Home Forums Hunting & Shooting Ask The Gunwriters Question about metric conversion

In my experience "thrown" measurements are acceptable at + or - 3 tenths of a grain. A good beam scale is certainly capable of better than that especially with stick propellants like any of the 4350's. I also use thrown/dipped charges with powders like IMR 4227 or BLC-2 but not 3031, 4350 or Reloader 22 type powders. The fourth figure is there virtually on all measurements with metric other than the exactly even ones. It occurs to me that I have seen metric data in the LEE Manual describing the use of their dippers. I dump the dipper into a scale and measure it out from there if I need precision.

The inch in the Imperial system is based on 10 so the 12 in the foot is based on inches which are based on the number 10.

That said I felt my earlier comment was unkind and unnecessary , I apologize.

They almost got the imperial system correct: 1 MOA = 1.047 inch.

So what's the end result? Did we all agree that the metric system was the better way to go?

Hell no because it is not, think about it no fractions and too many figures.

I still think in a mixture of Imperial and metric.

Weight in kg, speed in km/h but often mentally convert to mph, heights in feet and inches.

When I worked in oil exploration we would sometimes get a client that wanted all measurements in metric, so converted joints to m, gph, Barrels etc.

Trouble is, it was all USA not imperial, to metric. Here in Aus we were Imperial, but rigs were US. So short gallons, tons etc.

Didn’t the ship the USA metric rod get pirated to the Caribbean during the 19th century, and that’s why the USA didn’t go metric early on?

Not sure what you are trying to say there. A little reading on Wiki finds the following about an inch.

An Anglo-Saxon unit of length was the barleycorn. After 1066, 1 inch was equal to 3 barleycorns, which continued to be its legal definition for several centuries, with the barleycorn being the base unit.[14] One of the earliest such definitions is that of 1324, where the legal definition of the inch was set out in a statute of Edward II of England, defining it as "three grains of barley, dry and round, placed end to end, lengthwise".

and

In 1930, the British Standards Institution adopted an inch of exactly 25.4 mm. The American Standards Association followed suit in 1933. By 1935, industry in 16 countries had adopted the "industrial inch" as it came to be known.

As to CNC's: an inch based system typically has a resolution of .0001" as you mentioned. A metric system is typically .001mm. So which one is higher resolution?


Jerry

+1`

.001mm measures .000025 of an inch, or 25 millionths of an inch, also called a micron. To get a surface finish near a 25th of a 10 thousandth, or .000025 of an inch we would have to send the part out to grind as the surface finish on the part after machining in a lathe would be too rough to measure a micron. In fact I have no idea how you would measure a micron in a machine shop. That said I have never seen the micron symbol on a CNC lathe set to the metric measure. This illustrates the out of sync dimensions of metric. The micron being too small, the millimeter being too large so you have to break it down, the centimeter a semi useful measurement and the meter virtually never used. So yes a micron is smaller than .0001. That said if the machine can measure precisely enough for microns it can also measure .00001, however how a shop would measure the finished part to that tolerance I have no idea.

Just try to use your smart phone to add and subtract numbers over 6 figures! Rest assured you have to know how to use a calculator and the calculator has to be up to the task. Most phone calculators are just for dummies to check out their bank accounts.

Why is MOA 1.047? Who in their right mind would have done that?

Actually it doesn't. 0.001 mm is close to.00004".

Perhaps your problem is simply that the metric measures are simply unfamiliar?

We had a bit of that when metrication was introduced here. I was at school at the time, and so learned both systems, and so I don't have any difficulty with either of them. Metric is a great deal simpler though, especially when everything (or nearly everything) is metric and you don't have to worry about conversions any more. I can say that machinists here have no difficulty programming CNC machines in metric.

My phone will do fine with up to 9 figures. There again it is easy enough to use a pencil and paper for addition and subtraction.

Of course, the point's a bit moot really. How often do you really need to do those 6+ figure calculations manually at all?

The Sumerians? Hipparchus of Nicaea?

You do realise that it is a subtension of an angle?

A clear indication you don't know what a minute of angle is.

I prescribe 10ccs of metrication. Stat!

Ya, I think I rest my case !

Actually it doesn't. 0.001 mm is close to.00004".

It is a good thing you don't have to measure parts to that close a tolerance!


Well in reality 1 millionth of a meter comes out as .0000393, a micron measured by the inch comes out as .0000254


Perhaps your problem is simply that the metric measures are simply unfamiliar?

Sadly not true!

We had a bit of that when metrication was introduced here. I was at school at the time, and so learned both systems, and so I don't have any difficulty with either of them. Metric is a great deal simpler though, especially when everything (or nearly everything) is metric and you don't have to worry about conversions any more. I can say that machinists here have no difficulty programming CNC machines in metric.


I only said it takes longer even without the conversion factor. Added figures do not make punching keys less often.

Actually I have personally measured down to +/- less than a micron, and I have seen measurements performed to a higher degree of precision than that. You on the other hand have already said that you have no idea how you'd measure to those sorts of levels of precision, which rather makes a nonsense of your assertion:



Your assertion that 0.001 mm is not "close to .00004" but rather is .0000393" is a good example of false precision, or spurious precision, and it isn't the first example in your reasoning. Each of .001 mm and .00004" has one significant figure. They are an "apples to apples" comparison, where .001 vs .0000393" is not. .Another way of putting it is that if the best you can measure to is a hundred thousandth of an inch, it is spurious to report to a ten millionth, and nonsense to argue that 7 ten millionths makes any sort of difference. .