Velocity variations with orientation

[Raptor1956]

I was checking out a reloading site and saw an interesting reference to significant variations in velocity depending on the orientation of the powder in the case. That is, if the powder in a less than full/compressed case is towards the primer the velocity can be much higher than if the powder, again in a less than full case, is closer to the bullet.

See this link ... Reloading Speeds vs. Powder Location in Case Page

If this is so and it seems reasonable then that would argue in favor of selecting a powder and charge weight combination that as nearly fills the case as possible in order to avoid these variations.

Very interesting!


Brian

[mcb]

This is true for some but not all powders. Titegroup for example can be loaded very lightly without much problem. 4.5 grains of Titegroup in a 45ACP case barely fills the case 1/3 of the way full. Another reason to use powders that fill up the case is to ensure that you cannot fit a double charge in to the case without it being noticeable. Finally there are some that claim that very light powder charges can on rare occasion detonate rather than burn blowing up guns. Cowboy action shooters seem the most likely victim of a detonation.

rambling
mcb

[fredj338]

THe variations are really only significant w/ small charges in large cases. In service rounds, I've seen very small variations over the chronograph regardless of powder location. I still like powders that fill the case 1/2 full or better. It allows for easier visual verification of the charge in the case. Except for TG, it also seems to give more uniform vel. but again, variations ins smaller cases are still small.

[Raptor1956]

So what's the limit on charge compression? If the volume of the case with the bullet at proper setback is, say, equal to 15gr of a given powder so that 15gr of powder would exactly fill the case without compression -- how many gr could you load before the powder is too compressed? Of course you don't want to overload and cause over pressure but for this question I'm more interested in just how compressable powders are...


Brian

[fredj338]

Really slow powders can be compressed quite abit, (ie, you can't put enough 2400 in a 10mm case to give yuo an over pressure load).