Been using Norma brass in a hot rod 220 Swift for a good number of years now, and Yes it does wear out. Norma is a bit softer than most other brands on the market, and tends to allow more reloads before annealing is needed. I have as many as 10 reloads on one set before I have had to anneal, so don't think 4 is excessive.
I never use a whole 100 bag, tends to cause confusion as to the number of reloads on each set. I will split it into 25 or 50 lots, and just keep working with that lot until it wont go anymore.
Having said all this, I have found that annealing will help for a short time, but if running max or over max it wont help much unless you are very adept at the process so that the necks are tensioned the same.
As one other poster mentioned, I would lean towards a fouling issue. Throat erosion could also be part of the groups opening up as I have learned from the Swift ( and yes, throat erosion on a hot rod in under 400 rounds is definitely plausible). Unless purchased in 8lb keg, lot to lot variation of the powder can also cause your problem.
