The 3.5" receiver guns (A400 X+, 1301 Comp, 1301 Comp Pro) have 3.5" Barrel Extensions. They are too long to fit into the 3" Receiver guns (1301 Tac, A400 Lite Synthetic). Going the other way yields improper lockup and fitment as the bolt travel is longer and the ejector is in the wrong spot, although it would fit in the receiver without the bolt carrier assy. In short, they are incompatible.
If you want a VR bbl for the 3" receiver, you need the A400 Lite Synthetic bbl (https://www.berettausa.com/en-us/bbl...tte/jb400sd28/) 28" - also available in 26" - (https://www.berettausa.com/en-us/bbl...tte/jb400sd26/) and the gas system spacer (https://www.midwestgunworks.com/page/mgwi/prod/C5F172)