Thursday, April 14, 2011

Brass capacity Testing by -- Capt. Bob Peasley

From:  Capt. Bob Peasley:
     "Over the winter I started weighing brass into lots for better extreme spread control.  During those long lonely hours over the electric scale I wondered if it was really worth the effort.  Thus when it warmed up I began testing. 
April 8, 2011 was another dandy day to test some of the pent up ideas from a long lonely winter in Minnesota. It was 60 degrees, sunny and all bullets were moly coated, fired in a Krieger bbl. on a Stolle action. The bbl. has about 2250 rounds thru it at the start of testing. I weighed a bunch of 5 times fired WW brass over the winter and sorted into batches of about 1.4 gr. increments.  For reasons unknown to me I found about 10 pieces that were well above the highest average.  These 10 pieces averaged 171.5 gr. I picked 6 each of these and 6 of the lowest weight for testing. Results are shown below.
Read the results of Bob's testing--  Click Here

Hawkeye says:
   Over the years I have heard and read many opinions on case capacity vs velocity.  I have no doubt that there is a definite correlation between the two.  However, I am not so sure that there always is a correlation between the weight of the case and the capacity of the case.   Why not you say?
    Well, think of it this way.  Let's say you resize all your cases and then trim them to length.  You may or may not have taken off the same amt. of brass when you trim the neck to length.  So, therefore, even though the capacity may have remained the same from the shoulder down to the case head, the weight may no longer be the same for all the cases as you may have taken off a different amt of brass from the neck of each case, and then took off a little more when champfering the neck inside and outside.  
   Neck turning causes the same problem.  You won't take the same amt of brass off each case and therefore they will not weigh the same even if they have the same capacity.  Capacity equals internal volume, not weight. 
     Any other thoughts on this?   

1 comment:

Anonymous said...

Mass=Volume*Density. In order for you to use weight(mass) to correlate to internal case volume, you must assume that the brass varies insignificantly in density between cases and that the outside dimensions of your cases are identical (i.e. through sizing, trimming, turning etc.)If you are comfortable making this assumption and performing the steps to get your brass as externally uniform as possible, then weight variance between cases of identical external dimensions would represent a variance in case wall thickness, which by necessity given the above assumptions, would mean a change in internal volume.