BULLET WEIGHT AND TESTING ACCURACY

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joeb33050 posted this 02 February 2018

 

BULLET WEIGHT AND TESTING ACCURACY

 

My take on Mann is that the spinning bullet, viewed from the shooter’s perspective,

 

rotates about a CENTER as it travels downrange;

 

and that CENTER rotates about the center of the resulting group.

 

Ric Baxter’s drawings, some comments here, and my experience as shown here, with large numbers of shots per group, support this notion.

 

Now we come to the method of testing to prove, beyond a shadow of a doubt, what the right-thinkers amongst us know to be true: that segregating bullets WITHIN a .4 grain range has no effect on accuracy.

 

Bullets that vary from -.4 to 0 grains shoot as accurately as those that weigh the same, on the alleged plateau.

 

One method is to shoot groups of 5 where 1 weighs .4 gr. less than plateauers, 4 at plateau weight.

 

Another method is to shoot groups at plateau level, and other groups at plateau-.4 grain level.

 

Given the Mann notion, what’s the best method?

joe b.

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RicinYakima posted this 02 February 2018

Joe,

I have been thinking about this hard the last few days (yes, I know that is dangerous). I can not come up with a test that would work because the bullet, as Mann states, rotates around of center of mass, i.e. the single microscopic point where the bullet has equal weight in all directions. So if the .4 grains is different from front to rear or closer to one side, their centers are different. That is without regard to total mass. If the .4 grains is a piece of doss hidden in the nose, the bullet will react differently than if the doss was in the rear driving band.

After three years of reading your arguments, you have convinced me that weighing just to put bullets into sets of equal weight is a waste of time. If they are on the bottom end of a bell curve, we know they are "missing" mass somewhere. If they are at the top of the curve they are missing less mass. On the plateau they are all equaling miss mass, but where is it in the bullet? Could be anywhere if we visually inspect them rigorously and the outside form appears perfectly equal.

In the 1930's L. E. "Sam" Wilson up in Cashmere, WA, made a machine to spin jacketed benchrest bullets 150,000 rpm. He did what we are doing, trying to see if he could test for the best bullets to shoot in a match. The most "stable" bullets shot no better or worse than the less "stable" ones. He said he simply didn't have equipment to measure the minute differences.

I beginning to think that you and Larry, John, Frank and 45 2.1 are equally correct in that we need to think out side the "box" but we can't define where the edges are on the box. We know that equal weights do not make the best groups, so we have to find some other criteria. And we have to be able to measure it and get repeatable results. But I don't know what it is.

This is making my head hurt, it must be martini time.

Ric

 

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Larry Gibson posted this 02 February 2018

Adding this to demonstrate/explain further how the different "centers" must coincide for best accuracy.  Any imbalance that causes the center of form, center of mass and center of spin to not coincide during the bullets flight causes a deviation from the intended flight path.

LMG

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

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RicinYakima posted this 02 February 2018

So how do we measure it? What equipment? Right now we shoot them down range and say "that one is out of the group must be bad". We need to know before hand,

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45 2.1 posted this 03 February 2018

Looks to me Joe already has a pre-determined result in mind. Without knowing what the distribution of anomalies are in the gullet, you can only guess at results. You also have the problem of bullet walking to get around. If you're interested in the concept of bullet walking.... then ask. I can tell you that you are leaving out a variable I've not seen taken into account.... here is a story to illustrate. A friend of mine has a Browning micro hunter in 22 Hornet which is very accurate with jacketed. With cast it has problems getting under 1 MOA with the normal distribution of bullets I see listed here. He also made molds at the time. He made a PB and GC of the same design for his rifle. Same problem except his shoot a lot better than the commercial molds. He started with normal weight segregation which improved it a little, but not to the jacketed standard. He then segregated by weight and diameter via micrometer. THAT solved his problem so now his daughter has a superbly accurate rifle that fits her and doesn't kick her. That rifle shoots 1/2 MOA pretty well on demand. Now, you have a way of improving the test... use it and find out for yourself.

As an aside, you will have difficulty seeing differences at 100 yards.....but those differences show up at 300 yards nicely. Increase the range and they show up more. You aren't going to do much of that until you're shooting a lot higher velocity with much better accuracy OR have a 1500 fps load that shoots 1/2 MOA and holds it at longer range.

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Ken Campbell Iowa posted this 03 February 2018

i think most any geeky high school electronics club member could make a spinner-detector now with the fun stuff available .... 200,000 rpm is easy with shop air ( g ) ...

but as per the last several weeks of comments here .... something is funny about the results of weighing.... and purposely unbalancing the castings ...  for slackers such as myself, it is not clear that even 1 grain voids are what gives me my 2 to 8  minute groups ....

i think mother nature knows exactly what is going on and is having a great time with her tease ...

*************

i am working on fully swaging my bullets ... but previous efforts with full swages did not result in 1/2 moa groups ... but did result in fewer wild fliers ...

just some thoughts

ken

 

 

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RicinYakima posted this 03 February 2018

45 2.1 ,

I would have to drive over 250 miles each way to find a 300 yard range I could shoot at. I am so old and crippled I can not walk through the sage brush 300 yards. That isn't going to happen. If I can not see and measure at 100, it isn't going to happen.

Ric

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RicinYakima posted this 03 February 2018

"i am working on fully swaging my bullets ... but previous efforts with full swages did not result in 1/2 moa groups ... but did result in fewer wild fliers ..."

Compressing doss isn't going to change much. How do you measure?

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45 2.1 posted this 03 February 2018

^^^^^^ My buddy told me he measured to 0.0001" on diameter and segregated within weights like that. Of course he removed the larger ones (differences in mold handle grip I would assume) to remove fliers. As far as ranges, I cleared the side of a field behind my barn and built berms at 100, 248 and 378 yards when I moved here. Pope and Donaldson gave precise instructions on how to use iron and aperture sights..... a dark covered shooting bench keeps glare off them and allows testing the rifle instead of playing games with ambient light conditions.

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John Alexander posted this 03 February 2018

45.2.1 wrote:

"You also have the problem of bullet walking to get around. If you're interested in the concept of bullet walking.... then ask."

========

45.2.1

I, and I am sure others as well, are interested.  It sounds bad so I am asking what it is and what have you found to get around it.

John

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Ken Campbell Iowa posted this 03 February 2018

here is an old target that might be interesting ... the top and bottom groups are fully swaged ....the middle is as cast, with gas checks.  might be interesting that the bottom group has no gas checks.  it is possible that the improvement is from the base being swaged square .  225438 little bees .  on the bottom group the lower shot chambered harder .

 

 

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45 2.1 posted this 03 February 2018

45.2.1 wrote:

"You also have the problem of bullet walking to get around. If you're interested in the concept of bullet walking.... then ask."

========

45.2.1

I, and I am sure others as well, are interested.  It sounds bad so I am asking what it is and what have you found to get around it.

John

Most rifles shoot repeatable patterns/groups as the barrel heats up in cadence fire of 40 to 60 second intervals... the tight bored military and most bull barrels do this with Unique loads at least. One has to have consistent loads for this, but you can plot by clock face time and distance from the aiming point for each shot. Many groups usually confirm the positions within a 0.1" position when you get things right. Holding off those positions can produce some very tight groups regularly. I've found at that time interval that thinner barrels heat too much and on the 7th shot they start up at about one thirty out of the group. Interesting to do at times, but it confirms barrel heating sequence.

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Ken Campbell Iowa posted this 04 February 2018

similarly we saw group center "" walking "" with our stiff short 1 inch diameter 20 inch 22 rf barrels  in br22 rf  ... and i think it was from barrel condition ... maybe ...ha ... from a * cold?  dry? non-sticky ? ??? * ...barrel the group center could be off 1 inch at 50 yards ... and if we didn't keep shooting about every 30 seconds the barrel /group would start walking .  generally always high when   ? cold ? ....  in these the barrel " walked " into a stable condition and you could shoot a hundred shots into the group if you kept going rapidy .

a pretty sharp cf br friend thought the vertical was because barrels droop as normally mounted.  i should have tried laying the barrel sideways and tried it.   we did remove, set back and rechamber,  and replace our barrels a lot, and the walking was mostly still  vertical .

it was rare that a barrel would put the first rf bullet in the group ..... but many mj barrels put the first * cold * bullet in the group .     so is it lubricant ??   tom grey talks about this phen-on-o-mem ......  oh, i found that k-mart lithium shot well after the first shot ... but that first shot could be a foot out of the main group ... amazing !! ... and if  i waited 10 minutes the next first shot was a foot away .... how could lube cause a good bullet to fly a foot away ??? .... 

if we grooved a mj bullet and put lithium grease on it would the first shot fly out a foot ?

ya gotta admit this isn't boring ...  ken

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John Alexander posted this 04 February 2018

I think most serious CB shooters shoot a fouling shot or two for that reason. There are exceptions. I think bore condition will be the answer to a lot of our tears if we ever figure it out.  Maybe change the ball game by using coated bullets?

John

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frnkeore posted this 04 February 2018

I think most serious CB shooters shoot a fouling shot or two for that reason. There are exceptions. I think bore condition will be the answer to a lot of our tears if we ever figure it out.  Maybe change the ball game by using coated bullets?

John

 

If only we could only use copper coated bullets

Frank

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