tyler2you,
If you are anywhere near Denver, We can get together some weekend when I am home and load you up a few cases of ammo for the barrel/rifle. As stated, the barrel has a shorter throat than a USGI chamber and to get the most out of it, you will need to reload.
If you haven't noticed by now, each type of bullet has a different ogive, which is the section from which a given bullet will be .224, then step down to the point/end. Since different ogives mean that the different bullet needs to be set in relationship to the throat of the chamber, and not the OAL of the round to fit the mag, some loads will need to be loaded shorter than the max mag allowed lenght. This is a good thing since if the barrel is a 1/8 twist, the 68gr bullet can be loaded to both fit the mag, and to kiss the lands (throat).
To sum it up, a shorter throated barrel is ideal for a tack driver that you plan to run ammo out of the mag, but it involves that you reload for the barrel. On the other hand, if you are going to run production ammo, you will need to pick a single round type, and then have the throat cut for it for the kiss needed (.003 off the lands). As of now, it does sound as if the throat is cut for the 77gr round, but you will need to gauge the throat to be sure of this.