The Remington 870/1100/1187 assembly is one of the easiest to lighten the pull weight on by simply adding a reduced power sear spring from Patriot or Ernie. The reduced pull weight also makes the creep much less noticeable. I've had good success reducing 6-8lb triggers to a weight of 2.75-3.5lbs with those springs.
The Weatherby assembly is another that's fairly simple to modify, although not quite as wimple as the Rem.
You can make them even better with polishing, but I find that for a shotgun, 3-4lbs is plenty good for turkey hunting.
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