The M700 long action and the 721 are nearly identical. The triggers have some cosmetic differences and the bottom metal is different. Stocks will interchange with some inletting.. The standard calibers have slightly smaller diameter barrels but the magnum M700's are the same..within normal tolerances. You might consider replacing the 721 bottom metal with a M700 unit, either the standard M700 or the M700 DBM. I bought one of the latter with 2 mags for under $30 and it fit my 721 just fine. I didn't to open the barrel channel as it started as a 721 in 30-06 and I installed a custom 270 barrel.. If you're handy at all opening a barrel channel is quite simple. Yhe change in the bottom metal is more difficult unless you swap in a M700 unit..