Quite often a particular powder that works for one bullet, say a FMJ, will not be compatible with a hollow point cup and core or mono metal hollow point because of the basic shape.
At times a faster or slower powder works better......
Cat
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Anytime I figure I've got this long range thing figured out, I just strap into the sling and irons and remind myself that I don't!
Is it not also because since the all copper bullets tend to be longer than the jacketed counterparts in order to make up for weight that they will generally need to be be seated deeper to allow proper cycling in most actions and magazine fit. Therefore since they need to be seated deeper the rise in pressure and the avoidance of pressure spikes, the same powders used for the jkt'd bullets should'nt be used.
Fortunately I shoot TC Pro-Hunters so case/ctg OAL isn't a concern.
In many cases, I use the same powder for cup and core bullets, as I do for all copper bullets. The only way to know what will work, is to do some testing.
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Only accurate guns are interesting.