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Lighter is not better when it comes to shotguns,
That is your preference. If you want a 9-10 lb loaded gun (doubtful as you said you'd prefer a 3" m2 over a 3.5" m4...), sure. But a lighter gun swings quicker. And the recoil difference is negligible at these weights with the usual 1 - 1 1/4 oz target loads so that extra weight does no favours.
9 rounds vs 8 , more is better
If the $600 is worth an extra shell, then get a m4/versa max (or other 3.5") over a m3. To me, is not. It's only useful off the start, and I'm not competitive enough to drop that cash for 1 shell.
If I had the money I’d get an m2 , buy once cry once.
Which kind of negates the argument you are making (more shells, heavier is better etc...). The m2 is lighter than the m3k (with same length barrel), and is a 3" chamber.




















































