The Unknown Munitions Magazine is desgned to only be compatible with Unknown Munitions Detachable Bottom Metal. All UM DBM lengths fit all corresponding length mags, for example the Long Action DBM fits both CIP and XL mags. NotesShort Mag (2.890" Inside Mag length) works with all aftermarket REM 700 short actionsShort XL Mag (3.150" Inside Mag length) works with BAT Machine and any other short action with a load port length 3.150" and longerMedium Mag (3.260" Inside Mag Length) works with Lone Peak, Zermatt, Stiller, and NEW Defiance XM+ spacingMedium XL Mag (3.400" Inside mag length) ONLY works with our new Medium length Vesper action at this timeMedium XLR Mag (3.250" Inside mag length) works only with all XLR Medium ChassisLong CIP Mag (3.800" Inside mag length) works with all Rem 700 Clone long actions including Defiance, Lone Peak, Zermatt, Terminus, etc.Long XL Mag (3.950" inside mag length) works with BAT Machine actions, Defiance "Seekins Cut" actions, Pierce Engineering Ac...