I am confident the 20 gauge stock will work on the 28 gauge 870. I recently purchased an 870 20 gauge youth composite stock on eBay for my new .410 TSS 870 and it fit perfectly. The older "large frame" 20 gauge stocks will NOT fit. The newer "small frame" 20 gauge and the .410 have a receiver thickness of 1-1/4". I assume the same is true of the 28 gauge.