Q: Why does data for the .300 Win Mag vary so much in different reloading manuals? Some manuals show a maximum charge of 69gn of AR2209 behind a 165gn bullet and in other manuals the maximum is listed as 70.8 in one, and 73 and 74gn in two others.
To say the least, 74gn seems to be a dangerous overload.
Andrew Hawkens
A: As you have already discovered, various handloading manuals reveal that the different bullet and powder manufacturers don’t totally agree on what constitutes a maximum handload. Some are typically more conservative than others.
For instance, one manual shows a maximum charge of 69gn, but two other manuals (Speer and Sierra) list 73 and 74gn of AR2209 to be the recommended maximum. The reason for these differences is that each company used a test barrel with different dimensions in a universal receiver while working up the loads.
Since minor variations in chamber dimensions, bore size, headspace and other factors exist from barrel to barrel and manufacturer to manufacturer, and different operators have differing techniques, this only points to the need for any handloader to start with a load well below recommended maximum and gradually work up, keeping a sharp watch for any signs of pressure.
A load that’s perfectly safe in one rifle can easily be dangerous in another.
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