Main difference is the safety. When the 721 is on safe it locks the bolt closed so you have to take the safety off to cycle the action. The safety has a toggle that when moved to safe slides up into a slot cut under the bolt handles "armpit" on the bolt body. This can be cut off so the bolt can be cycled when the safety's on. The triggers are essentially the same except for this bolt lock extension on the safety lever. The 721 trigger will not work on later 700's unless this extension is cut off as there is no slot in the 700 bolt to accomidate the bolt lock lever, unless it is cut off the safety will not engage. The first few years of the 700's had this bolt lock slot and safety arrangement then it was dropped to allow for opening of the bolt with the safety on. i have a 721 with a 700 trigger on it, works fine but it will not lock the bolt when it is in the on position, and functions identically to the 700 safety. I prefer it this way as the trigger cannot be inadvertently pulled when loading unloading by cycling the bolt which you have to as 721 and 722's are blind magazines.