Re: ?\'s on load I\'m shooting
The altitude doesn't really affect muzzle velocity, the velocity downrange is affected because of the less dense air.
What make of brass are you shooting? If you take a once fired round and weigh it, then fill it with water and weigh it, that will tell us how big it is compared to others. I use Norma brass in my 7mm and it holds 86.3gr of water, which is larger than some other brass I've used. I get less velocity and pressure signs using this brass for moderate amounts of powder than I do when using 'smaller' brass. In my experience, the smaller brass will give higher velocities with lower powder charges, but will 'top out' at a lower ultimate velocity due to the smaller ultimate volume. I notice high pressure signs at a lower powder charge with 'smaller' brass.
Hope that helps,
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