Some conditions that can raise pressure

Actual Case Capacity
Thick walls and/or webs will reduce internal capacity and could increase pressure.
Case Length
Cases exceeding maximum lengths could enter the chamber throat and cause pressure increases.
Case Neck Diameters
If over the maximum listed dimension, thick necks can be a source of increased pressure.
Crimping
Crimping cases can alter chamber pressure. Never crimp a load unless the load is developed with a crimp.
Component Variations
Never change component type, brand or lot number without completely redoing the necessary load development.
Excessive or Improper storage of Powders and Primers
Always use fresh primers and propellants which have been properly stored.
(See primer storage and powder storage for more info)
Excessively Deep seated or Overly Long Cartridge Lengths
Generally it is wise to load the length listed in the data tables of your reloading manual. When a specific overall length is not listed it is wise to load ammo to the maximum length specified for the loaded cartridge. When it is not possible to load short bullets to a maximum cartridge lengths, and there is no specified length, be certain to seat the bullet at least a full diameter deep. For example a 30 caliber bullet should be seated at least .308" into the case neck.
Firearms
Firearm dimensional variations can cause substantial pressure changes.
Dies
Die dimensions, which vary from normal, can cause pressure changes.

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