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9.3 Cast, Pressure, and OBT
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Old 06-06-2009, 10:06 PM
Nelsdou Nelsdou is offline
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Default 9.3 Cast, Pressure, and OBT

I experimented with a couple of loads today by utilizing QuickLoad (QL) and a number of parameters including OBT.

I had by a previous load knew my 9.3 Husky would shoot cloverleafs with the Mt Baldy cast bullets over 24 grains of AA5744, but the load printed slow and low of POA with the Husky's iron sights at 100 yds.

So I calculated the chamber pressure from QL for that load to be 21.8 ksi, a "safe" pressure for that bullet to maintain accuracy. To get a bit more speed, energy, and POI to match better to POA, I selected AA4064, a medium speed powder to try. And to expand the pressure enevolpe a bit more I took the Mt Baldy alloy at their advertised 18 BHN and multiplied it by 1280 (I believe this is a Lee guideline for pressure on lead) and got 23 ksi.

I measured my cases for actual water capacity and weighed my bullets and ran with actual numbers in QL along with AA4064 to see what velocities I could get. Once I had some ballpark velocities, I checked the OBTs for a 24 inch barrel and came up with 1.846 and 1.929 ms nodes. Then I went back and cranked QL to obtain a load that would acheive those barrel resident times and checked pressure limitations. A load of 40.1 grains would give me the 1.929 node at 21.6 ksi and 41.4 grains would give me the 1.846 node at 24 ksi, one ksi over the 23 ksi limit. I decided it was close 'nuff and loaded up both sets and went off to the range.



The first 5 shots of the 40.1 grain charge printed just where I wanted 'em but #6 through #8 fell down. The 41.4 grain charges scatter gunned so I stopped. Sure 'nuff my barrel leaded, mostly towards the muzzle end. I'm guessing something about cartridge #6 wasn't right, left lead in the barrel, and everything afterward was downhill.


The Mt Baldy bullet is the 2nd from the left and has such a big meplet that when feeding from the magazine the meplet strikes the barrel and doesn't enter the chamber. I took a Lee chamfer tool for case mouths and trimmed the meplet edge down to get these bullets to feed reliably. Easy fix, it removes very little lead from the bullet.

I think I've got a winner in that 40.1 load, just need to shore up what's giving me the leading.

Nels
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