XM2010 Specs?

If he has a barrel chambered already and wants to be change the lug, the headspace will change.... So he can't really change the lug... 0.19 sounds like factory dimensions I've seen 0.187... You shouldn't have issues if you install the action properly... Make sure the recoil lug is in contact with the pocket for it on the reciever. Otherwise you could bend the lug with time...