Whats an M700 ? The NSS receiver wrench uses a bolt into the forward action screw hole to 100% absolutely prevent any movement of the wrench on the action. For the barrel, if it tapers, you need barrel blocks with a matching tapered hole ! The set I got for assembling my FN FAL is made like that. You put the aluminum block on the small end of the barrel and slide it rearward until the tapers match, then you line up the second one and clamp them up. Rosin is used between plates and barrel to prevent slippage.
It sounds like you don't have the right tools for the job.
Read this page Barrel Vise Use
If you call him up, I am pretty sure he can custom make you a pair of blocks for your specific barrel diameter/taper.