Thread: Reloading different brand cases

as others stated biggest factor is internal volume differences = weight & brass thickness.
Lighter brass means thinner walls = more internal volume = lower pressure for same powder/projectile/seating depth load.
Weigh a few cases of cleaned brass from each brand to get a representative weight range, then do same for other brand. If the difference is more than a few grains then you'll probably need different loads, and be very careful if your load is near max pressure and you switch to heavier brass.
My experience with 284 and 270/280 brass is that the premium Euro brass like Norma and Lapua is thinner/lighter and tighter tolerances vs US brass like Win, RP, Federal or Hornady which all tend to the heavier/thicker end and greater variation.
eg in 284 my current batches of brass
Lapua = 193-194gn (another batch of Lapua 198 - 199gn)
Norma = 195 - 196gn
Win = 210 -211
Hornady = 212 - 214
Nosler (made by Norma?) = 203 -204.

In another calibre (6506ai) using RP brass vs Norma the accuracy node was ~1.3gn difference, more powder going into lighter brass and speed difference +50fps.

Different batches of brass from same brand will also vary but no where near as much as the EU vs US examples above.
I've read that there are other factors like hardness or softness of brass that differ between brands. Not sure how much practical difference this makes.