870 receiver dimensions

[Badpenny]

How many receiver sizes did remington make for the 870. I know the 12 & 20 ga are different, but what about the 28 & 410. I was told that they made a reduced size receiver for the 28.

[Virginian]

The 12 gauge is one size, and the 20, 28, and 410 are another. Because of the all steel receiver, they found they could utilize the 28 gauge size and accommodate the 20.