I have 20g Gamecock and I would like to use some of the longer ranged loads such as heavi shot. They are not made in 2 3/4" as far as I looked.

My gun is not marked with the chamber length but I made a gage by bending a tube oblong and it slows into the taper at about 2 7/8". It will go 3" without much effort.

1. What is the nominal chamber length for a 3" 20 ga?
2. Can I shoot 3" shells in my existing chamber?
3. If not can I ream out the chamber deeper? The taper on the barrels is only .010" for 1/4".

Thanks in advance.