The groove is for 3/8" dovetail rimfire rings but there are very few modern rings that have enough "bite" to grip the shallow groove on the old 24's. The only ones I've found that are suitable are the Warne all steel rimfire rings. I have them on a .22LR/.410 and a .22 Mag/20ga and they work perfect. Have no problems shooting the shotgun barrels with scope aboard.
http://warnescopemounts.com/product/721-1-inch-7-322-medium-rings/
Last edited by SCGunNut; 10/13/17.
