I'll add my 2 cents worth on the side of --oops I had no--or little --powder in the case..............
To go a bit further--I'll add that if you load cases with powder based on faith--that is you trust your measure to drop the right amount of powder EVERY time--you will get more squibs--especially as one other poster has already mentioned--you use Lee equipment.
I use a lot of Lee products and will defend them to, well, not the death, but pretty far, but I HATE Richard Lee's idea of powder handling. I think he really truly saw no reason why any person would need to use anything but dippers...read his books...consequently all Lee powder measures I have used and I used every last one they marketed until 2009 I have found to be inadequate. Lee measures are VERY prone to bridging - at small drops and even large--though the consequences are not so disastrous when dropping large mounts of powder and only missing 2 grains out of 30 as when missing 2 grains out of 3 or 4 in handgun cartridges.
To be fair, ALL volumetric measure must be checked closely, because they are ALL prone to bridging with certain powders and especially if you have narrowed the aperture in order to drop a very small charge. My RCBS uniflow will bridge when I try to drop a lot of small charges for things like .32 acp. or .380 loads. I just get irritated about the LEE stuff because it bridges so often and so badly--and this idea that making a die that causes you to have to jerk it loose when doing a charge--does not fix the bridging problem and may even make it worse in small charge weights.
I try to only use my PACT system to weigh each and every charge--rifle or pistol, BUT sometimes you want to use up odds and ends of jugs of powder and you use a volumetric--I've learned my lesson there too-- I use my Lee dippers, so Rick has his revenge after all, a little.................
"If the enemy is in range, so are you." - Infantry Journal