Raimey;
I took the 707.7 figure from a metals table in a Machinery's Handbook, temp was not given, assumed standard ref.
Interestingly though the same chart gave specific gravity as 11.342. Calculating out this gives a lbs/ft^3 of 708.
Burrard states ""In proof Acts & Rules the dia's of all bores have been calculated on the basis of a specific gravity of lead of 11.352. So if N is the number of the "Bore" or "Gauge", & d the dia of the bore in inches we get:
d^3 = 4.6578/N""
He then gives a chart showing bore dia's from 4 through 32, which are the same as found in the proof house charts. If his formula is followed for all those sizes several "Miss" by .001".
If however the formula;
d^3 = 4.65148/N
is used, all sizes from 1 through 50 + those 16 sizes from; 51.05 through 172.28 fall within ±0.0005 (round to three place dimension)to exactly match the proof charts. This however gives lead a specific gravity of 11.364. Admitttedly no sizes will "Miss" by more than .001", which is insignificant. Since however a figure (range) can be found where every size fits precisely, I can only conclude they did calculate with the same accuracy & number of significant decimal places.
I even considered "Perhaps" they did not round but "Dropped all digits beyond three decimal places. No luck, no number could be found that would bring all gauges no larger than chart sizes by .001" without having a few drop by .001" to a smaller dia. I can thus only conclude they calculated to the same precision I am using but used a figure for lead heavier than the SpGr of 11.352 Burrard stated, even though at the time of his writing he undoubtably obtained this figure from a proof house. Definitely heavier than the 11.342 most present sources seem to indicate.
The point is though, even though so slight as to be of no practical significance, there is a slight variation which indeed exists.
The Specific Gravities would give dia's of a 1 lb ball as follows;
11.342 = 1.6704"
11.352 = 1.6699"
11.364 = 1.6693"
Proof charts give the lb ball (1 gauge) as 1.669".
Last edited by 2-piper; 05/26/08 11:00 PM.
