Quote: All this talk lately about "improved" cases has peaked my curiosity.
or has it peaked your interest in pot stirring.....?
actually if the goal is to plot a curve with a certain caliber and projectile weight starting with the powder charge in a .308 Winchester and follow it to the .300 Ultra mag.....I believe that can be easily done.....and it's data is available in almost any good reloading book that uses pressure barrels to attain their max velocity. If one leaves the data sets to the criteria of "flat looking primers and hard extraction" all you'll get is frustration and a flurry of new english words even my ex-wife hasn't used yet. It would be a worthy task.....and in theory anyone should be able to measure their case capacity in grains of water and then plot the max potential velocity for that case.
I'll help if you want to go for it.....I'll even put the curve on a calibrated board and post it here.
Posts: 28849 | Location: western Nebraska | Registered: 27 May 2003
7.5 x 7.5 = 15.5%Am I even close?? maybe I misunderstood,but 7.5x7.5 =56.25
Ray
Quote:
jb
I was leaving out the decimals and zeroes and other such. What I meant to say was 7.5% x 7.5%. I should have writ 1.075 x 1.075 = 1.155. I'm not very good at math, especially when it involves numbers. I'm not even sure the above correction is correct. The answer is supposed to be 15.5%.
I'll take a stab at your question. If you increase the case volume by 7.5%, but using the same powder charge, the velocity will go down by 7.5% but the pressure will go down by the square of the change or 7.5 x 7.5 = 15.5%. So, if the load in the smaller case was 3000 fps at 50,000 cup, in the larger case it would be 2790 fps at 43,300 cup. This is assuming you used a powder appropriate to the case volume and everything else stayed the same.
Am I even close??
NO! If your velocity drops by X feet per second, your pressure also drops, but by TWICE the percentage of velocity drop, NOT THE SQUARE!! (FYI, the square of 7.5% = 56.25%, NOT 15.5%. 15.0% is the correct answer! But you don't get 15.0 by SQUARING 7.5!!)
Quote: AC if you load one (1)of these cases a dozen times with the same load what do you get as a velocity spread? I`d hazard the ES of the load pretty much covers the vel deviation you`ve found. I don`t remember where I read it but I recall some writer stating someting on the order of a 10% increase in case volume leading to a 2.5% vel increase with equal pressures.
I support this position also. Other variables are always at work as well as case volume differences.
I said I wasn't very good at math. I knew the answer was 15 but I don't have that many fingers and it's too cold to take off my shoes so I had to resort to trying to bluff my way through and you caught me.
Quote: I don`t remember where I read it but I recall some writer stating someting on the order of a 10% increase in case volume leading to a 2.5% vel increase with equal pressures.
yup....this is in line with a lot of other data as well.
Posts: 28849 | Location: western Nebraska | Registered: 27 May 2003
I knew the answer was 15 but I don't have that many fingers and it's too cold to take off my shoes so I had to resort to trying to bluff my way through and you caught me. 
