Gibson posted this 25 January 2018

Because the ARMSCOR bullets aren't balanced is the reason why.  They are, like most milsurp FMJs made to a lessor quality than commercial jacketed bullets these days.  Basically the center of mass is not coaxial with the center of form and thus not coaxial with the center of rotation.  It is nicely explained in Hornady Manuals.

LMG

Concealment is not cover.........

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