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Old July 31, 2020, 04:33 PM   #1
SFW
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Reloading Data Discrepancies

So I'm working on a new load for my .308 AR. I am getting wildly different data on powder loads depending on what source I use. I will be using a Hornady 165 gain SST bullet. I plan to use Hodgdon Varget for the powder. From Hornady's reloading book I get 37.6 gr to 43.2gr. for available charge weights. From the Hodgdon website I get 42.0 to 46.0C. Not really sure which one to use at this point. Any insight would be great! Thanks!
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Old July 31, 2020, 05:06 PM   #2
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You want to use Hodgon's .308 Service Rifle data which is for gas guns. This has a maximum charge of 43.2 grains with a 168-grain match bullet, but that data will work for your 165.
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Old August 1, 2020, 06:09 AM   #3
jetinteriorguy
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Whenever I get large discrepancies I usually go with the lighter load, if it accurate within that range and no pressure signs I’m good. But if there is enough case capacity to go up within a higher recommended load and that’s what it takes to get better accuracy I’ll give it a go while watching for pressure signs. It’s all about being safe and starting low and working your way up.
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Old August 1, 2020, 07:04 AM   #4
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when I see a large discrepancy I either go with the lightest as a starting load or look for a third source
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Old August 1, 2020, 07:29 AM   #5
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Also,a chronograph is invaluable. While not 100% accurate, they'll give very useful feedback as to where you are within the load range.
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Old August 1, 2020, 08:22 AM   #6
sparkyv
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This is sound advice:
Quote:
Originally Posted by jetinteriorguy View Post
Whenever I get large discrepancies I usually go with the lighter load, if it accurate within that range and no pressure signs I’m good. But if there is enough case capacity to go up within a higher recommended load and that’s what it takes to get better accuracy I’ll give it a go while watching for pressure signs. It’s all about being safe and starting low and working your way up.
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Old August 1, 2020, 08:28 AM   #7
Bart B.
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Quote:
Originally Posted by RedSoxFan View Post
Also,a chronograph is invaluable. While not 100% accurate, they'll give very useful feedback as to where you are within the load range.
Note that a 308 Winchester will shoot the same load about 250 fps faster from a 30" barrel than a 20" one; both with the same bore and groove diameters.

Almost that much difference with same length barrels but a .002" difference in groove diameters.

Arsenals loading 7.62 NATO ammo see almost a 2 grain spread in charge weights across all bulk powder lots to meet velocity and pressure specs. Commercial 308 Winchester have less spread with canistered powder lots.

How tight bullets are gripped by case necks also effects average velocity and peak pressures. 7.62 M80 ball service ammo bullet pull force spec is 60 pounds minimum but M118 match ammo is 20 pounds minimum. No idea what commercial 308 Win ammo specs are. Never seen any bullet pull force spec in reloading data. SAAMI doesn't list any in their cartridge pressure and velocity standards. I've measured pull force on reloaded 308 ammo from 1 to 73 pounds.

Last edited by Bart B.; August 1, 2020 at 09:24 AM.
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