Thread: Pressure / barrel speeds?

Originally Posted by Gibo

Ok guys im trying to get my head around a few things.

Firstly pressure. Why is it lighter pills in the same cal can use more of the same powder than heavier pills. Is it to do with resistance?
How can this effect the case differently (pressure wise) ?

Secondly barrel speed?? If someone has told me my barrel is slow (tikka) how could a magnum of same cal same (tikka) go any faster?

Just getting my head around the basics of reloading so keen to learn. Hope these even make sense: D

1-The lighter pill gives less resistance to the explosive charge trying to move it, the charge is able to expand into the increased space as the lighter projectile is driven out of it's (the gas) way faster than a heavy one - the heavier projectile has more inertia for the gas to overcome before it can drive the projectile down the bore to relieve pressure by creating space (volume), so if the heavier charge is the same as the light charge, pressure spikes faster because it has nowhere to go. When the resistance is too great, the pressure will find somewhere other than the bore to go, like back through the primer and bolt vent.

2-Two barrels from the same manufacturing run, in the same length, twist rate and calibre will not (near impossible in mass production ) be identical in bore dimension, as the projectile swages to the bore, so it is gripped and rotated, the tiniest, microscopic difference in the bore dimensions will change the resistance level to the projectile, the one with greater resistance will be the slower of the two.