For 13mm FBR (in Australia) ask Alt over at Oz Nerf. If your not already a member, just search Oz Nerf on google and you'll find it. I have bought 13mm foam from him before (10m worth) and the foam in loose in PETG, but perfect fit for CPVC (called Hep20 over here) For it to work effectively with my Recon, I had to mod the boltsled to push the dart further into the barrel otherwise the fit was too loose. Incase your wondering, Iím an admin/co-founder of OzNerf
It was to loose on the modded barrel or the stock one?
I measured the foam, and it's pretty much spot on 13mm ( I measured it with Digital calipers so i'm pretty sure)
I think the extra half a mm or so, just makes to to thick to be loaded in to the recon without jamming.